Directory of Researchers
| FUJII Minoru |  |
| Graduate School of Engineering / Department of Electrical and Electronic Engineering | |
| Professor | |
| Applied Science |
Researcher Profile and Settings
Affiliation
＜Faculty / Graduate School / Others＞
Graduate School of Engineering / Department of Electrical and Electronic Engineering＜Related Faculty / Graduate School / Others＞
Faculty of Engineering / Department of Electrical and Electronic Engineering
Teaching
- Faculty of Engineering / Department of Electrical and Electronic Engineering, 2022, Electrical and Electronic Material Science
- Faculty of Engineering / Department of Electrical and Electronic Engineering, 2022, Electromagnetic Fields and Waves Ⅱ
- Graduate School of Engineering / Department of Electrical and Electronic Engineering, 2022, Advanced Solid State Physics I
- Graduate School of Engineering / Department of Electrical and Electronic Engineering, 2022, Optoelectronic Properties of Condensed Matter
Research Activities
Research Interests
Research Areas
Awards
Sep. 2012 Advanced Nano Photonics Research and Education Center in Asia, Best Poster Award, ポスター発表
発表内容が優れていたためInternational society
Jun. 2012 産業タイムズ社, 産業タイムズ社賞, ポスター発表
発表内容が優れていたためPublisher
Oct. 2011 神戸大学大学院工学研究科, 優秀教育賞, 講義
Oct. 2009 神戸大学大学院工学研究科, 優秀教育賞
Published Papers
- Last, Wiley, 24 Jan. 2023, Small, 2207318 - 2207318
[Refereed]
Scientific journal
A dielectric core-metal shell nanosphere has attracted scientific and technological interests due to the unique optical resonances arising from the hybridization of surface plasmon modes and cavity modes. The previous studies focus on a low-index dielectric core without its own optical resonances. Here, optical resonances of a core-shell nanosphere with a high refractive index (n approximate to 4) core with the lowest order Mie resonances in the visible range are investigated theoretically and experimentally. Scattering and absorption spectra of a core-shell nanosphere for different values of the core refractive index are first analyzed, and there is a transition of the hybridization scheme around n approximate to 2. Above the value, a characteristic hybridized mode with strong absorption and weak scattering emerges in the near-infrared range. A core-shell nanosphere composed of a silicon core and a gold shell is prepared, and the resonance modes are studied by single particle scattering spectroscopy and electron energy loss spectroscopy (EELS) in a transmission electron microscope. The core-shell nanospheres exhibit the hybridized modes depending on the core diameter. The hybridized mode as well as the higher order one that is not observable in the scattering spectroscopy is observed in the EELS.
Last, WILEY-V C H VERLAG GMBH, Nov. 2022, SMALL, 18 (45), English[Refereed]
Scientific journal
- 28 Oct. 2022, Journal of Applied Physics
[Refereed]
Scientific journal
- 19 Oct. 2022, ACS Photonics
[Refereed]
Scientific journal
- 06 Oct. 2022, The Journal of Physical Chemistry C
[Refereed]
Scientific journal
- 29 Sep. 2022, The Journal of Physical Chemistry C
[Refereed]
Scientific journal
Controlling ultraviolet light at the nanoscale using optical Mie resonances holds great promise for a diverse set of applications, such as lithography, sterilization, and biospectroscopy. Access to the ultraviolet requires materials with a high refractive index and wide band gap energy. Here, the authors systematically search for such materials by computing the frequency-dependent optical permittivity of 338 binary semiconductors and insulators from first principles, and evaluate their scattering properties using Mie theory. This analysis reveals several interesting candidate materials among which boron phosphide (BP) appears most promising. Then BP nanoparticles are prepared and it is demonstrated that they support Mie resonances at visible and ultraviolet wavelengths using both far-field optical measurements and near-field electron energy-loss spectroscopy. A laser reshaping method is also presented to realize spherical Mie-resonant BP nanoparticles. With a refractive index over three and low absorption losses in a broad spectral range spanning from the infrared to the near ultraviolet, BP is an appealing material for a broad range of applications in dielectric nanophotonics.
WILEY-V C H VERLAG GMBH, Aug. 2022, ADVANCED OPTICAL MATERIALS, 10 (16), English[Refereed]
Scientific journal
- 07 Jul. 2022, ECS Meeting Abstracts
[Invited]
Scientific journal
- Last, American Chemical Society ({ACS}), 18 May 2022, ACS Photonics
[Refereed]
Scientific journal
- Apr. 2022, Small
[Refereed]
Scientific journal
- American Chemical Society ({ACS}), 23 Mar. 2022, Nano Letters, 22 (6), 2320 - 2327
[Refereed]
Scientific journal
- Last, Wiley, 27 Feb. 2022, Advanced Optical Materials, 2102574 - 2102574, English
[Refereed]
Scientific journal
- 22 Feb. 2022, Advanced Optical Materials
[Refereed]
Scientific journal
- 28 Dec. 2021, Physical Review Applied
[Refereed]
Scientific journal
- Last, {IOP} Publishing, 05 Nov. 2021, Nanotechnology
[Refereed]
Scientific journal
- American Chemical Society ({ACS}), 28 Oct. 2021, The Journal of Physical Chemistry C
[Refereed]
Scientific journal
- The Optical Society, 25 Oct. 2021, Optics Express, 29 (22), 34951 - 34951
[Refereed]
Scientific journal
- Last, Wiley, 13 Oct. 2021, Small, 17 (47), 2104458 - 2104458, English
[Refereed]
Scientific journal
Walter de Gruyter {GmbH}, 01 Oct. 2021, Nanophotonics, English[Refereed]
Scientific journal
The photoelectrochemical response of a photocathode made from a colloidal solution of boron (B) and phosphorus (P) codoped silicon (Si) quantum dots (QDs) 2-11 nm in diameters is studied. Since codoped Si QDs are dispersible in alcohol and water due to the hydrophilic surface, a photoelectrode with a smooth surface is produced by drop-coating the QD solution on an indium tin oxide substrate. The codoping provides high oxidation resistance to Si QDs and makes the electrode operate as a photocathode. The photoelectrochemical response of a Si QD photoelectrode depends strongly on the size of QDs; there is a transition from anodic to cathodic photocurrent around 4 nm in diameter. Below the size, anodic photocurrent due to self-oxidation of Si QDs is observed, while above the size, cathodic photocurrent due to electron transfer across the interface is observed. The cathodic photocurrent increases with increasing the size, and in some samples, it is observed for more than 3000 s under intermittent light irradiation.
{IOP} Publishing, 08 Sep. 2021, Nanotechnology, 32 (48), English, International magazine[Refereed]
Scientific journal
- {IOP} Publishing, 10 Aug. 2021, Japanese Journal of Applied Physics
[Refereed]
Scientific journal
- Last, American Chemical Society ({ACS}), 16 Jun. 2021, ACS Photonics, 8 (6), 1794 - 1800
[Refereed]
Scientific journal
- American Chemical Society ({ACS}), 16 Jun. 2021, ACS Photonics, 8 (6), 1582 - 1591
[Refereed]
Scientific journal
- The Optical Society, 15 May 2021, OSA Continuum
[Refereed]
Scientific journal
- Last, Japan Society of Colour Material, 20 Apr. 2021, Journal of the Japan Society of Colour Material, 94 (4), 96 - 99
[Refereed]
Scientific journal
- Last, American Chemical Society ({ACS}), 24 Mar. 2021, ACS Applied Materials & Interfaces, 13 (11), 13613 - 13619
[Refereed]
Scientific journal
- Last, Wiley, 15 Feb. 2021, Advanced Photonics Research, 2 (4), 2000111 - 2000111
[Refereed]
Scientific journal
- Wiley, 15 Feb. 2021, Advanced Optical Materials, 9 (8), 2002192 - 2002192
[Refereed]
Scientific journal
- Royal Society of Chemistry ({RSC}), 2021, Nanoscale
[Refereed]
Scientific journal
- 2021, Optical Materials, 113
[Refereed]
Scientific journal
- Cambridge University Press ({CUP}), 11 Dec. 2020, MRS Communications, 10 (4), 680 - 686
[Refereed]
Scientific journal
- American Chemical Society ({ACS}), 14 Oct. 2020, Nano Letters, 20 (10), 7737 - 7743
[Refereed]
Scientific journal
It has been demonstrated recently that a nanowire (NW) of high refractive index dielectric materials works as a nanoantenna because of the excitation of the Mie-type resonances. Here, we explore the capability of a silicon (Si) NW as an optical nanoantenna by combining it with an external metallic component. We investigate the light scattering property of a single Si NW placed on a gold (Au) mirror via a very thin dielectric spacer and demonstrate strong confinement of electromagnetic fields in the gap because of the coupling of the resonance modes with a Au mirror. We demonstrate that the resonance wavelength of the hybrid mode can be tuned by the gap length, and the hybrid gap mode strongly modifies the spectral shape of the emission from a quantum dot (QD) monolayer incorporated in the gap. Quantitative analyses of the data in combination with numerical simulations reveal that the enhancement and the polarization control of the QD emission are achieved by the coupling.
Last, American Chemical Society ({ACS}), 24 Jul. 2020, ACS Applied Nano Materials, 3 (7), 7223 - 7230, English[Refereed]
Scientific journal
- {AIP} Publishing, 01 Jul. 2020, AIP Advances, 10 (7), 075302 - 075302
[Refereed]
Scientific journal
- American Chemical Society ({ACS}), 26 Jun. 2020, ACS Applied Nano Materials, 3 (6), 6099 - 6107
[Refereed]
Scientific journal
A crystalline silicon (Si) nanoparticle (NP) of 100-200 nm in diameter exhibits a highly saturated color owing to Mie resonance, and can be a component to realize angle-insensitive structural color covering the entire visible range. However, to date, coloring a substrate by Si nanostructures has only been achieved in a very small area by using electron beam lithography and dry etching processes. In this work, a Si NP color ink capable of coloring a flexible substrate by a painting process is developed. The sphericity of Si NPs is very high; the circularity factor obtained from a transmission electron microscope image reaches 0.97. The average diameter of Si nanospheres is controlled from 95 to 200 nm, and the polydispersity defined by the standard deviation divided by the average diameter is as small as 6%. Because of the high sphericity, high crystallinity, high size purity, and perfect dispersion in solution, the Si nanosphere solutions exhibit vivid colors recognizable by naked eye in a range of blue to orange. The Si nanosphere color inks combined with a polymer binder are capable of coloring flexible substrates by a painting process.
Last, Wiley, 20 Jun. 2020, Advanced Optical Materials, 8 (12), 2000033 - 2000033, English[Refereed]
Scientific journal
- Lead, The Electrochemical Society, 01 May 2020, ECS Meeting Abstracts, {MA}2020-01 (16), 1061 - 1061
[Refereed][Invited]
Scientific journal
Although the study of nonradiating anapoles has long been part of fundamental physics, the dynamic anapole at optical frequencies was only recently experimentally demonstrated in a specialized silicon nanodisk structure. We report excitation of the electrodynamic anapole state in isotropic silicon nanospheres using radially polarized beam illumination. The superposition of equal and out-of-phase amplitudes of the Cartesian electric and toroidal dipoles produces a pronounced dip in the scattering spectra with the scattering intensity almost reaching zero-a signature of anapole excitation. The total scattering intensity associated with the anapole excitation is found to be more than 10 times weaker for illumination with radially vs linearly polarized beams. Our approach provides a simple, straightforward alternative path to realizing nonradiating anapole states at the optical frequencies.
AMER PHYSICAL SOC, 06 Mar. 2020, Physical Review Letters, 124 (9), English[Refereed]
Scientific journal
- 21 Feb. 2020, Journal of Applied Physics
[Refereed]
Scientific journal
- American Chemical Society ({ACS}), 29 Jan. 2020, ACS Applied Materials & Interfaces, 12 (4), 4755 - 4768
[Refereed]
Scientific journal
Resonant excitation and manipulation of complex interactions among two or more resonances in high-index dielectric nanostructures provide great opportunities for engineering novel optical phenomena and applications. However, difficulties often arise when interpreting the observed spectra because of the overlap of the broad resonances contributed by many factors such as particle size, shape, and background index. Therefore, selective excitation of resonances that spectrally overlap with each other provides a gateway towards an improved understanding of the complex interactions. Here, we demonstrate selective excitation and enhancement of multipolar resonances of silicon nanospheres using cylindrical vector beams (CVBs) with different diameters of nanospheres and numerical apertures (NAs) of the excitations. By combining single particle spectroscopy and electrodynamic simulations, we show that the radially polarized beam can selectively excite the electric multipoles, whereas the azimuthally polarized beam can selectively excite the magnetic multipoles even though multipolar resonances are convoluted together due to their spectral overlap. Moreover, focusing the CVBs with high NA can lead to a dominant longitudinal polarization of the electric or magnetic field. We show that the enhanced longitudinal polarization with increasing NA of the radially and azimuthally polarized beams can selectively enhance the electric and magnetic multipolar resonances, respectively. Our approach can be used as a spectroscopy tool to enhance and identify multipolar resonances leading to a better understanding of light-matter interactions in other dielectric nanostructures as well as serve as a first step toward excitation of dark mode and Fano resonances in dielectric oligomers by breaking the symmetry of the nanostructures. Published under license by AIP Publishing.
Last, AMER INST PHYSICS, 21 Jan. 2020, Journal of Applied Physics, 127 (3), English[Refereed]
Scientific journal
Luminescent solar concentrator (LSC) is a promising technology to integrate semitransparent photovoltaic (PV) systems into modern buildings and vehicles. Silicon quantum dots (QDs) are good candidates as fluorophores in LSCs, due to the absence of overlap between absorption and emission spectra, high photoluminescence quantum yield (PLQY), good stability, nontoxicity, and element abundance. Herein, LSCs based on Si QDs/polymer nanocomposites are fabricated in a triplex glass configuration. A special polymer matrix (off-stoichiometric thiol-ene, OSTE) is used, which improves Si nanocrystal quantum yield. Herein, a comprehensive investigation to improve the performance of LSCs by exploring different strategies under the guidance of a theoretical description is conducted. Among these strategies, the systematical enhancement of PLQY of the nanocomposite is achieved by tuning the thiol/allyl group ratio in the OSTE matrix. In addition, ligand selection and loading optimization for QDs reduce the total scattering loss in the device. Finally, an optical power efficiency of 7.9% is achieved for an optimized LSC prototype (9 x 9 x 0.6 cm(3), transmittance approximate to 62% at 500 nm) based on Si QDs/OSTE nanocomposite, which shows good potential of this material system in LSC fabrication.
WILEY-V C H VERLAG GMBH, 2020, Solar RRL, 4 (9), English[Refereed]
Scientific journal
- Last, 2020, Advanced Optical Materials, 8 (22)
[Refereed]
Scientific journal
Gel electrophoresis, which is a standard method for separation and analysis of macromolecules such as DNA, RNA and proteins, is applied for the first time to silicon (Si) quantum dots (QDs) for size separation. In the Si QDs studied, boron (B) and phosphorus (P) are simultaneously doped. Codoping induces a negative potential on the surface of a Si QD and makes it dispersible in water. Si QDs with different B and P concentrations and grown at different temperatures (950 degrees C-1200 degrees C) are studied. It is shown that native polyacrylamide gel electrophoresis can separate codoped Si QDs by size. The capability of gel electrophoresis to immobilize size-separated QDs in a solid matrix makes detailed analyses of size-purified Si QDs possible. For example, the photoluminescence (PL) studies of the dried gel of Si QDs grown at 1100 degrees C demonstrate that a PL spectrum of a Si QD solution with the PL maximum around 1.4 eV can be separated into more than 15 spectra with the PL maximum changing from 1.2 to 1.8 eV depending on the migration distance. It is found that the relationship between the PL peak energy and the migration distance depends on the growth temperature of Si QDs as well as the B and P concentration. For all the samples with different impurity concentrations and grown at different temperatures, a clear trend is observed in the relationship between the full width at half maximum (FWHM) and the peak energy of the PL spectra in a wide energy range. The FWHM increases with the increasing peak energy and it is nearly twice larger than those observed for undoped Si QDs. The large PL FWHM of codoped Si QDs suggests that excitons are further localized in codoped Si QDs due to the existence of charged impurities.
Royal Society of Chemistry ({RSC}), 2020, Nanoscale, 12 (16), 9266 - 9271, English[Refereed]
Scientific journal
The photocatalytic hydrogen (H-2) generation by boron (B) and phosphorus (P) codoped silicon quantum dots (Si QDs) with diameters in the quantum confinement regime is investigated. The codoped Si QDs have an amorphous shell made from B, Si and P. The shell induces negative potential on the surface and makes codoped Si QDs dispersible in water. The hydrophilic shell offers enhanced stability and efficiency in photocatalytic H(2)generation and provides the opportunity to study the size dependence of the H(2)generation rate. A drastic increase of H(2)generation rate with decreasing QD size is observed. Analyses based on the Marcus theory reveal that the upper shift of the lowest unoccupied molecular orbital level of Si QDs by the quantum confinement effect is responsible for the enhanced photocatalytic activity.
Last, Royal Society of Chemistry ({RSC}), 2020, Journal of Materials Chemistry A, 8 (31), 15789 - 15794, English[Refereed]
Scientific journal
The microstructure of boron (B) and phosphorus (P) codoped silicon (Si) nanocrystals (NCs), cubic boron phosphide (BP) NCs and their mixed NCs (BxSiyPz NCs) has been studied using atom probe tomography (APT), transmission electron microscopy (TEM), and Raman scattering spectroscopy. The BxSiyPz NCs inherit superior properties of B and P codoped Si NCs such as high dispersibility in aqueous media and near infrared (NIR) luminescence and those of cubic BP NCs such as high chemical stability. The microanalyses revealed that BxSiyPz NCs are composed of a crystalline core and an amorphous shell. The core possesses a lattice constant between that of Si (diamond-cubic) and BP (cubic). The amorphous shell is comprised of B, Si and P, though the composition is not uniform and there are local B-rich, Si-rich and P-rich domains connected contiguously. The amorphous shell is proposed to be responsible for their superior chemical properties such as high dispersibility in polar solvents and high resistance to acids, and the crystalline core is responsible for the stable NIR luminescence.
Royal Society of Chemistry ({RSC}), 2020, Nanoscale, 12 (13), 7256 - 7262, English[Refereed]
Scientific journal
We demonstrate an electrically stimulated synaptic resistive switch in a silicon nanocrystal..(Si NC) thin film. A formingfree resistive switching occurs on the surface of natively oxidized Si NCs because of filaments of oxygen vacancies. To show a gradual change of the resistance, we investigate a formation mechanism of an oxygen vacancy filament. This gradual change in the resistance with input voltage pulses corresponds to short-term plasticity (STP) and long-term potentiation (LTP) in biological synapses. We simulate spike -timingdependent plasticity (STDP) in the resistive switch by voltage pulses.
Last, AMER CHEMICAL SOC, 24 Dec. 2019, ACS Applied Electronic Materials, 1 (12), 2664 - 2670, English[Refereed]
Scientific journal
Nanoimprinting followed by metal deposition is a low-cost, high-throughput, and highly reproducible process for the fabrication of large-size plasmonic substrates required for commercial products. However, the plasmonic substrates prepared by the process usually have very broad surface plasmon resonances, which cannot be well reproduced by numerical simulations. The poor agreement between experiments and calculations has prevented the detailed analysis of the field enhancement behavior and the improvement of the performance as plasmonic substrates. In this work, we demonstrate that large-area plasmonic substrates with sharp surface plasmon resonances, which can be well reproduced by numerical simulations, are produced by sputter-deposition of gold (Au) on a commercially available nanoimprinted substrate. The good agreement between experiments and simulations allow us to identify the locations and field distributions of the hot spots. The angle dependence of specular reflectance and diffuse reflectance measurements in combination with numerical simulations reveal that a dipolelike bright mode and a higher-order dark mode exist at gaps between Au nanorods. Finally, we demonstrate the application of the developed plasmonic substrates for surface-enhanced fluorescence in sandwich immunoassays for the detection of influenza virus nucleoprotein. We show that the sharp resonance and the capability of precise tuning of the resonance wavelength significantly enhance the luminescence signal. Published under license by AIP Publishing.
Last, AMER INST PHYSICS, 14 Dec. 2019, Journal of Applied Physics, 126 (22), English[Refereed]
Scientific journal
© 2019 American Chemical Society. Titanium nitride (TiN) nanostructures are promising building blocks for photothermal applications because of the surface plasmon-induced light absorption. However, compared to noble metal nanostructures, detailed analyses of the plasmonic responses of TiN nanostructures have been limited. In this work, by combining transmission electron microscopy (TEM) and single-particle spectroscopy, we determine absolute scattering cross sections of individual TiN nanocubes (NCs). The key aspect of the developed methodology is placing a TiN NC on an ultrathin SiO2 membrane and performing the precise structural analysis and the scattering spectrum measurement on the same TiN NCs. Furthermore, by employing Au nanospheres as references, we quantitatively compare the scattering spectra with those obtained for TiN NCs and determine the absolute scattering cross section as a function of NC size.
Last, American Chemical Society ({ACS}), 25 Oct. 2019, ACS Applied Nano Materials, 2 (10), 6769 - 6773[Refereed]
Scientific journal
© 2018 American Chemical Society. The effect of molecular reductants on the charge transfer-induced brightening of near-infrared photoluminescence (PL) from silicon (Si) quantum dots (QDs) was studied. Without a molecular reductant, a temporal decrease of the PL quantum yield (QY) during light irradiation in water was observed. The temporal photodarkening was reversed when a molecular reductant [sodium sulfites (Na2SO3)] was added in water. In Na2SO3-dissolved water, the PL QY increased gradually during light irradiation. The photobrightening behavior depended strongly on the amount of reductant molecules, excitation power, and the size of Si QDs. The observed phenomena suggest that an excess hole generated by trapping a photoexcited electron to a trap level is effectively removed by a reductant molecule. The observed charge transfer-induced photobrightening paves way to realize high efficiency and stable Si QDs-based phosphors usable in aqueous media.
American Chemical Society ({ACS}), 17 Jan. 2019, The Journal of Physical Chemistry C, 123 (2), 1512 - 1518, English[Refereed]
Scientific journal
- IEEE, 2019, 41st Annual International Conference of the IEEE Engineering in Medicine and Biology Society(EMBC), 3567 - 3570
International conference proceedings
Copyright © 2019 American Chemical Society. Cubic boron phosphide (BP) is an indirect band gap semiconductor with a band gap of 2.0 eV and promising for a highly stable photocatalyst to produce hydrogen from water under visible light irradiation. Here, we performed a comprehensive study on the energy-level structure and photocatalytic activity of BP nanocrystals (NCs) in the quantum confinement regime (<5 nm in diameter). First, we calculated the electronic structure of cubic BP NCs up to 2.8 nm in diameter, hexagonal BP nanoflakes, and cubic/hexagonal BP nanostructures by density functional theory and time-dependent density functional theory. We then synthesized BP NCs with 2-13 nm in diameters and performed detailed structural analyses and optical measurements. The photocatalytic bleaching experiments for dye molecules under visible light irradiation revealed that the bleaching rate depends strongly on the size of BP NCs; the increase in the band gap of BP NCs by the quantum size effects (QSE) enhanced the photocatalytic activity. The band gap increase by the QSE also enhanced the rate of photocatalytic hydrogen evolution in water.
Last, American Chemical Society ({ACS}), 2019, Journal of Physical Chemistry C, 123 (37), 23226 - 23235[Refereed]
Scientific journal
© 2019 Acta Materialia Inc. Boron (B) and phosphorous (P) co-doped colloidal silicon nanocrystals (Si NCs) have unique size-dependent optical properties, which lead to potential applications in optoelectronic and biomedical applications. However, the microstructure of the B and P co-doped colloidal Si NCs – in particular, the exact location of the dopant atoms in real space, has not been studied. A lack of understanding of this underlying question limits our ability to better control sample fabrication, as well as our ability to further develop the optical properties. To study the microstructure, a process enabling atom probe tomography (APT) of colloidal Si NCs was developed. A dispersion of colloidal Si NCs in a SiO2 sol-gel solution and a low temperature curing are demonstrated as the key sample preparation steps. Our APT results demonstrate that a B-rich region exists at the surface of the Si NCs, while P atoms are distributed within the Si NCs. First principles density functional theory calculations of a Si NC embedded in SiO2 matrix reveal that P atoms, which always prefer to reside inside a Si NC, significantly influence the distribution of B atoms. Specifically, P atoms lower the B diffusion barrier at Si/SiO2 interface and stabilize B atoms to reside within individual Si NCs. We propose that the B-modified surface changes the chemical properties of the Si NCs by (i) offering chemical resistance to attack by HF and (ii) enabling dispersibility in solution without aggregation.
2019, Acta Materialia, 178, 186 - 193, English[Refereed]
Scientific journal
© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim A designed nanoantenna exhibiting unidirectional scattering is a promising building block for novel nanophotonic devices. For device applications using nanoantennas, quantitative information on the directional scattering property is indispensable. However, experimental determination of the forward to backward scattering intensity ratio of a nano-object is not straightforward. Here, a scheme to determine the ratio quantitatively is proposed. A key technology of the scheme is placing a nano-object on a thin SiO2 membrane. Because of the low refractive index and the small thickness of the membrane, the nano-object can be treated as being suspended in free-space. This allows us to use an ideal Mie scatterer such as a spherical silicon (Si) nanocrystal as a reference to calibrate optical setups for the measurements of forward and backward scattering. Using the developed scheme, the directional scattering property of a heterodimer composed of Si and gold nanospheres synthesized by a solution process is investigated. By combining transmission electron microscopy and scattering measurements, systematic studies on the directional scattering property of a heterodimer by changing the size of a Si nanosphere is performed. It is demonstrated that strong Kerker-type forward scattering is achieved by tuning the resonance wavelength of the magnetic dipole resonance of a Si nanosphere.
Last, 2019, Advanced Optical Materials, 7 (20), English[Refereed]
Scientific journal
© 2019 Elsevier B.V. Hot electrons produced by the surface plasmon decay can be efficiently utilized to drive photochemical reactions on a semiconductor surface. Considering this aspect of plasmonics, we have evaluated the visible light photocatalytic performance of Ag–TiO2(B)–C3N4 and Au–TiO2(B)–C3N4 heterostructures in the degradation of rhodamine B (RhB) and phenol. The synergetic effect of plasmonic hot electron injection and interfacial charge transfer in the heterostructures lead to 6–9 fold enhancement in the photodecomposition rate of RhB (phenol) over TiO2(B) and C3N4. Time-resolved photoluminescence study shows fast charge transfer through the integrated network of the heterostructure. The photocurrent is measured at 470 nm, 510 nm and 575 nm, near the plasmonic excitations of Ag and Au as well as under white light illumination (400–800 nm). Plasmonic systems show more than 6-fold enhancement in photocurrent over bare TiO2(B) under illumination near monochromatic plasmonic excitation. The overall photocurrent resulting from white light illumination is 2-fold stronger than that under plasmonic excitation. The increase is due to the contribution from Ti3+ excitation, hot electron injection, and charge transfer from TiO2(B) to C3N4. We propose that Ti3+ states in TiO2(B) provide channels for direct hot electron transfer from metal to semiconductor facilitating charge separation for participation in photocatalysis.
2019, Solar Energy Materials and Solar Cells, 201, English[Refereed]
Scientific journal
A process for bioconjugation of an IgG antibody and silicon quantum dots (Si-QDs) having the luminescence in the near-infrared (NIR) range was developed. For the bioconjugation, the surface of water-soluble all-inorganic Si-QDs was functionalized by using silane-coupling agents. In amino-functionalized Si-QDs, successful conjugation was achieved without strongly affecting the luminescence property. Detailed analyses revealed that Si-QDs are bound covalently to both the light and heavy chains of an IgG antibody. It was also confirmed that the binding property of an IgG antibody with antigen nucleoprotein was not ruined by the process. The successful conjugation of an IgG antibody and NIR luminescent Si-QDs paves the way for designing environmentally friendly bio-sensing and -imaging processes.
Last, Cambridge University Press ({CUP}), 2019, MRS Communications, 9 (3), 1079 - 1086, English[Refereed]
Scientific journal
© 2019 Author(s). Active modulation of Fano resonance by light is demonstrated for an all-dielectric multilayer system containing an azo-dye-doped layer. The sample studied consists of a polystyrene layer doped with disperse red 1 (azo dye) molecules, a polyvinyl alcohol layer, and a pure polystyrene layer. In a Kretschmann attenuated-total-reflection configuration, angle-scan reflection spectra of the sample were measured with blue probe light under blue light pumping. The Fano line shape was found to change systematically depending on the intensity of the pump light. Analyses based on electromagnetic calculations of the spectra and field distributions in the layers indicate that the Fano resonance observed is generated by coupling between a broad half-leaky guided mode supported by the azo-dye-doped layer and a sharp planar waveguide mode supported by the pure polystyrene layer. The systematic changes in the Fano line shape under pump light irradiation can be well understood by a systematic decrease in light absorption in the azo-dye-doped polystyrene layer; the decrease in light absorption is due to a decrease in the extinction coefficient of the layer arising from the photoisomerization of azo dye molecules.
2019, Journal of Applied Physics, 125 (22)[Refereed]
Scientific journal
The antimicrobial activity of a hybrid nanoparticle (NP) composed of a silver (Ag) NP core decorated with silicon (Si) nanocrystals (NCs) on the exterior (Ag/Si NPs) is evaluated.
2019, RSC Advances, 9 (27), 15171 - 15176, English[Refereed]
Scientific journal
© 2019 IOP Publishing Ltd. A simple digital image analysis for measuring nanogap distance produced by adhesion lithography is proposed. Adhesion lithography produces metal electrodes with sub-15 nm undulated space and μm to mm scale width without using electron beam lithography. Although the process has been rapidly improved in recent years, there has been no generalized procedure to evaluate the nanogap distance. In this study, we propose a procedure to evaluate a nanogap electrode with large width/gap distance ratios (>1000). The procedure is to determine the average distance of nanogap space from the area and the perimeter of the space by the analysis of the grayscale image. This procedure excludes any arbitrariness of the estimation and gives quantitative comparison of nanogap electrodes produced by different processes.
Last, {IOP} Publishing, 2019, Nanotechnology, 30 (28), 285303 - 285303[Refereed]
Scientific journal
© 2019 IOP Publishing Ltd. A method that allows direct monitoring of Fano resonant behaviours of local electric fields inside a waveguide layer in multilayer structures was developed. All-dielectric multilayer structures consisting of two polystyrene waveguide layers separated by a polyvinyl alcohol spacer layer were prepared. One of the waveguide layers was doped with fluorescent dye molecules. The fluorescence spectra of the sample were measured in a Kretschmann attenuated-total-reflection geometry as a function of the angle of incidence of the excitation light. The angle-scan fluorescence excitation spectra exhibited a sharp Fano line shape superposed on a broad band. Results of electromagnetic calculations of the electric field distribution inside the multilayer structure revealed that the local electric fields inside the dye-doped waveguide layer exhibit Fano resonant behaviours due to the near-field coupling to the waveguide mode supported by another waveguide layer. Using the calculated local electric fields, theoretical fluorescence spectra were calculated based on a point dipole model. The theoretical fluorescence spectra were found to reproduce the experimental ones very well, confirming that the observed Fano line shapes in the fluorescence spectra are the manifestation of the Fano resonant behaviours of the local electric fields inside the dye-doped layer.
{IOP} Publishing, 2019, Journal of Optics (United Kingdom), 21 (10)[Refereed]
Scientific journal
Copyright © 2019 American Chemical Society. A stand-alone plasmonic nanocomposite into which a metal nanostructure and an emitting material are integrated is a promising building block for optoelectronics and biophotonics devices. Here, we present the plasmonic property of a nanocomposite composed of a Au elongated nanocap and a β-NaYF4 dielectric nanorod. We show that elongation of a Au nanocap results in splitting of the magnetic dipole resonance, and the resonance wavelengths can be controlled in a wide wavelength range by the aspect ratio. As an application of the elongated nanocap, we demonstrate strong enhancement of the near-infrared to visible upconversion of an Er3+ and Yb3+ doped β-NaYF4 nanorod by tuning the resonance wavelength of a Au nanocap placed on it to the excitation wavelength.
American Chemical Society ({ACS}), 2019, Journal of Physical Chemistry C, 123 (42), 25809 - 25815[Refereed]
Scientific journal
© 2019 Elsevier Ltd The modification of the discharge area in flat panel plasma discharge devices having a complex metal oxide protective layer on prolonged aging was demonstrated. In the case of a (Mg,Ca)O protective layer, the discharge area shrank with the discharge intensity reduced during aging. The CaO concentration was increased at the layer surface by the preferential sputtering of MgO, which is promoted by higher Xe levels in the discharge gas. These results indicate that a modified distribution of the secondary electron emission property at the surface due to the compositional change leads to the shrinkage of the discharge area. This work also demonstrated that reducing the permittivity of the dielectric layer under the protective layer expanded the discharge area, thus suppressing the degradation of the discharge intensity in the plasma discharge devices.
Elsevier {BV}, 2019, Journal of Physics and Chemistry of Solids, 130, 172 - 179[Refereed]
Scientific journal
© 2018 Elsevier Ltd The mechanism for the degradation of phosphor excitation efficiency in flat panel plasma discharge devices was investigated. We found that remaining organic compounds contained in the binders of phosphors were transformed to vacuum ultraviolet (VUV) absorbing substances over prolonged aging, which reduce the excitation efficiency of a phosphor, especially in the shorter wavelength VUV range. We also demonstrated that re-deposition of a sputtered protective layer on a phosphor further reduced the luminescence excitation efficiency due to the absorption of VUV radiation by the layer.
Elsevier {BV}, 2019, Journal of Physics and Chemistry of Solids, 124, 274 - 280[Refereed]
Scientific journal
Copyright © 2018 American Chemical Society. Micron-scale paramagnetic spheres are organized into discrete symmetric assemblies in a single step by overcoming the repulsive forces between them and balancing the magnetic attractive forces between the spheres and diamagnetic photoresist molds. Various symmetric arrangements of the spheres are obtained by modifying the shape and depth of the photoresist mold, the size of the spheres, and the magnetic susceptibilities of the paramagnetic spheres and the background medium. Permanent preservation of the assembled structure has been an issue for this type of assembly for years, because the magnetically assembled structures are maintained only under the external magnetic field. In this study, we overcome this issue by simple UV light irradiation during the magnetic assembly so that the surfaces of the sphere and substrate melt and fuse with each other, thus locking the position of the spheres on the substrate surface. This technique allowed permanent fixation of the symmetrically arranged paramagnetic spheres within 60 s, with the nanoscale spacings between adjacent spheres being maintained as narrow as 110 nm. This technique provides access to a wider variety of micro- and nanostructures and is thus useful in many research fields and industries. Particularly, such symmetric metal structures with nanogaps can serve as good media for plasmonic resonators. ©
Last, American Chemical Society ({ACS}), 26 Nov. 2018, ACS Applied Nano Materials, 1 (11), 6055 - 6062, English[Refereed]
Scientific journal
© 2018 American Chemical Society. Shallow impurity doping is an efficient route to tailor optical and electronic features of semiconductor quantum dots (QDs). However, the effect of doping is often smeared by the size, shape, and composition inhomogeneities. In this paper, we study optical properties of almost monodispersed spherical silicon (Si) QDs that are heavily doped with boron (B) and phosphorus (P). The narrow size distribution achieved by a size-separation process enables us to extract doping-induced phenomena clearly. The degree of doping-induced shrinkage of the optical band gap is obtained in a wide size range. Comparison of the optical band gap with theoretical calculations allow us to estimate the number of active donor-acceptor pairs in a QD. Furthermore, we found that the size and detection energy dependence of the luminescence decay rate is significantly modified below a critical diameter, that is ∼5.5 nm. In the diameter range above 5.5 nm, the luminescence decay rate is distributed in a wide range depending on the detection energy even in size-purified Si QDs. The distribution may arise from that of donor-acceptor distances. On the other hand, in the diameter range below 5.5 nm the detection energy dependence of the decay rate almost disappears. In this size range, which is smaller than twice of the effective Bohr radius of B and P in bulk Si crystal, the donor-acceptor distance is not a crucial factor to determine the recombination rate.
Last, American Chemical Society ({ACS}), 14 Nov. 2018, Nano Letters, 18 (11), 7282 - 7288, English[Refereed]
Scientific journal
© 2018 American Chemical Society. Annealing silicon- (Si-) rich borophosphosilicate glass (BPSG) at a high temperature results in the growth of core-shell Si quantum dots (QDs) composed of a boron (B) and phosphorus (P) codoped crystalline Si core and an amorphous shell made from B, Si, and P (B and P codoped Si QDs) in a BPSG matrix. The amorphous BxSiyPz shell is responsible for many superior properties of codoped Si QDs such as hydrophilicity, high resistance to hydrofluoric acid (HF) etching, stable luminescence in different environment, robustness of the luminescence for chemical treatments, etc. In this work, we study the growth process of the amorphous shell by Raman spectroscopy and transmission electron microscopy. We show that amorphous Si particles are first grown in a BPSG matrix within 30 s of annealing of Si-rich BPSG. After 50 s annealing, a crystalline Si core appears within an amorphous Si particle. The formation of a crystalline Si core is accompanied by the formation of an amorphous BxSiyPz shell. From the annealing time dependence of the volumes of the core and the shell, we show that supersaturated B and P are expelled to the surface of a crystalline Si core during the growth, which increases B and P concentration in an amorphous BxSiyPz shell.
American Chemical Society ({ACS}), 13 Sep. 2018, The Journal of Physical Chemistry C, 122 (36), 21069 - 21075[Refereed]
Scientific journal
- American Chemical Society ({ACS}), 16 May 2018, ACS Photonics, 5 (5), English
[Refereed]
Scientific journal
- Institute of Electrical and Electronics Engineers ({IEEE}), Mar. 2018, IEEE Sensors Letters, 2 (1), 1 - 4, English
[Refereed]
Scientific journal
- Resonant dielectric nanoparticles as efficient nanoantennas in optical regime
© 2018 OSA - The Optical Society. All rights reserved. We fabricate the colloidal Si nanoantenna exhibiting efficient Mie resonances in optical regime. The hybrid nanogap antenna structures prepared by a bottom-up approach showed the Purcell enhanced emission of QD layer integrated in the gap.
2018, Optics InfoBase Conference Papers, Part F125-JSAP 2018[Refereed]
International conference proceedings
© Springer International Publishing AG, part of Springer Nature 2018. All rights are reserved. Electrochemically etched porous silicon can exhibit pronounced optical anisotropy even though bulk silicon is basically optically isotropic. The origin of this effect, the most significant parameters, and potential applications in sensing and micro-optic devices are reviewed.
Handbook of Porous Silicon: Second Edition, 2018, Handbook of Porous Silicon: Second Edition, 1-2, 353 - 361[Refereed]
Scientific journal
- WILEY-V C H VERLAG GMBH, 2018, Physica Status Solidi (B) Basic Research, 255 (10), English
[Refereed]
Scientific journal
© The Royal Society of Chemistry. Boron (B) and phosphorus (P) codoped silicon quantum dots (Si QDs) are dispersible in polar solvents without organic ligands and exhibit photoluminescence (PL) in the first (NIR-I) and second (NIR-II) near infrared (NIR) windows in biological tissues due to the optical transition from the donor to acceptor states. We studied the relationship between the PL wavelength, lifetime and quantum yield (QY) of the colloidal solution and the composition of the starting material for the preparation. We found that the PL lifetime and the QY are primarily determined by the composition, while the PL wavelength is mainly determined by the growth temperature. By optimizing the composition, we achieved QYs of 20.1% and 1.74% in the NIR-I and NIR-II regions, respectively, in methanol. We demonstrate the application for time- gated imaging in the NIR-II range.
Royal Society of Chemistry ({RSC}), 2018, Nanoscale, 10 (29), 13902 - 13907[Refereed]
Scientific journal
© 2018 The Royal Society of Chemistry. Heavily boron and phosphorus codoped silicon quantum dots (QDs) are dispersible in water without organic ligands and exhibit near infrared luminescence. We summarize the fundamental properties and demonstrate the formation of a variety of nanocomposites.
Royal Society of Chemistry ({RSC}), 2018, Chemical Communications, 54 (35), 4375 - 4389[Refereed]
Scientific journal
- Royal Society of Chemistry ({RSC}), 2018, Nanoscale, 10 (16)
[Refereed]
Scientific journal
© 2018 American Chemical Society. We have developed an upconversion composite nanoparticle composed of a metal core, an upconversion shell, and a metal cap. Numerical simulation of the nanocomposite revealed that hybridization of the localized surface plasmon modes of the core and the cap results in the emergence of novel bonding and antibonding modes. The latter mode has wide tunability in the resonance wavelength and strong field confinement at the position of the upconversion shell. For the fabrication of the composite nanoparticle, we developed a process that combines liquid-phase synthesis and vapor deposition processes. The scattering spectra of single composite nanoparticles agreed well with those in the numerical simulation. The comparison of the upconversion intensity between the metal-core/dielectric-shell structure and the metal-core/dielectric-shell/metal-cap structure revealed that the cap formation increases the intensity several folds.
American Chemical Society ({ACS}), 2018, Journal of Physical Chemistry C, 122 (30), 17465 - 17472[Refereed]
Scientific journal
© 2018 American Chemical Society. Plasmonic nanoparticle on mirror antennas with sub-10 nm gaps have shown the great potential in nanophotonic applications because they offer tightly confined electric field in the gap and resultant large Purcell factors. However, in a nanosphere on mirror (NSoM) structure being studied experimentally, the degree of freedom of the antennas in terms of spectral and polarization control is limited. In this work, we report spectral shaping and polarization control of Purcell-enhanced fluorescence by the gap plasmon modes of an anisotropic gold (Au) nanorod on a mirror (NRoM) antenna. Systematic numerical calculations demonstrate the richer resonance behaviors of a NRoM antenna than a NSoM antenna due to the hybridization of the bright and dark modes. We fabricate a NRoM antenna by placing a Au NR on an ultraflat Au film via a mono-, double-, or quadruple-layers of light emitting quantum dots (QDs) (3 nm in diameter). The scattering spectra of single NRoM antennas coincide very well with those of the numerical simulations. We demonstrate large enhancement (>900-fold) and strong shaping of the luminescence from QDs in the gap due to the coupling with the hybridized mode of a NRoM antenna. We also show that the polarization property of the emission is controlled by that of the mode coupled.
American Chemical Society ({ACS}), 2018, ACS Photonics, 5 (8), 3421 - 3427[Refereed]
Scientific journal
© 2018 American Chemical Society. We demonstrate solution processing of hydrogen-terminated silicon nanocrystals (H-Si NCs) for flexible electronic devices. To obtain high and uniform conductivity of a solution-processed Si NC film, we adopt a perfectly dispersed colloidal H-Si NC solution. We show a high conductivity (2 × 10-5 S/cm) of a solution-processed H-Si NC film which is spin-coated in air. The NC film (area: 100 mm2) has uniform conductivity and responds to laser irradiation with 6.8 and 24.1 μs of rise and fall time. By using time-of-flight measurements, we propose a charge transport model in the H-Si NC film. For the proof-of-concept of this study, a flexible photodetector on a polyethylene terephthalate substrate is demonstrated by spin-coating colloidal H-Si NC solution in air. The photodetector can be bent in 5.9 mm bending radius at smallest, and the device properly works after being bent in 2500 cycles.
American Chemical Society ({ACS}), 2018, ACS Applied Materials and Interfaces, 10 (24), 20672 - 20678[Refereed]
Scientific journal
Copyright © 2018 American Chemical Society. Carrier multiplication (CM) is an interesting fundamental phenomenon with application potential in optoelectronics and photovoltaics, and it has been shown to be promoted by quantum confinement effects in nanostructures. However, mostly due to the short lifetimes of additional electron-hole (e-h) pairs generated by CM, major improvements of quantum dot devices that exploit CM are limited. Here we investigate CM in SiO2 solid state dispersions of phosphorus and boron codoped Si nanocrystals (NCs): an exotic variant of Si NCs whose photoluminescence (PL) emission energy, the optical bandgap, is significantly red-shifted in comparison to undoped Si NCs. By combining the results obtained by ultrafast induced absorption (IA) with PL quantum yield (PL QY) measurements, we demonstrate CM with a long (around 100 μs) lifetime of the additional e-h pairs created by the process, similar as previously reported for undoped Si NCs, but with a significantly lower CM threshold energy. This constitutes a significant step toward the practical implementation of Si-based NCs in optoelectronic devices: we demonstrate efficient CM at the energy bandgap optimal for photovoltaic conversion.
American Chemical Society ({ACS}), 2018, ACS Photonics, 5 (7), 2843 - 2849[Refereed]
Scientific journal
© 2018 The Royal Society of Chemistry. Wires and networks of Si quantum dots (QDs) with a length of over 1 μm and a width of ∼30 nm are produced by bridging Si QDs with metal ions in solution. It is shown that the width of the wires is almost independent of the preparation parameters and is always about 30 nm, except for the case when Si QDs larger than 30 nm are used, while the length of the wires depends strongly on the kinds of ions, the amount of ions and the amount of Si QDs in a solution. In addition to the microscopic size assemblies, macroscopic size rods of Si QDs with a width of ∼20 μm are produced by using Zn2+ ions. The XPS analyses reveal that Si QDs are connected to each other via a ZnO layer in the rod. The rods have much higher conductivity and photo-response than Si QD solids produced without metal ions.
Royal Society of Chemistry ({RSC}), 2018, Nanoscale, 10 (16), 7597 - 7604[Refereed]
Scientific journal
© 2018 American Chemical Society. We developed a broadband dielectric-metal hybrid nanogap resonator composed of a silicon nanoparticle (Si NP) and gold (Au) flat surface. We fabricate the nanogap resonator by depositing a monolayer of colloidal quantum dots (QDs) (∼2.8 nm in diameter) on a Au surface followed by dropping a diluted colloidal solution of Si NPs (∼150 nm in diameter). The QD monolayer acts as a precisely length-controlled nanogap as well as a light emitter to monitor the radiative properties of the nanogap resonator. We investigate the light-scattering properties of single-nanogap resonators experimentally and theoretically and found that the coupling of the Mie resonance of Si NPs with a Au surface effectively confines the electromagnetic field into the nanogap in a wider wavelength range than an all-metal nanogap resonator with a comparable size. Furthermore, we show that the resonance wavelength of the hybrid nanogap resonator is less sensitive to the gap length than that of the all-metal one. We demonstrate that the broadband hybrid nanogap resonator enhances photoluminescence of a QD monolayer integrated in the nanogap by a factor of 786.
American Chemical Society ({ACS}), 2018, ACS Photonics, 5 (5), 1986 - 1993[Refereed]
Scientific journal
© 2018 IOP Publishing Ltd. Extending our previous studies on metal-dielectric multilayer structures, we demonstrate the feasibility of generating and controlling high-Q Fano resonances in all-dielectric multilayer structures. The structures studied consist of two waveguide layers (Ge-doped SiO 2 and Al 2 O 3 layers) separated by spacer layers (SiO 2 layers) and arranged in the Kretschmann attenuated total reflection geometry. From analyses based on the electromagnetic theory, we reveal that the Fano resonance arises from the interaction between a broad waveguide mode supported by the Ge-doped SiO 2 layer and a sharp waveguide mode supported by the Al 2 O 3 layer. This mechanism allows us to generate similar Fano resonances with both the p- and s-polarized incident light. Although the Fano resonances based on radiative modes in a variety of nanostructures and metamaterials have been reported to appear only in the far-field responses, we show that the present Fano resonances appear not only in the far-field reflection spectra but also in the near-field absorption spectra.
{IOP} Publishing, 2018, Journal of Optics (United Kingdom), 20 (12)[Refereed]
Scientific journal
© Copyright 2018 American Chemical Society. We present a comprehensive ultrafast spectroscopy-based study on the delocalization of doping-induced carriers in Si nanocrystals (NCs). To this end we prepare thin films of differently sized doped Si NCs and vary the doping configurations from singly P and B doping to simultaneously P and B co-doping. We show that the NC size orchestrates the level of delocalization of the doping-induced carriers. This can be understood in light of (1) the quantum confinement effect and (2) unscreened Coulomb interactions by moving further into the nanoscale. Both contributions affect the activation energy (ΔE) that is required to create free majority carriers. By varying the NC size in combination with the doping configuration we tune ΔE and control the delocalization of the doping-induced carriers. Most importantly, we show that there is a critical NC diameter of Dcritical ≈ 6 nm that describes the transition from a localized to a free carrier regime. In particular, our results show that optical bandgaps of ∼0.95 eV (optimal for carrier multiplication-facilitated solar cell power conversion) can be achieved in P-B co-doped Si NCs with DNC < Dcritical. These results indicate that the practical photovoltaic feasibility of co-doped Si NCs is not limited by the presence of some remaining free carriers in uncompensated NCs.
American Chemical Society ({ACS}), 2018, ACS Photonics, 5 (10), 4037 - 4045[Refereed]
Scientific journal
© 2018 Author(s). We report a forming-free resistive switching using a solution-processed silicon nanocrystal (Si NC) thin film. A Si NC thin film is formed on an ITO/glass substrate by spin-coating a colloidal Si NC solution in air. The Si NC thin film shows bipolar resistive switching without a forming process. Electrical characteristics at low temperatures and in various gas environments suggest that a non-stoichiometric SiOx shell on Si NCs contributes to the resistive switching. We propose that the origin of the resistive switching is a conductive filament of oxygen vacancies on the SiOx shell by an electric field.
2018, Journal of Applied Physics, 124 (8)[Refereed]
Scientific journal
© 2018 American Chemical Society. We propose an all-painting process to produce a respiration sensor made from a humidity-sensitive nanoparticle (NP) film and a graphite trace. The sensor is fabricated under ambient air with a simple vacuum-free process for green electronics: solely hand-painting on a cellulose acetate film. A humidity-sensitive silica NP film is painted by brush on pencil-trace graphite electrodes. An all-painted humidity sensor using this film shows 106% sensitivity within a 10-93% humidity change. The film is flexible and the humidity sensor operates as a respiration sensor after bending test. We design an all-painted respiration sensor using the humidity sensor and a painted resistor. Finally, we integrate the all-painted respiration sensor, a flexible temperature sensor, and a portable data logger as a portable bifunctional health-care device. The device on a mask can monitor human respiration rate and exhaled air temperature simultaneously.
American Chemical Society ({ACS}), 2018, ACS Sustainable Chemistry and Engineering, 6 (9), 12217 - 12223[Refereed]
Scientific journal
© 2018 The Royal Society of Chemistry. We successfully visualize a core-shell structure of a heavily B and P codoped Si quantum dot (QD) by transmission electron microscopy using an ultra-thin graphene oxide support film. The enhanced contrast reveals that a codoped Si QD has a highly crystalline Si core and an amorphous shell composed of Si, B and P.
2018, Nanoscale, 10 (16), 7357 - 7362, English[Refereed]
Scientific journal
© 2018 American Chemical Society. Photocatalytic activity of water-dispersible all-inorganic Si quantum dots (QDs) with heavily B and P codoped shells was studied by monitoring bleaching of Rhodamine B (RhB) in a mixture aqueous solution of Si QDs and RhB under light irradiation. The size of Si QDs was changed from 2.8 to 9.0 nm. A strong size dependence was observed in the dissociation rate of RhB. The observed size dependence of the rate could be well explained by the Marcus theory, which considers charge transfer from the LUMO of Si QDs to that of RhB. Quenching of the photoluminescence (PL) and the shortening of the PL lifetime of Si QDs due to the electron transfer to RhB were also observed. From these two approaches, we demonstrated that the quantum size effect plays a crucial role for the enhanced photocatalytic activity of Si QDs.
American Chemical Society ({ACS}), 2018, Journal of Physical Chemistry C, 122 (3), 1874 - 1880, English[Refereed]
Scientific journal
- 2018, Chemical Communications, 54 (35), English
[Refereed]
Scientific journal
© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Silicon quantum dots (SiQDs) are interesting low-dimensional nanostructures whose unique optical and electronic properties can be exploited for imaging, biosensing, or drug delivery. SiQDs with a diameter of around 4 nm co-doped with boron and phosphorus and evincing fluorescence and dispersibility in aqueous solutions were studied with respect to their impact on different human cells. The level of SiQD cytotoxicity in different types of human cells − osteoblasts, monocytes, macrophages, and mesenchymal stromal cells – was determined. Exposing the cells to increasing concentrations of quantum dots under different conditions and the subsequent evaluation of their cytotoxicity provided an overview of cell-specific reactions to identical doses. The results revealed the importance of cultivation conditions (e.g., the formation of a protein corona on nanoparticles originating from the media supplement) as well as the significant impact of cell type (the increased sensitivity of monocytes to quantum dots in comparison to other cell types).
2018, Physica Status Solidi (B) Basic Research, 255 (10), English[Refereed]
Scientific journal
© 2018 Author(s). The enhancement of second-harmonic generation from a dielectric layer embedded in a metal-dielectric-metal structure upon excitation of surface plasmon polaritons is demonstrated experimentally. The metal-dielectric-metal structure consisting of a Gex(SiO2)1-x layer sandwiched by two Ag layers was prepared, and the surface plasmon polaritons were excited in an attenuated total reflection geometry. The measured attenuated total reflection spectra exhibited two reflection dips corresponding to the excitation of two different surface plasmon polariton modes. Strong second-harmonic signals were observed under the excitation of these surface plasmon polariton modes. The results demonstrate that the second-harmonic intensity of the Gex(SiO2)1-x layer is highly enhanced relative to that of the single layer deposited on a substrate. Under the excitation of one of the two surface plasmon polariton modes, the estimated enhancement factor falls in a range between 39.9 and 171, while under the excitation of the other surface plasmon polariton mode, it falls in a range between 3.96 and 84.6.
2018, Journal of Applied Physics, 123 (12), English[Refereed]
Scientific journal
© 2018 American Chemical Society. Phosphorus (P) and boron (B) co-doped Si nanocrystals (NCs) have raised interest in the optoelectronic industry due to their electronic tunability, optimal carrier multiplication properties, and straightforward dispersibility in polar solvents. Yet a basic understanding of the interaction of photoexcited electron-hole (e-h) pairs with new physical features that are introduced by the co-doping process (free carriers, defect states, and surface chemistry) is missing. Here, we present the first study of the ultrafast carrier dynamics in SiO2-embedded P-B co-doped Si NC ensembles using induced absorption spectroscopy through a two-step approach. First, the induced absorption data show that the large fraction of the dopants residing on the NC surface slows down carrier relaxation dynamics within the first 20 ps relative to intrinsic (undoped) Si NCs, which we interpret as enhanced surface passivation. On longer time-scales (picosecond to nanosecond regime), we observe a speeding up of the carrier relaxation dynamics and ascribe it to doping-induced trap states. This argument is deduced from the second part of the study, where we investigate multiexciton interactions. From a stochastic modeling approach we show that localized carriers, which are introduced by the P or B dopants, have minor electronic interactions with the photoexcited e-h pairs. This is understood in light of the strong localization of the introduced carriers on their original P- or B-dopant atoms, due to the strong quantum confinement regime in these relatively small NCs (<6 nm).
American Chemical Society ({ACS}), 2018, Journal of Physical Chemistry C, 122 (11), 6397 - 6404, English[Refereed]
Scientific journal
- Royal Society of Chemistry ({RSC}), 2018, Nanoscale, 10 (16), English
[Refereed]
Scientific journal
© 2017 IEEE. We demonstrate a battery-powered wearable respiration sensor chip, which monitors current due to the Grotthuss mechanism along the surface of a partially-oxidized silicon nanocrystal film. The current response is fast enough to follow humidity change due to human respiration. The response and recovery time are 72 and 44 ms, respectively. The sensor chip and a peripheral electrical circuit are mounted on a circuit board and operated by 9V battery. This respiration sensor chip is promising for a wearable respiration rate counter in health monitoring.
21 Dec. 2017, Proceedings of IEEE Sensors, 2017-December, 1 - 3, English[Refereed]
International conference proceedings
Near-field coupling between a silicon quantum dot (Si-QD) monolayer and a plasmonic substrate fabricated by nano-imprint lithography and having broad multiple resonances in the near-infrared (NIR) window of biological substances was studied by precisely controlling the QDs-substrate distance. A strong enhancement of the NIR photoluminescence (PL) of Si-QDs was observed. Detailed analyses of the PL and PL excitation spectra, the PL decay dynamics, and the reflectance spectra revealed that both the excitation cross-sections and the emission rates are enhanced by the surface plasmon resonances, thanks to the broad multiple resonances of the plasmonic substrate, and that the relative contribution of the two enhancement processes depends strongly on the excitation wavelength. Under excitation by short wavelength photons (405 nm), where enhancement of the excitation cross-section is not expected, the maximum enhancement was obtained when the QDs-substrate distance was around 30 nm. On the other hand, under long wavelength excitation (641 nm), where strong excitation cross-section enhancement is expected, the largest enhancement was obtained when the distance was minimum (around 1 nm). The achievement of efficient excitation of NIR luminescence of Si-QDs by long wavelength photons paves the way for the development of Si-QD-based fluorescence bio-sensing devices with a high bound-to-free ratio. Published by AIP Publishing.
AMER INST PHYSICS, Dec. 2017, JOURNAL OF APPLIED PHYSICS, 122 (22), 223101 - 223101, English[Refereed]
Scientific journal
© 2017 American Chemical Society. We report strong enhancements of the effective absorption cross section and photoluminescence (PL) intensity of silicon quantum dots (Si QDs) with 2.8-6.8 nm in diameter in a highly scattering dielectric medium. The scattering medium is a polymer thin film with submicrometer size pores inside, supporting the resonant cavity modes in the visible range. By the scattering associated with the cavity modes, efficient light trapping into a polymer film with ∼1 μm in thickness is achieved, which leads to 30-40 times enhancement of the effective absorption cross section of embedded Si QDs in a green-red wavelength range. The scattering medium can also enhance up to 40 times the PL of QDs. Detailed analysis reveals that the enhancements of the extraction efficiency as well as the excitation efficiency contribute to the PL enhancement.
American Chemical Society ({ACS}), 07 Jun. 2017, ACS Applied Materials & Interfaces, 9 (22), 19135 - 19142, English[Refereed]
Scientific journal
- Royal Society of Chemistry ({RSC}), 2017, Nanoscale, 9 (45)
[Refereed]
Scientific journal
© 2016 Elsevier B.V. Red luminescent bovine serum albumin conjugated gold nanospecies (BSA-Au) containing different total numbers of gold atoms and ions per one BSA molecule (AuTN/BSA) were synthesized. It is shown that pH has more influence on the emission properties than AuTN/BSA. pH sensitive and reversible emission variation (shift of the red emission peak wavelength, Δλ = 40 nm) was observed for the red emission from the BSA-Au samples. Together with the large Stokes shift in emission and the mixed singlet-triplet emission decay, it is suggested that the red emission from the BSA-Au samples agrees well with the features of metal-organic complexes.
2017, Journal of Alloys and Compounds, 691, 860 - 865[Refereed]
Scientific journal
© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim This work reports the development of an agglomeration-free colloidal solution of silicon (Si) spheres exhibiting the electric and magnetic dipole Mie resonances in the visible region as an alternative to the optical nanoantenna based on plasmonic nanoparticles. Size-controlled crystalline Si spheres with 20–250 nm in diameters are grown by a bottom-up process. The Si spheres have heavily boron (B) and phosphorus (P) codoped surface layers, which induce negative surface potential and make the spheres dispersible in alcohol almost perfectly due to the electrostatic repulsions. Formation of agglomeration-free colloidal dispersion allows to deposit Si spheres on an arbitrary substrate and to produce a dielectric nanoantenna for tailored wavelengths. This study demonstrates that, thanks to the almost perfect spherical shape of the developed Si spheres, the forward and backward scattering spectra of single Si spheres can be well-explained by the Mie resonance in a wide size range. It is demonstrated that the Si spheres work as nanoantennas for fluorescence enhancement and a single Si sphere can enhance dye fluorescence at maximum 200-fold.
2017, Advanced Optical Materials, 5 (17), 1700332 - 1700332[Refereed]
Scientific journal
© 2017 American Chemical Society. A structure composed of a monolayer of luminescent silicon quantum dots (Si-QDs) and a silver (Ag) film over nanosphere (AgFON) plasmonic nanostructure is prepared by precisely controlling the distance. A AgFON structure modifies both the photoluminescence (PL) and the PL excitation (PLE) spectra of a Si-QD monolayer significantly. It is shown that the spectral shape is very sensitive to the spacer thickness and the wavelength dependence of the PL and PLE enhancement factors agrees well with the absorptance spectra. Due to multiple surface plasmon resonances of a AgFON structure, in proper spacer thicknesses, simultaneous enhancements of the excitation cross section and the emission rate are achieved. In the wavelength range where the absorption cross section of Si-QDs is small, the PL enhancement factor averaged in a relatively wide region (10 × 10 mm2) reaches 12.
American Chemical Society ({ACS}), 2017, Journal of Physical Chemistry C, 121 (21), 11609 - 11615[Refereed]
Scientific journal
- 2017, Journal of Alloys and Compounds, 691, 860 - 865, English
[Refereed]
Scientific journal
© 2017 Elsevier B.V. In this work, the technology of the metal-insulator-semiconductor (MIS) structures with co-doped silicon nanocrystals (Si-NCs) embedded in hafnium oxide (HfOx) dielectric layer is presented. The results of structural and electrical characterization of the fabricated test structures are discussed. A good agreement between measurements of thickness of the Si-NC layers for the spectroscopic ellipsometry and AFM methods was obtained. The spectroscopic analysis demonstrated a presence of Si-NCs of optical properties similar to the monocrystalline silicon. A simulation of the capacitance-voltage-time and current-voltage-time characteristics gave results of a qualitative agreement with the measurement data. Comparative stress-and-sense measurements (I-t) for the MIS structures with and without silicon nanocrystals proved the essential difference resulting from the charging/discharging processes of the nanocrystals.
2017, Microelectronic Engineering, 178, 298 - 303, English[Refereed]
Scientific journal
© 2017 The Royal Society of Chemistry. The electrical and optical properties of semiconductor nanocrystals (NCs) can be controlled, in addition to size and shape, by doping. However, such a process is not trivial in NCs due to the high formation energy of dopants there. Nevertheless, it has been shown theoretically that in the case of B and P (acceptor/donor) codoped Si-NCs the formation energy is reduced relative to that of single type doping. Previous comprehensive measurements on ensembles of such codoped Si-NCs have pointed to the presence of donor and acceptor states within the energy gap. However, such a conjecture has not been directly verified previously. Following that, we investigate here the electronic properties of B and P codoped Si-NCs via Scanning Tunneling Spectroscopy. We monitored the quantum confinement effect in this system, for which the energy gap changed from ∼1.4 eV to ∼1.8 eV with the decrease of NC diameter from 8.5 to 3.5 nm. Importantly, all spectra showed two in-gap band-states, one close to the conduction band edge and the other to the valence band edge, which we attribute to the P and B dopant levels, respectively. The energy separation between these dopants states decrease monotonically with increasing NC diameter, in parallel to the decrease of the conduction-to-valence bands separation. A fundamental quantity that is derived directly for these Si-NCs is the intrinsic like position of the Fermi energy, a non-trivial result that is very relevant for understanding the system. Following the above results we suggest an explanation for the character and the origin of the dopants bands.
Royal Society of Chemistry ({RSC}), 2017, Nanoscale, 9 (45), 17884 - 17892, English[Refereed]
Scientific journal
© 2017 Author(s). A systematic experimental study was performed on the Fano line shape exhibited by multilayer structures consisting of an Al layer, a SiO2 spacer layer, and an Al2O3 waveguide layer. In the structures studied, a sharp Fano resonance appears on the background of broad asymmetric resonance attributed to the excitation of a surface plasmon polariton at the Al/SiO2 interface. It is shown that the background asymmetric surface plasmon resonance can be well fitted to a single Fano function, and the sharp Fano line shape can be well fitted to a double Fano function expressed as a product of two single Fano functions. The results of measurements performed by varying the spacer layer thickness indicate that the width (Q factor) of the sharp Fano resonance decreases (increases) monotonously as the thickness increases. The Q factor achieved in the present study is as high as ∼1500. A comparison with the results of electromagnetic calculations suggests that not only the spacer layer thickness but also the imaginary part of the dielectric constant of the waveguide layer plays an important role in the Fano line shape engineering.
{AIP} Publishing, 2017, Journal of Applied Physics, 122 (16), 163103 - 163103, English[Refereed]
Scientific journal
© 2017 American Chemical Society. We develop a fast-response and flexible nanocrystal-based humidity sensor for real-time monitoring of human activity: respiration and water evaporation on skin. A silicon-nanocrystal film is formed on a polyimide film by spin-coating the colloidal solution and is used as a flexible and humidity-sensitive material in a humidity sensor. The flexible nanocrystal-based humidity sensor shows a high sensitivity; current through the nanocrystal film changes by 5 orders of magnitude in the relative humidity range of 8-83%. The response/recovery time of the sensor is 40 ms. Thanks to the fast response and recovery time, the sensor can monitor human respiration and water evaporation on skin in real time. Due to the flexibility and the fast response/recovery time, the sensor is promising for application in personal health monitoring as well as environmental monitoring.
American Chemical Society ({ACS}), 2017, ACS Sensors, 2 (6), 828 - 833, English[Refereed]
Scientific journal
© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim Although, varieties of micro- to nanoscale fabrication technologies have been invented and refined for silicon (Si) processing because Si is the basic material of integrated circuits, the layouts are based on layer-by-layer approaches, making it difficult to realize three-dimensional (3D) structures with complicated shapes normal to the planar surface (along the out-of-plane direction) of the wafers used. Here, a novel and direct Si-processing technology that enables to bend thin layers of Si surfaces into various 3D curved structures at the micrometer scale is introduced. This bending is achieved by porosifying a Si wafer surface using anodic oxidation and then performing conventional photolithography patterning and wet etching. The porosity gradient in the depth direction gives rise to a stress-internalized layer in which self-rolling action is induced via subsequent patterning and wet etching. A subsequent oxidation process further enhances the curvature deformation, leading to the formation of tubes, for example. The rolling directions can be controlled by 2D patterning of the porous Si layer, which is explained well from a structural dynamics perspective. This technology has a wide range of capabilities for realizing 3D structures on Si substrates, enabling new design possibilities for Si-based on-chip devices.
2017, Small, 13 (36), English[Refereed]
Scientific journal
- 2017, Advanced Optical Materials, 5 (17), English
[Refereed]
Scientific journal
© 2017 American Chemical Society. Charge transfer interaction between colloidal silicon (Si) quantum dots (QDs) and adsorbed molecules was investigated by means of photoluminescence (PL) spectroscopy. The molecule employed is tetrathiafulvalene (TTF), which has the highest occupied molecular orbital (HOMO) near that of Si QDs and can act as an electron donor to Si QDs. The energy difference between the HOMOs of TTF and Si QDs was controlled by changing the size of Si QDs. We found that the PL of Si QDs is strongly modified by the adsorption of TTF and that the PL change is reversible, that is, removal of TTF from a colloidal solution recovers the PL intensity. In the smallest Si QDs, where the HOMO level is expected to be 0.11 eV lower than that of TTF, a 2.5-fold enhancement of the PL was observed. The PL enhancement suggests that Si QDs having p-type behavior are compensated by electron transfer from TTF, similarly to the case of substitutional phosphorus doping in Si QDs. The observed size dependence of the PL enhancement factors suggests that the charge transfer process is described by classical Marcus theory.
American Chemical Society ({ACS}), 2017, Journal of Physical Chemistry C, 121 (21), 11962 - 11967, English[Refereed]
Scientific journal
© 2017 IOP Publishing Ltd. We study the conversion efficiency of an energy harvester based on resonant tunneling through quantum dots with heat leakage. Heat leakage current from a hot electrode to a cold electrode is taken into account in the analysis of the harvester operation. Modeling of electrical output indicates that a maximum heat leakage current is not negligible because it is larger than that of the heat current harvested into electrical power. A reduction of heat leakage is required in this energy harvester in order to obtain efficient heat-to-electrical conversion. Multiple energy levels of a quantum dot can increase the output power of the harvester. Heavily doped colloidal semiconductor quantum dots are a possible candidate for a quantum-dot monolayer in the energy harvester to reduce heat leakage, scaling down device size, and increasing electrical output via multiple discrete energy levels.
2017, Nanotechnology, 28 (9), English[Refereed]
Scientific journal
© 2017 American Chemical Society. An upconversion composite nanoparticle (NP) composed of an Er and Yb doped Y2O3 (Y2O3:Yb,Er) NP and a Au nanocap was developed, and the effect of the coverage on the optical responses was studied by numerical simulations and optical measurements of single composite NPs. The formation of a composite NP and the control of the coverage were confirmed by transmission electron microscope observations. By controlling the coverage, the scattering peak due to the magnetic dipole surface plasmon resonance shifted from around 700 nm to over 900 nm. The upconversion intensity was also strongly modified by the coverage. Clear correlation was observed between the surface plasmon resonance wavelength and the upconversion intensity; the intensity increased as the resonance wavelength approached the excitation wavelength (975 nm). The largest enhancement factors of the upconversion with respect to that of a Y2O3:Yb,Er NP without a Au nanocap were 64 and 101-fold for the green (∼560 nm) and red (∼660 nm) emissions, respectively.
American Chemical Society ({ACS}), 2017, Journal of Physical Chemistry C, 121 (14), 8077 - 8083, English[Refereed]
Scientific journal
A monolayer of silicon quantum dots (Si-QDs) 2.8 and 3.9 nm in diameter is placed in a gap between a gold (Au) thin film and a Au nanoparticle, and the photoluminescence (PL) properties are studied. By the metal nanoparticle over mirror (MNPoM) structure, the PL spectra of Si-QDs are strongly modified; the full width at half maximum is reduced to similar to 170 meV, which is less than half of that of Si-QDs on a silica Substrate. The spectral shape coincides almost perfectly with that of the scattering spectrum of the MNPoM structure, indicating efficient coupling of the luminescence of Si-QDs with the gap surface plasmon modes. The luminescence intensity of Si-QDs in the gap is estimated to be enhanced about 700-fold compared to those on a Au film.
AMER CHEMICAL SOC, Dec. 2016, JOURNAL OF PHYSICAL CHEMISTRY C, 120 (50), 28795 - 28801, English[Refereed]
Scientific journal
- 神戸大学大学院工学研究科, May 2016, Memoirs of the Graduate Schools of Engineering and System Informatics Kobe University, 7, 17 - 20, English
[Refereed]
Research institution
- 2016, Mrs Communications, 6 (4), 469 - 469
[Refereed]
Scientific journal
- Silicon Nanophotonics: Basic Principles, Present Status, and Perspectives: Second Edition, 2016, Silicon Nanophotonics: Basic Principles, Present Status, and Perspectives: Second Edition, 145 - 160
[Refereed]
Scientific journal
- 2016, Physica Status Solidi (A) Applications and Materials Science, 213 (11), 2861
[Refereed]
Scientific journal
© Materials Research Society 2016. We analyze phosphorus (P)- and boron (B)-doped silicon nanocrystals (Si NCs) with various compositions of silicon-rich oxide using atom probe tomography. By creating Si iso-concentration surfaces, it is confirmed that there are two types of Si NC networks depending on the amount of excess Si. A proximity histogram shows that P prefers to locate inside the Si NCs, whereas B is more likely to reside outside the Si NCs. We discuss the difference in a preferential location between P and B by a segregation coefficient.
2016, MRS Communications, 6 (3), 283 - 288[Refereed]
Scientific journal
- Silicon Nanophotonics: Basic Principles, Present Status, and Perspectives: Second Edition, 2016, Silicon Nanophotonics: Basic Principles, Present Status, and Perspectives: Second Edition, 191 - 220
[Refereed]
Scientific journal
© the Owner Societies 2016. We report on the strongly enhanced photoluminescence (PL) and visible light photocatalysis by arrays of vertically aligned single crystalline Si nanowires (NWs) grown by Ag/Au bilayer assisted etching. High resolution FESEM and TEM imaging reveals that the Si NWs are decorated with ultra-small size arbitrary shaped Si nanocrystals (NCs) due to the lateral etching of the NWs. A strong broad band and tunable visible to near-infrared (NIR) photoluminescence (PL) in the range 1.3-2.4 eV are observed for these Si NWs/NCs at room temperature, depending on the etching conditions. Our studies reveal that the visible-NIR PL intensity is about two orders of magnitude higher and it exhibits faster decay dynamics in the bilayer assisted etching case as compared to the Ag or Au single layer etching case. The enhanced PL in the bimetal case is attributed to the longer length and higher density of the Si NWs/NCs, surface plasmon resonance enhanced absorption by residual bimetal NPs and the enhanced radiative recombination rate. Studies on the time evolution of PL spectral features with laser exposure under ambient conditions and laser power dependence reveal that both the quantum confinement of carriers in Si NCs and the nonbridging oxygen hole defects in the SiOx layer contribute to the tunable PL. Interestingly, Si NWs grown by Ag/Au bilayer assisted etching exhibit enhanced photocatalytic degradation of methylene blue in comparison to Si NWs grown by single layer Ag or Au assisted etching. The Schottky barrier present between bimetallic NPs and nanoporous Si NWs with Si-H bonds facilitates the photocatalytic activity by efficient separation of photogenerated e-h pairs. Our results demonstrate the superiority of the Si NW array grown by bilayer assisted etching for their cutting edge applications in optoelectronics and environmental cleaning.
2016, Physical Chemistry Chemical Physics, 18 (11), 7715 - 7727, English[Refereed]
Scientific journal
© 2016 American Chemical Society. Size dependence of the boron (B) acceptor and phosphorus (P) donor levels of silicon (Si) nanocrystals (NCs) measured from the vacuum level was obtained in a very wide size range from 1 to 9 nm in diameter by photoemission yield spectroscopy and photoluminescence spectroscopy for B and P codoped Si-NCs. In relatively large Si-NCs, both levels are within the bulk Si band gap. The levels exhibited much smaller size dependence compared to the valence band and conduction band edges. The Fermi level of B and P codoped Si-NCs was also studied. It was found that the Fermi level of relatively large codoped Si-NCs is close to the valence band and it approaches the middle of the band gap with decreasing the size. The results suggest that below a certain size perfectly compensated Si-NCs, that is, Si-NCs with exactly the same number of active B and P, are preferentially grown, irrespective of average B and P concentrations in samples.
2016, Nano Letters, 16 (4), 2615 - 2620, English[Refereed]
Scientific journal
© 2015 Elsevier B.V. All rights reserved. We have studied the effect of doping concentrations, growth temperature and calcinations on the structural, optical and magnetic properties of the undoped and Cr doped TiO2 nanorods/nanoribbons (NR/NRb), in order to develop an improved understanding on the mechanism of room temperature (RT) ferromagnetism (FM) in these nanostructures. Both undoped and doped TiO2 NR/NRb exhibit RT FM and a ∼2.6 fold enhancement in magnetization is observed in 0.3% Cr doped TiO2 NR/NRb as compared to the undoped NR/NRb, and the magnetization increases considerably after vacuum annealing. However, no measureable FM is observed for the precursor TiO2 powder, despite the presence of high concentration of oxygen vacancies in it. On the other hand, the magnetization decreases at higher doping concentration (0.7% Cr) as compared to 0.3% Cr doped sample. Thus, our studies revealed that a simple oxygen vacancy and/or Cr ions alone cannot yield the RT FM in TiO2 nanostructures. We argue that the oxygen vacancy with appropriate charge redistribution and their orbital overlapping, and exchange interaction with the nearby unpaired 3d electron of Ti3+ in undoped TiO2 and/or unpaired 3d electrons of Cr3+ dopant with proper charge distribution and occupation inside the host lattice in Cr doped TiO2 nanostructures play the pivotal role for the ferromagnetic ordering and observed RTFM. The presence of oxygen vacancy related F+-center and Cr3+ are confirmed from the electron spin resonance and x-ray photoelectron spectroscopy measurements.
2016, Journal of Alloys and Compounds, 661, 331 - 344, English[Refereed]
Scientific journal
© 2016 American Physical Society. Doping semiconductor nanocrystals (NCs) is a promising way to tailor the optical and electronic behavior of these materials to enable their use in (opto)electronic applications. Yet the practical exploitation of doping requires an understanding of its efficiency, and dependence on external environment, and of the electronic localization of dopant states due to confinement effects. Here, we experimentally probe the efficiency of doping of Si NCs grown in amorphous SiO2 by means of phase segregation method. We estimate a P doping efficiency of these Si NCs of about 30% and from this we infer that most P dopants are incorporated at substitutional sites of the NCs lattice and thus act as donors. We further show that the doping efficiency in Si NCs varies by several orders of magnitude depending on their external environment. Charge traps associated with air molecules adsorbed to the NCs surface give rise to a strong compensation of donors. We observe that this process can be reverted by desorbing the molecules from the NCs surface under vacuum. Moreover, we experimentally assess the confinement energy of isolated donors in Si NCs from the temperature dependence of their magnetic resonance. From this, we provide experimental evidence for the confinement-induced increase of ionization energy of dopants with decreasing NC size previously predicted with ab initio calculations of doped Si NCs.
2016, Physical Review B, 93 (11), 115425,1 - 9, English[Refereed]
Scientific journal
© 2016 The Royal Society of Chemistry. We report a novel and facile self-limiting synthesis route of silicon nanocrystal (Si NC)-based colloidally stable semiconductor-metal (gold, silver and platinum) hybrid nanoparticles (NPs). For the formation of hybrid NPs, we employ ligand-free colloidal Si NCs with heavily boron (B) and phosphorus (P) doped shells. By simply mixing B and P codoped colloidal Si NCs with metal salts, hybrid NPs consisting of metal cores and Si NC shells are spontaneously formed. We demonstrate the synthesis of highly uniform and size controllable hybrid NPs. It is shown that codoped Si NCs act as a reducing agent for metal salts and also as a protecting layer to stop metal NP growth. The process is thus self-limiting. The development of a variety of Si NC-based hybrid NPs is a promising first step for the design of biocompatible multifunctional NPs with broad material choices for biosensing, bioimaging and solar energy conversion.
2016, Nanoscale, 8 (21), 10956 - 10962, English[Refereed]
Scientific journal
© 2016 Author(s). We develop a phenomenological theory of inhomogeneous broadening in zero-dimensional systems and apply it to study photoluminescence (PL) spectra of silicon nanocrystals measured at helium and room temperatures. The proposed approach allowed us to explain experimentally observed PL peak asymmetry, linear dependence of the peak width on its maximum, and anomalous alteration of spectral characteristics with temperature increase.
2016, Applied Physics Letters, 108 (15), English[Refereed]
Scientific journal
© 2016 IOP Publishing Ltd. Si nanocrystals (Si-NCs) with extremely heavily B- and P-doped shells are developed and their structural and optical properties are studied. Unlike conventional Si-NCs without doping, B and P co-doped Si-NCs are dispersible in alcohol and water perfectly without any surface functionalization processes. The colloidal solution of co-doped Si-NCs is very stable and no precipitates are observed for more than 5 years. The co-doped colloidal Si-NCs exhibit size-controllable photoluminescence (PL) in a very wide energy range covering 0.85 to 1.85 eV. In this paper, we summarize the structural and optical properties of co-doped Si-NCs and demonstrate that they are a new type of environmentally-friendly nano-light emitter working in aqueous environments in the visible and near infrared (NIR) ranges.
2016, Nanotechnology, 27 (26), English[Refereed]
Scientific journal
© 2016 The Royal Society of Chemistry. Silicon (Si) nanostructures allow for the expansion of the application spectrum of this important semiconductor material with respect to the fields of optoelectronics and photonics. At the same time, the significant potential of Si quantum dots (SiQDs) has been revealed in terms of their potential application in the areas of biology and medicine due to their biocompatibility, low toxicity and natural biodegradability, unlike currently used semiconductor quantum dots. As far as this study is concerned, SiQDs co-doped with boron and phosphorus were used for the in vitro evaluation of their cytotoxicity in human osteoblasts. Two chemically identical types of SiQD differing in terms of their size and photoluminescence (PL) were studied. They both display long-lasting dispersion in methanol and even in aqueous media as well as PL which is not sensitive either to changes in the environment or surface modifications. Our experiments revealed significant differences between the two types of SiQD tested in regard to their behavior in a cell culture environment depending on increasing concentration (25-125 μg ml-1) and cultivation conditions (the presence or absence of proteins from the fetal bovine serum-a component of the cultivation medium). A detailed description of their optical parameters and the evaluation of zeta potential enhance the understanding of the complexities of the in vitro results obtained.
2016, RSC Advances, 6 (68), 63403 - 63413, English[Refereed]
Scientific journal
© 2016 Author(s). Colloidal silicon quantum dots (Si QDs) with a very broad photoluminescence (PL) band are proposed as a probe to monitor the Purcell enhancement in a plasmonic nanostructure. Si QDs placed on an arbitrary plasmonic nanostructure enable us to determine the Purcell enhancement factors in a broad spectral range (600-900 nm). As a proof-of-concept experiment, a layer of Si QDs is spin-coated on gold film-over nanosphere structures, and the Purcell enhancement is quantitatively determined from the analyses of the PL spectra and the decay rates. The method proposed in this work provides a facile approach to quantitatively measure the performance of plasmonic substrates for PL and Raman enhancements.
{AIP} Publishing, 2016, Applied Physics Letters, 108 (24), 241103 - 241103, English[Refereed]
Scientific journal
© 2016 The Royal Society of Chemistry. Silicon quantum dots (Si-QDs) dispersible in water and exhibiting bright near infrared (NIR) luminescence are a very attractive nano-light-emitter usable in bioimaging and biosensing. Here, we demonstrate the fabrication of NIR luminescent nanocomposites composed of Si-QDs and gold nanoparticles (Au-NPs) by DNA hybridization. We first develop processes to functionalize the surface of Si-QDs with different types of silane coupling agents without notably affecting the water solubility and the luminescence properties, and then conjugate the functionalized Si-QDs with single-stranded DNA (ssDNA). DNA hybridization with a Au-NP with complementary ssDNA results in the formation of Si-QDs/Au-NP nanocomposites.
2016, RSC Advances, 6 (68), 63933 - 63939, English[Refereed]
Scientific journal
© 2016 Author(s). We investigate a combined analysis of an energy band diagram and an equivalent circuit on nanocrystal (NC) solids. We prepared a flat silicon-NC solid in order to carry out the analysis. An energy band diagram of a NC solid is determined from DC transport properties. Current-voltage characteristics, photocurrent measurements, and conductive atomic force microscopy images indicate that a tunneling transport through a NC solid is dominant. Impedance spectroscopy gives an equivalent circuit: a series of parallel resistor-capacitors corresponding to NC/metal and NC/NC interfaces. The equivalent circuit also provides an evidence that the NC/NC interface mainly dominates the carrier transport through NC solids. Tunneling barriers inside a NC solid can be taken into account in a combined capacitance. Evaluated circuit parameters coincide with simple geometrical models of capacitances. As a result, impedance spectroscopy is also a useful technique to analyze semiconductor NC solids as well as usual DC transport. The analyses provide indispensable information to implement NC solids into actual electronic devices.
2016, Journal of Applied Physics, 119 (21), English[Refereed]
Scientific journal
© 2016 American Chemical Society. Silicon nanocrystals (Si NCs) are intensively studied for optoelectronic and biological applications due to having highly attractive features such as band engineering. Although doping is often used to control the optical and electrical properties, the related structural properties of solely doped and codoped Si NCs are not well-understood. In this study, we report the boron (B) and/or phosphorus (P) distribution in Si NCs embedded in borosilicate glass (BSG), phosphosilicate glass (PSG), and borophosphosilicate glass (BPSG) using atom probe tomography (APT). We compared solely and codoped Si NCs grown at different temperatures so that we may compare the effects of codoping and temperature on the B and/or P distribution. Proximity histograms and cluster analyses reveal that there exist boron-rich layers surrounding Si NCs and also B-P clusters within the Si NCs. Raman spectra also show a structural change between codoped Si NCs in solids and free-standing codoped Si NCs. These results lead us to understand that codoped Si NCs disperse in polar solvents.
2016, Journal of Physical Chemistry C, 120 (31), 17845 - 17852, English[Refereed]
Scientific journal
- 2016, MRS Communications, 6 (3), English
[Refereed]
Scientific journal
© Materials Research Society 2016. We demonstrate formation of allylamine (AAm) and acrylic acid (AAc)-functionalized colloidal silicon nanocrystals (Si NCs) exhibiting near-infrared (NIR) luminescence and immobilization of the NCs on substrates via covalent bond. The surface functionalization is confirmed by IR absorption spectroscopy and specific binding property of functionalized NCs. Atomic force microscope observations reveal that AAm- and AAc-functionalized Si NCs are chemically immobilized on self-assembled monolayers via covalent bonds. The functionalized Si NCs exhibit photoluminescence in a NIR region (1.5-1.6 eV), which is not significantly affected by the functionalization.
2016, MRS Communications, 6 (4), 429 - 436, English[Refereed]
Scientific journal
© 2016 Author(s). Boron (B) and phosphorous (P) codoped silicon quantum dots (Si QDs) are dispersible in polar solvents without organic ligands, and exhibit size controllable photoluminescence (PL) from 0.85 to 1.85 eV due to the electronic transitions between the donor and the acceptor states. We study the PL spectra of the codoped Si QDs at room temperature and at 77 K. We show that the broad PL band of codoped colloidal Si QDs (full width at half maximum is over 400 meV) is composed of narrower PL bands of individual QDs with different PL energies. We also show that the PL linewidth of individual codoped Si QDs is almost twice as large as those of undoped Si QDs. In contrast to the significant narrowing of the PL linewidth of undoped Si QDs at low temperatures, that of codoped Si QDs is almost independent of the temperature except for a few very small QDs. These results suggest that a large number of B and P are doped in a QD and there are a number of non-identical luminescence centers in each QD.
{AIP} Publishing, 2016, Journal of Applied Physics, 120 (16), 164307 - 164307, English[Refereed]
Scientific journal
© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim We investigated experimentally optical generation of electron–hole pairs in layers of silicon nanocrystals co-doped with phosphor and boron, dispersed in a solid-state matrix of silicon dioxide. The study was performed at room temperature. From the red-shift of the photoluminescence spectrum and the enhanced absorption at low energies appearing upon doping, the formation of additional levels inside the bandgap has been confirmed. By comparing the transient induced absorption at two excitation energies, below and well above twice the emission energy, the evidence of carrier multiplication in co-doped silicon nanocrystals has been obtained for the first time. Effect of doping on optical characteristics of silicon nanocrystals.
2016, Physica Status Solidi (A) Applications and Materials Science, 213 (11), 2863 - 2866, English[Refereed]
Scientific journal
© 2016 American Chemical Society. The optical response of an assembly of semiconductor quantum dots (QDs) is strongly modified from those of isolated ones by the inter-QD coupling. The strength of the coupling depends on the size, the inter-QD distance and the number of interacting QDs. In this work, we control these parameters of silicon (Si) QD assemblies by layer-by-layer growth of all-inorganic colloidal Si QDs. We perform detailed photoluminescence (PL) and PL decay dynamics studies for the assemblies made from monolayers of Si QDs 3.0 and 6.8 nm in diameters by precisely controlling the interlayer distance and the number of layers. From the analysis of the data with the Förster resonance energy transfer (FRET) model, we quantitatively discuss the relation between the FRET efficiency and the Förster radius in Si QD assemblies.
2016, Journal of Physical Chemistry C, 120 (42), 24469 - 24475, English[Refereed]
Scientific journal
© 2016 Author(s). We develop a facile process to integrate colloidal silicon nanocrystals (Si NCs) with metal electrodes in a single-electron transistor by self-assembly. Gold (Au) surface is modified by an amine-terminated self-assembled monolayer to have a positive potential. All-inorganic boron (B) and phosphorus (P) codoped Si NCs, with a negative surface potential and size-controllability, are selectively adsorbed on an amine-terminated Au surface by electrostatic attraction. We demonstrate the fabrication of SETs consisting of electroless-plated Au nanogap electrodes and codoped Si NCs using this process and observation of clear Coulomb diamonds at 9 K.
{AIP} Publishing, 2016, Applied Physics Letters, 109 (21), 213104 - 213104, English[Refereed]
Scientific journal
© 2015 American Chemical Society. Silicon (Si) nanocrystals (NCs) with high boron (B) and phosphorus (P) concentration shells are dispersible in polar solvents without organic ligands. In order to understand the mechanism of the solution dispersibility, the surface structure is studied by infrared absorption spectroscopy. It is shown that water molecules are adsorbed at the B-oxygen (O) bond sites on NC surface with high hydrogen bond strength, and thus B and P co-doped Si-NCs are a kind of hydrate containing large amounts of water molecules (Si-NC·xH2O). The current transport properties of Si-NC films made from the solutions are studied. It is found that the conductivity is very sensitive to the amount of adsorbed water molecules and changes by 8 orders of magnitude. The high affinity of the NC surface with water molecules is considered to be the origin of the high sensitivity.
神戸大学, 2016, Journal of Physical Chemistry C, 120 (1), 195 - 200, English[Refereed]
Scientific journal
- Sep. 2015, The Journal of Physics D, 48 (39), 395101 - 395109, EnglishSecond-order nonlinear optical behavior of amorphous SiO x thin films grown by sputtering
[Refereed]
Scientific journal
Light emitting silicon quantum dots by colloidal synthesis were uniformly spin-coated into a 20 nm-thick film and deposited atop a hyperbolic metamaterial of alternating TiN and SiO2 sub-wavelength layers. Using steady-state and time-resolved photoluminescence spectroscopy as a function of the emission wavelength in partnership with rigorous electromagnetic modeling of dipolar emission, we demonstrate enhanced Local Density of States and coupling to high-k modes in a broad spectral range. These findings provide an alternative approach for the engineering of novel Si-compatible broadband sources that leverage the control of radiative transitions in hyperbolic metamaterials and the flexibility of the widespread Si platform. (C) 2015 AIP Publishing LLC.
AMER INST PHYSICS, Jun. 2015, APPLIED PHYSICS LETTERS, 106 (24), English[Refereed]
Scientific journal
Broad visible emissions dominant at green or red have been observed for the thermally-treated Ag+ exchanged SOD zeolites, determined by the Ag+ loading contents and the excitation wavelengths. Contrary to the notable reversible green/red dominant emission evolution in the Ag+ exchanged LTA zeolites upon hydration/dehydration in air (or water vapor)/vacuum, emission spectra of the Ag+ exchanged SOD zeolites are insensitive to the environmental change. This is most probably due to the difficult H2O permeation in SOD zeolites in comparison with LTA zeolites. By combining the environment dependent emission spectra of the Ag+ exchanged LTA and SOD zeolites, we proposed the following emission mechanisms for Ag+ exchanged LTA and SOD zeolites: the green emission is due to the transition from ligand-to-metal (framework O2- -> Ag+) charge transfer state to the ground state and the red emission is due to the transition from the metal-metal (Ag+-Ag+) charge transfer state to the ground state. The insensitive environment dependent emission characteristics of Ag+ exchanged SOD zeolites may have potential applications as robust phosphors.
ROYAL SOC CHEMISTRY, 2015, Nanoscale, 7 (38), 15665 - 15671, English[Refereed]
Scientific journal
© 2015 IOP Publishing Ltd. Second harmonic generation from amorphous SiOx thin films prepared by sputtering was investigated under a nanosecond pulse excitation at 1064 nm. The investigation over a wide range of preparation conditions, i.e. excess Si concentration (C exSi) and annealing temperature, revealed that the effective second-order nonlinear optical coefficient (d eff) reaches up to 0.59 pm V-1, which is comparable to that of α-quartz. The origin was discussed based on the results of x-ray photoelectron spectroscopy, electron spin resonance spectroscopy, and photoluminescence spectroscopy. A correlation was found between the ratio of d eff to C exSi and the peak energy of the photoluminescence, suggesting that Si clusters are the most probable origin of the second-order nonlinearity.
2015, Journal of Physics D: Applied Physics, 48 (39)[Refereed]
Scientific journal
© 2015 OSA. Strong second harmonic generation (SHG) was observed from amorphous Ge doped SiO2 and Si rich SiO2 thin films. The observed maximum value of d33was 8.2 pm/V, which is 4 times larger than d22of ß-BaB2O4 crystal.
2015, Nonlinear Optics, NLO 2015[Refereed]
International conference proceedings
Energy exchange between closely packed semiconductor quantum dots allows for long-range transfer of electronic energy and enables new functionalities of nanostructured materials with a huge application potential in photonics, optoelectronics, and photovoltaics. This is illustrated by impressive advances of quantum-dot solids based on nanocrystals (NCs) of direct bandgap materials, where this effect has been firmly established. Regretfully, the (resonant) energy transfer in close-packed ensembles of NCs remains elusive for silicon the main material for electronic and photovoltaic industries. This is the subject of the present study in which we conclusively demonstrate this process taking place in dense dispersions of Si NCs in an SiO2 matrix. Using samples with different NC configurations, we can directly determine the wavelength dependent energy transfer rate and show that it (i) can be modulated by material parameters, and (ii) decreases with the NCs size, and thus being consistent with the energy flow proceeding from smaller to larger NCs. This result opens the way to new applications of Si NCs, requiring energy transport and extraction. In particular, it forms a fundamental step toward development of an excitonic all-Si solar cell, operating in some analogy to polymer devices.
AMER CHEMICAL SOC, 2015, Journal of Physical Chemistry C, 119 (33), 19565 - 19570, English[Refereed]
Scientific journal
The upconversion property of an individual composite nanoparticle consisting of a metal (Ag) nanocap and a rare-earth doped upconversion nanoparticle (Er- and Yb-doped Y2O3 nanoparticle) was studied. The structural parameters of the composite nanoparticle were chosen so that the resonant wavelengths of the electric dipole and magnetic dipole surface plasmon modes of a nanocap coincide with the upconversion luminescence peaks of Er3+. Strong modification of the upconversion spectrum was observed by the formation of a Ag nanocap. Upon excitation at 980 nm, the green (similar to 550 nm) and red (similar to 670 nm) peaks were on average 23 and 48-fold, respectively, enhanced. The strong modification of the spectral shape, i.e., the intensity ratio of the green to red luminescence, suggests that the enhancement of radiative decay rates by the two surface plasmon modes is mainly responsible for the upconversion enhancement.
AMER CHEMICAL SOC, Jan. 2015, JOURNAL OF PHYSICAL CHEMISTRY C, 119 (2), 1175 - 1179, English[Refereed]
Scientific journal
© The Royal Society of Chemistry 2015. We report a new synthetic route for cubic boron phosphide (BP) nanocrystals with diameters of 2 to 6 nm. The key concept of the synthesis process is reduction of oxides of B and P in silicon (Si)-rich borophosphosilicate glass (BPSG) into cubic BP crystals by excess Si. The size of the cubic BP crystals is controlled by the composition of the starting materials. Free-standing cubic BP nanocrystals are extracted into solution by etching out BPSG matrices. The successful growth of size controlled cubic BP nanocrystals opens the way for the development of cubic BP nanocrystal-based optoelectronic and thermoelectric devices.
2015, RSC Advances, 5 (11), 8427 - 8431, English[Refereed]
Scientific journal
© 2015 Elsevier B.V. We investigate the mechanism of red shift in photoluminescence (PL) and reduction in the PL lifetime from Si nanocrystals (NCs) decorated on vertical Si nanowires (NWs) array due to ZnO over layer coating. Arrays of vertically aligned single crystalline Si NWs decorated with arbitrary shaped Si NCs have been fabricated by a silver assisted wet chemical etching method. A strong broad band and tunable visible to near-infrared PL is observed from these Si NWs at room temperature and the Si NCs on the surface of the Si NWs are primarily responsible for the PL emission. Higher band gap ZnO film is sputter deposited on the Si NCs decorated Si NWs to form heterostructure. Bare Si NW/NCs and Si NCs/ZnO heterostructures show extremely high broad band absorption in the entire visible region. PL studies on the Si NCs/ZnO heterostructures reveal significant red shift and in some cases reduced intensity of the PL band due to the ZnO layer in close proximity of the Si NCs. This is accompanied by a reduction in the PL lifetime of the Si NCs after ZnO coating. Interestingly, no measurable red shift in PL is observed in absence of the resonance in the visible PL emission energy of ZnO and that of Si NCs. The modified PL from the heterostructures is explained through an energy band diagram on the basis of resonant energy transfer from the defect assisted recombination of the carries in the ZnO overlayer that excites the Si NCs in the close proximity and subsequent de-excitation process via radiative recombination. These findings have important bearing on the development of cost effective Si-based hybrid optoelectronic devices using wide band gap heterostructured oxide semiconductors.
2015, Journal of Alloys and Compounds, 638, 419 - 428, English[Refereed]
Scientific journal
© 2015 American Physical Society. We investigate the nanocrystallite-size and dopant-concentration dependence of the photoluminescence (PL) properties of heavily phosphorus- (P) and boron- (B) codoped Si nanocrystals (Si NCs), prepared using a combination of sputtering and ion implantation techniques. We find that the heavily doped Si NC exhibits three exotic luminescence bands, A, B, and C. The peak energy of band A redshifts with increasing dopant concentration. This band is due to the band-to-band transition at the reduced Si-NC band gap caused by the formation of impurity bands together with band-tailing effects. The PL redshift becomes large when the nanocrystallite size decreases, suggesting the occurrence of the quantum-confinement-induced carrier doping effect. The peak energies of bands B and C are independent of both the concentration and size, indicating that these bands are due to transitions between defect- and/or impurity-related localized states. Band A shows stronger thermal quenching than the PL band in pure (undoped) Si NCs, the magnitude of which depends on the dopant concentration. The stronger thermal quenching in band A is probably due to the thermally induced migration of electrons in the impurity band.
2015, Physical Review B - Condensed Matter and Materials Physics, 91 (16), 165424 - 165424, English[Refereed]
Scientific journal
© 2015 IOP Publishing Ltd. This work describes a room-temperature imprinting of nanoporous glass prepared by selective chemical etching of phase-separated glass. A highly porous (58%) and highly transparent (>90%) porous glass layer can be formed on a transparent phase-separated glass substrate. It is shown that the lateral resolution of the imprinting is a few tens of nanometers. As the porosity increases, the imprint depth increases and reaches up to 90% of the height of the mold pattern. The porous glass has a wider transmittance window (300-2700 nm) and a higher thermal durability (∼500 °C) than other materials used for imprinting. The technique has various potential applications such as diffraction optical elements, waveguides, biosensors, and microfluidic devices.
2015, Nanotechnology, 26 (25), 1 - 8, English[Refereed]
Scientific journal
© 2015 American Chemical Society. Energy transfer between silicon (Si) nanocrystals (NCs) in Si-NC solids was demonstrated by photoluminescence (PL) spectroscopy. Clear differences of PL spectra and the decay rates between solutions and solids of Si-NCs were observed. The change in the PL properties caused by the formation of solids could be explained by the energy transfer from small to large NCs in the size distribution. In order to obtain further evidence of NC-to-NC energy transfer, the size distribution was intentionally modified by mixing solutions of NCs with different size distributions. NC solids made from the mixed solutions exhibited significantly different PL spectral shape and decay rates from those made from unmixed solutions, providing clear evidence of NC-to-NC energy transfer in Si-NC solids.
2015, Journal of Physical Chemistry Letters, 6 (14), 2761 - 2766, English[Refereed]
Scientific journal
© 2015 American Chemical Society. Energy exchange between closely packed semiconductor quantum dots allows for long-range transfer of electronic energy and enables new functionalities of nanostructured materials with a huge application potential in photonics, optoelectronics, and photovoltaics. This is illustrated by impressive advances of quantum-dot solids based on nanocrystals (NCs) of direct bandgap materials, where this effect has been firmly established. Regretfully, the (resonant) energy transfer in close-packed ensembles of NCs remains elusive for silicon-the main material for electronic and photovoltaic industries. This is the subject of the present study in which we conclusively demonstrate this process taking place in dense dispersions of Si NCs in an SiO
2015, Journal of Physical Chemistry C, 119 (33), 19565 - 19570, English2 matrix. Using samples with different NC configurations, we can directly determine the wavelength dependent energy transfer rate and show that it (i) can be modulated by material parameters, and (ii) decreases with the NCs size, and thus being consistent with the energy flow proceeding from smaller to larger NCs. This result opens the way to new applications of Si NCs, requiring energy transport and extraction. In particular, it forms a fundamental step toward development of an excitonic all-Si solar cell, operating in some analogy to polymer devices.[Refereed]
Scientific journal
© 2015 AIP Publishing LLC. We report the development of bio-compatible cellulose nanofibers doped with light emitting silicon nanocrystals and Au nanoparticles via facile electrospinning. By performing photoluminescence (PL) spectroscopy as a function of excitation wavelength, we demonstrate plasmon-enhanced PL by a factor of 2.2 with negligible non-radiative quenching due to plasmon-enhanced scattering of excitation light from Au nanoparticles to silicon nanocrystals inside the nanofibers. These findings provide an alternative approach for the development of plasmon-enhanced active systems integrated within the compact nanofiber geometry. Furthermore, bio-compatible light-emitting nanofibers prepared by a cost-effective solution-based processing are very promising platforms for biophotonic applications such as fluorescence sensing and imaging.
2015, Applied Physics Letters, 107 (4), 041111 - 041111, English[Refereed]
Scientific journal
© 2015 American Chemical Society. We develop colloidal nanocomposites consisting of coupled light-emitting Si nanocrystals (NCs) and Au nanorods and systematically investigate their structural and photoluminescence (PL) properties, which demonstrate significant enhancement of spontaneous emission rate with suppressed nonradiative quenching. In addition, through a comparison of the polarization dependence of PL and scattering intensities of single nanocomposites, we successfully demonstrate that the emission from Si NCs coupled to Au nanorods is highly polarized along the major axis of nanorods. The experimental results in combination with rigorous simulations of dipolar emission in the vicinity of Au nanorods enable us to demonstrate a ∼3 times enhancement of the quantum efficiency at the peak of the NC emission. The Si-based active plasmonic-coupled nanocomposites developed in this work provide novel opportunities for biocompatible platforms that leverage nanoscale fluorescent probes for biosensing and bioimaging device applications.
2015, ACS Photonics, 2 (9), 1298 - 1305, English[Refereed]
Scientific journal
© The Royal Society of Chemistry 2015. Broad visible emissions dominant at green or red have been observed for the thermally-treated Ag+ exchanged SOD zeolites, determined by the Ag+ loading contents and the excitation wavelengths. Contrary to the notable reversible green/red dominant emission evolution in the Ag+ exchanged LTA zeolites upon hydration/dehydration in air (or water vapor)/vacuum, emission spectra of the Ag+ exchanged SOD zeolites are insensitive to the environmental change. This is most probably due to the difficult H2O permeation in SOD zeolites in comparison with LTA zeolites. By combining the environment dependent emission spectra of the Ag+ exchanged LTA and SOD zeolites, we proposed the following emission mechanisms for Ag+ exchanged LTA and SOD zeolites: the green emission is due to the transition from ligand-to-metal (framework O2- → Ag+) charge transfer state to the ground state and the red emission is due to the transition from the metal-metal (Ag+-Ag+) charge transfer state to the ground state. The insensitive environment dependent emission characteristics of Ag+ exchanged SOD zeolites may have potential applications as robust phosphors.
2015, Nanoscale, 7 (38), 15665 - 15671, English[Refereed]
Scientific journal
© 2015 American Chemical Society. A composite nanoparticle (NP) consisting of a gold nanoparticle (Au-NP) core and a thick shell of silicon quantum dot (Si-QD) agglomerates was developed. In the composite NPs with an optimized amount of Si-QDs per a Au-NP, photoluminescence from Si-QDs was enhanced, when it was excited in the wavelength range of the localized surface plasmon resonances (LSPRs) of Au-NPs. The experimental results could be well-explained by a simple model consisting of a spherical Au-NP and a spherical shell made from Si-QD aggregates. It was found that the enhancement is due to increased excitation efficiency of Si-QDs via the LSPR of Au-NPs.
2015, Journal of Physical Chemistry C, 119 (44), 25108 - 25113, English[Refereed]
Scientific journal
© 2015, Nature Publishing Group. All rights reserved. Si nanocrystals (NCs) are often prepared by thermal annealing of multiple stacks of alternating sub-stoichiometric SiOx and SiO2 nanolayers. It is frequently claimed that in these structures, the NC diameter can be predefined by the thickness of the SiOx layer, while the NC concentration is independently controlled by the stoichiometry parameter x. However, several detailed structural investigations report that the NC size confinement to within the thickness of the SiOxlayer is not strictly obeyed. In this study we address these contradicting findings: based on cross-correlation between structural and optical characterization of NCs grown in a series of purposefully prepared samples of different stoichiometry and layer thickness, we develop a comprehensive understanding of NC formation by Si precipitation in multinanolayer structures. We argue that the narrow NC size distribution generally observed in these materials appears due to reduction of the Si diffusion range, imposed by the SiO2 spacer layer. Therefore, both the SiOx layer thickness and composition as well as the actual thickness of the SiO2 spacer play an essential role in the NC formation.
2015, Scientific Reports, 5 (17289), 1 - 6, English[Refereed]
Scientific journal
© 2015 The Royal Society of Chemistry. We develop a new type of boron (B)-rich nanocrystals (NCs) for applications in Boron Neutron Capture Therapy (BNCT). Phase separation of oxygen (O) deficient borophosphosilicate glasses (BPSG) by annealing in inert ambient gas results in the growth of different types of B-rich NCs. When the silicon (Si) concentration is much higher than the others, B and phosphorus (P) co-doped Si-NCs are grown. In the opposite case, cubic boron phosphide (BP) NCs are grown. In between two extremes, we demonstrate the growth of a new type of cubic NCs consisting of B, Si and P with an average B concentration up to 36 at%. The B-rich NCs are dispersible in water and exhibit photoluminescence in the biological window. These properties in combination with the capability of the bio-functionalization via the surface Si-hydrogen (H) and Si-O bonds suggest that the B-rich NCs can be a multifunctional biomaterial used for imaging, diagnosis and BNCT.
2015, RSC Advances, 5 (119), 98248 - 98253, English[Refereed]
Scientific journal
The usefulness of polarized second harmonic generation (SHG) microscopy to determine crystallographic orientations of domains in polycrystalline films was demonstrated. Orientation of alpha-quartz like GeO2 (alpha-GeO2) domains in polycrystalline films were investigated by using polarized SHG and Raman microscopy. It was found that the SHG intensity of a alpha-GeO2 polycrystalline film depends strongly on measurement points and excitation and detection polarizations, while the Raman intensity was almost uniform in the whole mapping area. Analyses of the SHG mappings in different polarization conditions allowed us to determine not only the size and shape of crystalline domains, but also the crystallographic orientations.
IOP PUBLISHING LTD, Nov. 2014, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 47 (45), 1 - 7, English[Refereed]
Scientific journal
Er3+/YD3+ doped MnF2 nanostructures have been prepared via a solvothermal method. The morphology of the nanocrystals could be well controlled from nanoparticles to nanoclusters and nanolanterns by varying the volume ratio between oleic acid and ethanol in the solvent. Moreover, the size is tuned from 200 nm to 1.5 gm with the increase of reaction temperature from 110 to 200 degrees C. It is shown that controlling the doping concentration (Yb3+ <= 20 mol%) is essential to preserve the single phase and morphology of the MnF2 host. Single-band red upconversion (UC) emission can be generated in Er3+ single and Er3+/Yb3+ codoped MnF2 nanoclusters due to the energy transfer between host Mn2+ and dopant Er3+ ions. The detailed studies suggest that our MnF2:Er3+/Yb3+ nanocrystals have the strongest single-band luminescence feature at the dopant concentrations of Er3+ (2 mol%) and Yb3+ (20 mol%). The brighter red emission from the current nanostructure compared with those from NaYF4:Er3+/Yb3+ has shown its suitability as an efficient UC luminescence host. It is expected that the achieved intense pure red emission may have potential application in in vivo bioimaging.
ROYAL SOC CHEMISTRY, Mar. 2014, JOURNAL OF MATERIALS CHEMISTRY C, 2 (9), 1736 - 1741, English[Refereed]
Scientific journal
Si1-xGex alloy nanocrystals potentially have superior properties compared to Si nanocrystals such as an enhanced absorption cross-section and wider controllability of the band gap energy. However, reports on the synthesis of Si1-xGex alloy nanocrystals, especially colloidal Si1-xGex alloy nanocrystals, are still very limited and the quality is not as high as that of colloidal Si nanocrystals. Here, we report the development of a new type of luminescent colloidal Si1-xGex alloy nanocrystals of 3 to 6 nm in diameter. The characteristic feature of the Si1-xGex alloy nanocrystals is the formation of a high B and P concentration layer on the surface. The shell provides inorganic atomic ligands and B and P co-doped Si1-xGex nanocrystals can be dispersed in alcohol without any surface functionalization processes.
ROYAL SOC CHEMISTRY, 2014, JOURNAL OF MATERIALS CHEMISTRY C, 2 (28), 5644 - 5650, English[Refereed]
Scientific journal
- 2014, Nanoscale, 6 (21), 12354 - 12359
[Refereed]
Scientific journal
© Springer International Publishing Switzerland 2014. All rights are reserved. Electrochemically etched porous silicon can exhibit pronounced optical anisotropy even though bulk silicon is basically optically isotropic. The origin of this effect, the most significant parameters, and potential applications in sensing and micro-optic devices are reviewed.
Handbook of Porous Silicon, 2014, Handbook of Porous Silicon, 245 - 253[Refereed]
Scientific journal
© 2014 IOP Publishing Ltd. The usefulness of polarized second harmonic generation (SHG) microscopy to determine crystallographic orientations of domains in polycrystalline films was demonstrated. Orientation of α-quartz like GeO2 (α-GeO2) domains in polycrystalline films were investigated by using polarized SHG and Raman microscopy. It was found that the SHG intensity of a α-GeO2 polycrystalline film depends strongly on measurement points and excitation and detection polarizations, while the Raman intensity was almost uniform in the whole mapping area. Analyses of the SHG mappings in different polarization conditions allowed us to determine not only the size and shape of crystalline domains, but also the crystallographic orientations.
2014, Journal of Physics D: Applied Physics, 47 (45)[Refereed]
Scientific journal
The optical properties of zeolites annealed at various temperatures are investigated for the first time. The annealed zeolites exhibit strong white photoluminescence (PL) under ultraviolet light excitation. With increasing annealing temperature, the emission intensity of annealed zeolites first increases and then decreases. At the same time, the PL peak red-shifts from 495 nm to 530 nm, and then returns to 500 nm. The strongest emission appears when the annealing temperature is 500 C. The quantum yield of the sample is measured to be ~10%. The PL lifetime monotonously increases from 223 μs to 251 μs with increasing annealing temperature. The origin of white PL is ascribed to oxygen vacancies formed during the annealing process. © 2013 Elsevier B.V.
2014, Journal of Luminescence, 145, 288 - 291, English[Refereed]
Scientific journal
Er3+/Yb3+ doped MnF2 nanostructures have been prepared via a solvothermal method. The morphology of the nanocrystals could be well controlled from nanoparticles to nanoclusters and nanolanterns by varying the volume ratio between oleic acid and ethanol in the solvent. Moreover, the size is tuned from 200 nm to 1.5 μm with the increase of reaction temperature from 110 to 200 °C. It is shown that controlling the doping concentration (Yb3+ ≤ 20 mol%) is essential to preserve the single phase and morphology of the MnF2 host. Single-band red upconversion (UC) emission can be generated in Er3+ single and Er3+/Yb3+ codoped MnF2 nanoclusters due to the energy transfer between host Mn2+ and dopant Er3+ ions. The detailed studies suggest that our MnF2:Er3+/Yb 3+ nanocrystals have the strongest single-band luminescence feature at the dopant concentrations of Er3+ (2 mol%) and Yb3+ (20 mol%). The brighter red emission from the current nanostructure compared with those from NaYF4:Er3+/Yb3+ has shown its suitability as an efficient UC luminescence host. It is expected that the achieved intense pure red emission may have potential application in in vivo bioimaging. © 2014 The Royal Society of Chemistry.
2014, Journal of Materials Chemistry C, 2 (9), 1736 - 1741, English[Refereed]
Scientific journal
© The Royal Society of Chemistry 2014. We have developed a facile low-temperature synthetic method for the preparation of NaMnF3 nanocubes with Er3+ and Yb3+ ions homogeneously incorporated in the host lattice. The effects of the reaction temperature, and the volume ratio between ethanol and DI water on the morphology of NaMnF3 nanocubes are systematically investigated. The NaMnF3 nanocubes can be produced in the low temperature range (25-80°C), and the higher reaction temperature (80°C) is favorable for the formation of a smooth surface. The formation of NaMnF3 nanocubes strongly depends on the ethanol solvent. The morphology and single-phase of the obtained samples could be well maintained by controlling the doping concentration (Yb3+ ≤ 20 mol%). Single-band red upconversion emission can be generated in Er3+/Yb3+ codoped NaMnF3 nanocubes due to the energy transfer between host Mn2+ and dopant Er3+ ions. It is revealed that our NaMnF3:Er3+/Yb3+ nanocubes irradiate the brightest red luminescence at the dopant concentrations of Er3+ (2 mol%) and Yb3+ (15 mol%), which is stronger than that of the hexagonal-phase NaYF4:Er3+/Yb3+ phosphor.
2014, RSC Advances, 4 (106), 61891 - 61897, English[Refereed]
Scientific journal
© 2014 the Partner Organisations. We present a new route for mass-production of B and P codoped all-inorganic colloidal Si nanocrystals (NCs) from hydrogen silsesquioxane (HSQ). Codoped Si NCs are grown in glass matrices by annealing mixture solutions of HSQ and dopant acids, and then extracted from the matrices by hydrofluoric acid etching. The free-standing NCs are dispersible in methanol without any surface functionalization processes. The structural analyses suggest the formation of heavily B and P doped hydrophilic shells on the surface of Si NCs. The NCs show efficient size-tunable photoluminescence in the near infrared to visible region.
2014, Nanoscale, 6 (21), 12354 - 12359, English[Refereed]
Scientific journal
We report on the lattice strain dependence of the nonlinear optical (NLO) parameters of strained Si nanoparticles (NPs), which are prepared in a controlled way by a mechanical ball milling process. X-ray diffraction analysis shows that the nature of strain is compressive and is primarily caused by milling-induced lattice dislocations, which is further supported by high-resolution transmission electron microscopy imaging. It is found that the nonlinear refractive index (n2) and nonlinear absorption coefficient (β) are strongly influenced by the associated lattice strain present in Si NPs. With the increase of lattice strain, the β gradually decreases while n2 increases slowly. The strain-dependent observed changes in the NLO parameters of Si NPs are found to be advantageous for application purpose, and it is explained on the basis of strain-induced modification in the electronic structure of the highest occupied molecular orbital and lowest unoccupied molecular orbital states of Si NPs. These results demonstrate the potential of straindependent enhancement of nonlinearities for silicon photonics applications. © 2014 Optical Society of America.
2014, Optics Letters, 39 (13), 3833 - 3836, English[Refereed]
Scientific journal
Boron (B) and phosphorus (P) codoped silicon (Si) nanocrystals, which exhibit very wide range tunable luminescence due to the donor to acceptor transitions and can be dispersed in polar liquids without organic ligands, are studied by Raman scattering and X-ray photoelectron spectroscopies. Codoped Si nanocrystals exhibit a Raman spectrum significantly different from those of intrinsic ones. First, the Raman peak energy is almost insensitive to the size and is very close to that of bulk Si crystal in the diameter range of 2.7 to 14 nm. Second, the peak is much broader than that of intrinsic ones. Furthermore, an additional broad peak, the intensity of which is about 20% of the main peak, appears around 650 cm-1. The peak can be assigned to local vibrational modes of substitutional B and B-P pairs, B clusters, B-interstitial clusters, etc. in Si crystal. The Raman and X-ray photoelectron spectroscopic studies suggest that a crystalline shell heavily doped with these species is formed at the surface of a codoped Si nanocrystal and it induces the specific properties, i.e., hydrophilicity, high-stability in water, high resistance to hydrofluoric acid, etc. © 2014 AIP Publishing LLC.
2014, Journal of Applied Physics, 115 (8), 084301 - 084301, English[Refereed]
Scientific journal
© 2014 AIP Publishing LLC. Reversible emission evolution of thermally treated Ag activated zeolite Na-A upon dehydration/hydration in vacuum/water vapor was observed. The phenomenon was observed even for the sample with low Ag+-Na+ exchanging (8.3%), indicating that the emission from Ag activated zeolites may not come from Ag clusters while from the surrounding coordinated Ag+ ions or Ag0 atoms. It was disclosed that the characteristic yellow-green emission at ∼560±15nm is strongly associated with the coordinating water molecules to the Ag+ ions or Ag0 atoms, which is clear evidence for that the efficient emission from Ag activated zeolites may not originate from the quantum confinement effect.
2014, Applied Physics Letters, 105 (21), 1 - 4, English[Refereed]
Scientific journal
Photosensitization of europium (Eu) ions by silver (Ag) clusters was achieved by simultaneously doping Eu and Ag in zeolite cages. The photoluminescence (PL) due to the 5D0→ 7F2 transition of Eu ions at 613 nm is significantly increased by the presence of Ag clusters. The excitation wavelength dependence of the PL intensity coincided well with the absorption spectrum of Ag clusters, indicating that Eu ions are excited by the energy transfer from Ag clusters. © 2014 Elsevier B.V. All rights reserved.
2014, Optical Materials, 36 (5), 916 - 920, English[Refereed]
Scientific journal
We have investigated the structural, optical and ferromagnetic properties of undoped and Fe-doped TiO2 nanoribbons (NRbs) grown by a solvothermal method. A strong room temperature ferromagnetism (RTFM) is observed in both undoped and Fe-doped TiO2 NRbs. Fe-doped TiO2 NRbs exhibited a ∼4.8-fold enhancement in RTFM as compared to the undoped NRbs grown under similar conditions. However, the RTFM decreases at higher Fe concentration, possibly due to antiferromagnetic ordering between nearby Fe 3+ ions caused by a super exchange interaction. X-ray diffraction patterns reveal the pure TiO2(B) phase, the TiO2(B)- anatase mixed phase and the anatase-rutile mixed phase of the TiO2 structure. Field emission scanning electron microscopy and transmission electron microscopy observations reveal NRbs with uniform pore distribution and nanopits formed on the surface for both undoped and Fe-doped NRbs. These samples exhibit strong visible photoluminescence associated with oxygen vacancies and the ferromagnetic hysteresis loop, both of which are strongly enhanced after vacuum annealing. Optical absorption, electron spin resonance and x-ray photoelectron spectroscopic analyses are performed to elucidate the origin of RTFM. The observed RTFM in undoped and Fe-doped TiO2 NRbs is qualitatively explained through a model involving bound magnetic polarons, which include an electron locally trapped by an oxygen vacancy with the trapped electron occupying an orbital overlapping with the unpaired electron (3d1) of a Ti3+ ion and/or the unpaired electron (3d5) of a Fe 3+ ion. The development of TiO2 NRbs with tunable optical and magnetic properties constitutes an important step towards realizing improved magneto-optical and spintronic devices from novel TiO2 nanostructures. © 2014 IOP Publishing Ltd.
2014, Journal of Physics D: Applied Physics, 47 (23), 1 - 14, English[Refereed]
Scientific journal
Arrays of vertically aligned single crystalline Si nanowires (NWs) decorated with arbitrarily shaped Si nanocrystals (NCs) have been fabricated by a silver assisted wet chemical etching method. Scanning electron microscopy and transmission electron microscopy are performed to measure the dimensions of the Si NWs as well as the Si NCs. A strong broad band and tunable visible (2.2 eV) to near-infrared (1.5 eV) photoluminescence (PL) is observed from these Si NWs at room temperature (RT). Our studies reveal that the Si NCs are primarily responsible for the 1.5-2.2 eV emission depending on the cross-sectional area of the Si NCs, while the large diameter Si/SiOx NWs yield distinct NIR PL consisting of peaks at 1.07, 1.10 and 1.12 eV. The latter NIR peaks are attributed to TO/LO phonon assisted radiative recombination of free carriers condensed in the electron-hole plasma in etched Si NWs observed at RT for the first time. Since the shape of the Si NCs is arbitrary, an analytical model is proposed to correlate the measured PL peak position with the cross-sectional area (A) of the Si NCs, and the bandgap (Eg) of nanostructured Si varies as Eg = Eg (bulk) + 3.58 A-0.52. Low temperature PL studies reveal the contribution of non-radiative defects in the evolution of PL spectra at different temperatures. The enhancement of PL intensity and red-shift of the PL peak at low temperatures are explained based on the interplay of radiative and non-radiative recombinations at the Si NCs and Si/SiOx interface. Time resolved PL studies reveal bi-exponential decay with size correlated lifetimes in the range of a few microseconds. Our results help to resolve a long standing debate on the origin of visible-NIR PL from Si NWs and allow quantitative analysis of PL from arbitrarily shaped Si NCs. © 2014 IOP Publishing Ltd.
2014, Nanotechnology, 25 (4), 045703, English[Refereed]
Scientific journal
Strong and broad near infrared (NIR) emission peaked at ∼855nm upon optimal excitation at 342nm has been observed from molecule-like silver clusters (MLSCs) confined in zeolite A assisted by thermal activation. To the best of our knowledge, this is the first observation of NIR emission peaked at longer than 800nm from MLSCs confined in solid matrices. The decay time of the NIR emission is over 10 μs, which indicates that it is a spin-forbidden transition. The ∼855nm NIR emission shows strong dependence on the silver loading concentration and the thermal activation temperature. © 2014 AIP Publishing LLC.
2014, Journal of Applied Physics, 116 (1), 1 - 5, English[Refereed]
Scientific journal
We have investigated the microscopic origin of lattice expansion and contraction in undoped rutile TiO2 nanostructures by employing several structural and optical spectroscopic tools. Rutile TiO2 nanostructures with morphologies such as nanorods, nanopillars and nanoflowers, depending upon the growth conditions, are synthesized by an acid-hydrothermal process. Depending on the growth conditions and post-growth annealing, lattice contraction and expansion are observed in the nanostructures and it is found to correlate with the nature and density of intrinsic defects in rutile TiO2. The change in lattice volume correlates well with the optical bandgap energy. Irrespective of growth conditions, theTiO2 nanostructures exhibit strong near infrared (NIR) photoluminescence (PL) at 1.43 eV and a weak visible PL, which are attributed to the Ti interstitials and O vacancies, respectively, in rutile TiO2 nanostructures. Further, ESR study reveals the presence of singly ionized oxygen vacancy defects. It is observed that lattice distortion depends systematically on the relative concentration and type of defects such as oxygen vacancies and Ti interstitials. XPS analyses revealed a downshift in energy for both Ti 2p and O 1s core level spectra for various growth conditions, which is believed to arise from the lattice distortions. It is proposed that the Ti4+ interstitial and F+ oxygen vacancy defects are primarily responsible for lattice expansion, whereas the electrostatic attraction between Ti 4+ interstitial and O2- interstitial defects causes the lattice contraction in the undoped TiO2 nanostructures. The control of lattice parameters through the intrinsic defects may provide new routes to achieving novel functionalities in advanced materials that can be tailored for future technological applications. © 2014 IOP Publishing Ltd.
2014, Journal of Physics D: Applied Physics, 47 (21), 1 - 13, English[Refereed]
Scientific journal
The second-order nonlinearity of Si-rich SiNx thin films prepared by RF sputtering was investigated. It was found that the second-order nonlinear coefficient (deff) increases with increasing Si concentration in a wide range of Si concentrations. The observed maximum value of deff was 5.9 pm V -1, which is twice that of the β-BaB2O4 crystal. X-ray photoelectron spectroscopy analysis in the Si 2p energy region revealed that the films consist of Si species with different valence states. Strong correlation was observed between the deff values and the XPS peak intensity of Si 0 species, suggesting that Si clusters are the most probable origin of the large second-order nonlinearity. © 2014 IOP Publishing Ltd.
2014, Journal of Physics D: Applied Physics, 47 (21), 1 - 8, English[Refereed]
Scientific journal
We demonstrate graphene-assisted controlled fabrication of various ZnO 1D nanostructures on the SiO2/graphene substrate at a low temperature (540 C) and elucidate the growth mechanism. Monolayer and a few layer graphene prepared by chemical vapor deposition (CVD) and subsequently coated with a thin Au layer followed by rapid thermal annealing is shown to result in highly aligned wurtzite ZnO nanorods (NRs) with clear hexagonal facets. On the other hand, direct growth on CVD graphene without a Au catalyst layer resulted in a randomly oriented growth of dense ZnO nanoribbons (NRBs). The role of in-plane defects and preferential clustering of Au atoms on the defect sites of graphene on the growth of highly aligned ZnO NRs/nanowires (NWs) on graphene was established from micro-Raman and high-resolution transmission electron microscopy analyses. Further, we demonstrate strong UV and visible photoluminescence (PL) from the as-grown and post-growth annealed ZnO NRs, NWs, and NRBs, and the origin of the PL emission is correlated well with the X-ray photoelectron spectroscopy analysis. Our results hint toward an epitaxial growth of aligned ZnO NRs on graphene by a vapor-liquid-solid mechanism and establish the importance of defect engineering in graphene for controlled fabrication of graphene-semiconductor NW hybrids with improved optoelectronic functionalities. © 2013 American Chemical Society.
2014, ACS Applied Materials and Interfaces, 6 (1), 377 - 387, English[Refereed]
Scientific journal
A multi-shelled sphere with a quarter-wave thick shell is known to act as a spherical Bragg resonator with a complete photonic band gap and have potential applications in photonics. However, no fabrication techniques have been established. In this work, core-shell-shell particles with quarter-wave thick shells were synthesized by chemical solution processes for the first time. They consist of a Ce3+ doped Y2O3 nanoparticle core, a SiO2 first shell, and a Y2O3 second shell. The core and the second shell were fabricated by a homogeneous precipitation method and the first shell by a sol-gel method. By carefully optimizing the reaction conditions, the shell thickness was controlled to a quarter optical wavelength for visible (500 nm) light with the standard deviation of thickness of the order of several nanometers. The scattering and photoluminescence spectra of single particles were studied, and they were well reproduced by Mie theory. The results indicate that the luminescence properties of the nanoparticles can be modified by the quarter-wave thick shells. The procedures can be extended for the fabrication of multi-shelled photonic bandgap structures, by simply repeating the SiO2 and Y2O3 coating processes. © the Partner Organisations 2014.
2014, RSC Advances, 4 (61), 32293 - 32297, English[Refereed]
Scientific journal
In this work, we investigated the effects of europium doping on the second harmonic generation (SHG) of ZnO nanowires (NWs). A non-monotonic enhancement in the SHG is observed with the increase of the europium concentration. Maximum SHG is observed from the 1 at.% europium doped ZnO NWs with an enhancement factor of 4.5. To understand the underlying mechanism, the effective second order non-linear coefficient (deff) is calculated from the theoretical fitting with consideration of the absorption effect. Microstructural characterization reveals the structural deformation of the ZnO NWs caused by europium doping. We estimated the deviation in the crystal site symmetry around the Eu3+ ions (defined as the asymmetric factor) from photoluminescence measurement and it is found to be strongly correlated with the calculated deff value. A strong linear dependence between the magnitudes of deff and the asymmetric factor suggests that deviation in the local site symmetry of the ZnO crystal by europium doping could be the most probable origin of the observed large second order non-linearity. © 2014 IOP Publishing Ltd.
2014, Nanotechnology, 25 (22), 1 - 10, English[Refereed]
Scientific journal
Photosensitization of samarium (Sm) ions by silver (Ag) ions was achieved by simultaneously doping Sm and Ag in zeolite A cages. Photoluminescence (PL) from the 4G2/5G6H2/7 transition of Sm ions at 600nm was found to be more than 30 times enhanced by the presence of Ag ions. The excitation wavelength dependence of the PL intensity coincided well with the absorption spectra of Ag ions in the ultraviolet region, indicating that Sm ions are excited by the energy transfer from Ag ions. © 2014 The Japan Society of Applied Physics.
2014, Japanese Journal of Applied Physics, 53 (2 PART 1), 022102, English[Refereed]
Scientific journal
Near infrared (NIR) emission from the Nd3+ doped zeolite Y was strongly enhanced by partially vitrifying the zeolite structure via extra loading silver ions and post annealing. Under the low annealing temperatures at 450 C and 650 C, the states of the loaded silver were determined to be the co-existence of the isolated Ag0 atoms, the Ag+ ions, and the Ag2+ dimers. However, there was no enhancement in the NIR emission by the introduction of these small silver clusters. Under higher annealing temperature at 900 C where the lattice of the zeolite Y was partially collapsed into the amorphous phase, strong NIR emission enhancement at 1064 nm with a factor of 6.8 was observed. The partial vitrification process by the co-loading of silver and post heat-treatment had strong effect on eliminating the H2O molecules, which can greatly enhance the NIR emission. © 2014 AIP Publishing LLC.
2014, Journal of Applied Physics, 115 (3), 033507, English[Refereed]
Scientific journal
Si1-xGex alloy nanocrystals potentially have superior properties compared to Si nanocrystals such as an enhanced absorption cross-section and wider controllability of the band gap energy. However, reports on the synthesis of Si1-xGex alloy nanocrystals, especially colloidal Si1-xGex alloy nanocrystals, are still very limited and the quality is not as high as that of colloidal Si nanocrystals. Here, we report the development of a new type of luminescent colloidal Si1-xGex alloy nanocrystals of 3 to 6 nm in diameter. The characteristic feature of the Si1-xGex alloy nanocrystals is the formation of a high B and P concentration layer on the surface. The shell provides inorganic atomic ligands and B and P co-doped Si1-xGex nanocrystals can be dispersed in alcohol without any surface functionalization processes. This journal is © the Partner Organisations 2014.
2014, Journal of Materials Chemistry C, 2 (28), 5644 - 5650, English[Refereed]
Scientific journal
We report a novel method to prepare silicon quantum dots (Si-QDs) having excellent stability in water without organic-ligands by simultaneously doping phosphorus and boron. The codoped Si-QDs in water exhibit bright size-tunable luminescence in a biological window. The luminescence of codoped Si-QDs is very stable under continuous photoexcitation in water. © 2014 The Royal Society of Chemistry.
2014, Nanoscale, 6 (1), 122 - 126, English[Refereed]
Scientific journal
© 2014 Elsevier B.V. All rights reserved. Photoluminescence (PL) properties of silver (Ag) and dysprosium (Dy) codoped zeolites were investigated. It was found that PL from the 4F9/2-6H13/2 transition of Dy3+ ions at 575 nm is more than 50 times enhanced by the presence of Ag+ ions under ultraviolet excitation. The excitation wavelength dependence of the PL intensity coincided well with the absorption spectra of Ag+ ions, indicating that Dy3+ ions are excited by the energy transfer from Ag+ ions. In addition, by carefully optimizing annealing condition and Dy and Ag concentration, white light was realized due to the combination of blue emission of Ag+ ions, yellow emission of Dy3+ ions and red emission of Ag clusters.
2014, Optical Materials, 38, 75 - 79, English[Refereed]
Scientific journal
A novel approach has been developed for the realization of efficient near-infrared to near-infrared (NIR-to-NIR) upconversion and down-shifting emission in nanophosphors. The efficient dual-modal NIR-to-NIR emission is realized in a beta-NaGdF4/Nd3+@NaGdF4/Tm3+-Yb3+ core-shell nanocrystal by careful control of the identity and concentration of the doped rare earth (RE) ion species and by manipulation of the spatial distributions of these RE ions. The photoluminescence results reveal that the emission efficiency increases at least 2-fold when comparing the materials synthesized in this study with those synthesized through traditional approaches. Hence, these core-shell structured nanocrystals with novel excitation and emission behaviors enable us to obtain tissue fluorescence imaging by detecting the upconverted and down-shifted photoluminescence from Tm3+ and Nd3+ ions, respectively. The reported approach thus provides a new route for the realization of high-yield emission from RE ion doped nanocrystals, which could prove to be useful for the design of optical materials containing other optically active centers.
AMER CHEMICAL SOC, Feb. 2013, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 4 (3), 402 - 408, English[Refereed]
Scientific journal
Enhancement of upconversion luminescence by small assemblies of Au nanorods such as dimers, trimers, tetramers, etc, is studied by comparing upconversion images with electron microscope images. We show that small assemblies starting from dimers can enhance the upconversion luminescence, while isolated Au nanorods cannot. The analysis of the data reveals that the gaps between nanorods act as hot spots for the enhancement of upcnversion luminescence.
The Materials Research Society of Japan, 2013, Trans. Mat. Res. Soc. Japan, 38 (1), 131 - 134, EnglishTrue zero-order wave plates operating in the deep ultraviolet (DUV) range are produced from porous silica having very small in-plane optical anisotropy (refractive index anisotropy: ∼0.001). Small temperature (4.3×10 -5 λ/°C) and angle-dependent shifts of the retardance are obtained in the DUV range. The retardance shifts are 0.007λ and 0.035λ when the plate is tilted 15° on the [0 0 1] and [11̄0] axes, respectively. From the angle dependence, the shape of the refractive index ellipsoids is discussed. © 2012 Elsevier B.V.
2013, Optics Communications, 287, 137 - 139, English[Refereed]
Scientific journal
Upconversion photoluminescence (PL) of a composite nanoparticle consisting of an Er and Yb codoped NaYF4 core and a Au shell is studied theoretically and experimentally. We first investigate the effects of a Au shell on the radiative and nonradiative emission rates of a dipole placed in a core, the absorption and scattering cross sections of a composite nanoparticle, and the electric field within a core at the excitation wavelength. We then synthesize the composite nanoparticle and study the PL properties. From the analyses of the PL data in combination with the data obtained by theoretical calculations, the mechanism of the enhancement and quenching of upconversion PL by the formation of a Au shell is studied. © 2012 American Chemical Society.
2013, Journal of Physical Chemistry C, 117 (2), 1113 - 1120, English[Refereed]
Scientific journal
A terahertz (THz) wire-grid polarizer is fabricated by imprinting porous Si followed by oblique evaporation of Ag. We demonstrate that it works in a wide frequency region covering from 5 to 18 THz with the extinction ratio of 10 dB. The frequency region is much wider than that of THz wire-grid polarizers fabricated by conventional imprint lithography using organic materials. The result suggests that imprinting of porous Si is a promising fabrication technique to realize low-cost wire-grid polarizers working in the THz region. © 2013 Optical Society of America.
2013, Optics Letters, 38 (23), 5067 - 5070, English[Refereed]
Scientific journal
Second-order nonlinear optical properties of sputter-deposited Ge-doped SiO2 thin films were investigated. It was shown that the second-order nonlinearity of SiO2, which vanishes in the electric-dipole approximation due to the centrosymmetric structure, can be significantly enhanced by Ge doping. The observed maximum value of d33 was 8.2 pm/V, which is 4 times larger than d22 of β-BaB 2O4 crystal. Strong correlation was observed between the deff values and the electron spin resonance signals arising from GePb centers, suggesting that GePb centers are the most probable origin of the large second-order nonlinearity. © 2013 AIP Publishing LLC.
2013, Applied Physics Letters, 103 (20), 201117, English[Refereed]
Scientific journal
The radiative decay rate of a dipole emitter inside the core of a multi-layered dielectric sphere is theoretically investigated. It is shown that, when the thickness of each layer coincides with a quarter wavelength, the multi-layered sphere has a great potential to work as a three-dimensional photonic crystal with a high quality factor and a small mode volume. From the analysis of the dipole position dependence of a radiative decay rate, we show that a smaller core radius, a quarter wavelength at the smallest, is more suitable for real applications. The investigation on the tolerance for thickness nonuniformity reveals that the thickness variation of 10% is tolerable. © 2013 Optical Society of America.
2013, Optics Express, 21 (9), 10651 - 10658, English[Refereed]
Scientific journal
Photoluminescence (PL) properties of bismuth (Bi) doped porous silica thin films annealed at various temperatures and in different atmospheres were studied. The near infrared (NIR) luminescence depended strongly on the annealing atmosphere and temperature. To reveal the origin of the NIR luminescence, we performed comprehensive PL studies including steady state and time-resolved PL measurements at 8-300 K in wide excitation (250-500 nm) and detection (400-1550 nm) wavelength ranges. It was revealed that multiple Bi luminescence centers, such as Bi3+, Bi2+, Bi+, and Bi dimer, are stabilized in porous silica. © 2013 AIP Publishing LLC.
2013, Journal of Applied Physics, 114 (3), 033524 - 033524, English[Refereed]
Scientific journal
Bi-doped siliconoxynitride (SiON:Bi) thin films were prepared by a sputtering method and the photoluminescence (PL) properties were studied. Without any thermal treatments, broad Bi-related luminescence was observed in the near-infrared (NIR) range. The luminescence efficiency depended strongly on the film composition. It was found that N atoms play a crucial role for the formation of Bi NIR luminescence centers. The effect of annealing on the luminescence efficiency was also studied. The optimum annealing temperature to have the largest number of Bi NIR luminescence centers depended strongly on the film composition and it was lower for films with lower N concentration. The PL excitation spectra revealed that two different Bi NIR luminescence centers exist in the films. © 2013 Optical Society of America.
2013, Optics Letters, 38 (20), 4224 - 4227, English[Refereed]
Scientific journal
Despite decades of research on the role of intrinsic defects in enhancing the performance of reduced TiO2 based materials, unambiguous identification of defects responsible for visible light absorption, and near-infrared (NIR) photoluminescence from undoped TiO2 has remained challenging. Herein, through in situ photoluminescence (PL) studies under a controlled environment, we investigated the origin of an extended visible absorption, visible and NIR PL emission from undoped TiO2 nanoribbons grown by a solvothermal route. Our studies reveal that oxygen vacancies, Ti3+, and F+ center in TiO2 are responsible for absorption in the violet and blue-green region and the PL emission in the visible region. On the other hand, absorption in the yellow-red to NIR region and PL emission in the NIR region at 1.47 and ∼1.30 eV are due to Ti 4+ and Ti3+ interstitials, respectively, near the surface identified for the first time. The above conclusions are supported by electron paramagnetic resonance and X-ray photoelectron spectroscopy analyses. The development of such nanoporous undoped TiO2 nanoribbons with strong visible absorption and optical identification of Ti interstitial induced band gap states serves as an important milestone toward realizing improved visible light photocatalytic and photovoltaic applications of this novel material. © 2013 American Chemical Society.
2013, Journal of Physical Chemistry C, 117 (44), 23402 - 23411, English[Refereed]
Scientific journal
Upconversion photoluminescence (PL) properties of single Y 2O3 nanoparticles doped with Yb and Er (Y 2O3:Yb,Er) with a Ag over-layer is studied. We traced the PL and light scattering images of individual nanoparticles by changing the thickness of a Ag over-layer. When the Ag thickness is relatively small and only the upper part of a nanoparticle is covered by Ag (Ag half-shell), the PL is strongly enhanced. On the other hand, when the Ag thickness is increased and a continuous Ag over layer is formed, the enhancement factor decreases. From the correlation between the enhancement factors of the upconversion PL and scattering intensities as well as the change of the PL lifetime, the mechanism of the PL enhancement is discussed. © 2013 Elsevier B.V. All rights reserved.
2013, Optical Materials, 35 (12), 2394 - 2399, English[Refereed]
Scientific journal
We present a novel synthesis of ligand-free colloidal silicon nanocrystals (Si-NCs) that exhibits efficient photoluminescence (PL) in a wide energy range (0.85-1.8 eV) overcoming the bulk Si band gap limitation (1.12 eV). The key technology to achieve the wide-range controllable PL is the formation of donor and acceptor states in the band gap of Si-NCs by simultaneous doping of n- and p-type impurities. The colloidal Si-NCs are very stable in an ordinary laboratory atmosphere for more than a year. Furthermore, the PL spectra are very stable and are not at all affected even when the colloids are drop-cast on a substrate and dried in air. The engineering of the all-inorganic colloidal Si-NC and its optical data reported here are important steps for Si-based optoelectronic and biological applications. © 2013 American Chemical Society.
2013, Journal of Physical Chemistry C, 117 (22), 11850 - 11857, English[Refereed]
Scientific journal
In this work, we investigated the combined effects of Al doping and surface modification on the fabrication of a core-shell type ZnO/ZnS nanowires (NWs) and its structural, electrical, and photoluminescence (PL) properties. A systematic investigation for different concentrations of Al doping followed by surface modification with different thicknesses of ZnS layer was performed. Significant changes in the nature of PL spectra and electronic conductivity are observed and insight discussions are present. Structural characterization on the core-shell NWs reveals the successful fabrication of Al doped highly single crystalline ZnO core and polycrystalline ZnS shell with both ZnO and ZnS are of hexagonal wurtzite structure. Compared with the bare undoped ZnO NWs, Al doped core-shell ZnO/ZnS NWs exhibit two orders of magnitude improvement in the electronic conductivity and fivefold enhancement in the UV PL intensity. The Al doped core-shell ZnO/ZnS NWs shows an efficient improvement in the UV PL intensity than the undoped core-shell ZnO NWs. The obtained improvement in the PL result is explained on the basis of interfacial transfer of photogenerated charge carriers and modification of defects. © 2013 AIP Publishing LLC.
2013, Journal of Applied Physics, 114 (13), 134307, English[Refereed]
Scientific journal
We investigate the infrared-to-visible upconversion (UC) fluorescence properties of Bi-Er-Yb codoped zeolites. It is revealed that the UC emissions can be well controlled by the Yb3+ concentration in zeolites. By the addition of Yb3+, the green and red emissions are enhanced about 5 and 243 times, respectively. On the other hand, the intensity ratio of red-to-green is increased from 0.26 to 12.2. The tunable emission is due to the energy back transfer from Yb3+ to Er3+. It is expected that the achieved intense single band red emission may have potential application for in vivo bioimaging.
2013, Microporous and Mesoporous Materials, 173, 43 - 46, English[Refereed]
Scientific journal
The surface structure of P and B codoped colloidal Si-NCs are studied by photoluminescence (PL) in hydrofluoric acid (HF) solution and X-ray photoelectron spectroscopy (XPS). We find that codoped Si-NCs are much more stable in HF solution than undoped, P-doped, and B-doped Si-NCs. The PL study combined with XPS results reveal that a high B concentration layer is formed on the surface of codoped Si-NCs and the layer acts as a kind of inorganic atomic ligands for Si-NCs. The high B concentration layer makes Si-NCs hydrophilic and dispersible in polar liquids. Furthermore, the layer effectively protects Si-NCs from oxidation in solution and in air. © 2013 American Chemical Society.
2013, Journal of Physical Chemistry C, 117 (13), 6807 - 6813, English[Refereed]
Scientific journal
We report on the oxygen vacancy induced ferromagnetism (FM) at and above room temperature in undoped TiO2 nanoporous nanoribbons synthesized by a solvothermal route. The origin of FM in as-synthesized and vacuum annealed undoped nanoribbons grown for different reaction durations followed by calcinations was investigated by several experimental tools. X-Ray diffraction pattern and micro-Raman studies reveal the TiO2(B), TiO 2(B)-anatase, and anatase-rutile mixed phases of TiO2 structure. Field emission scanning electron microscopy and transmission electron microscopy observations reveal nanoribbons with uniform pore distribution and nanopits/nanobricks formed on the surface. These samples exhibit strong visible photoluminescence associated with oxygen vacancies and a clear ferromagnetic hysteresis loop, both of which dramatically enhanced after vacuum annealing. Direct evidence of oxygen vacancies and related Ti3+ in the as-prepared and vacuum annealed TiO2 samples are provided through X-ray photoelectron spectroscopy analysis. Micro-Raman, infrared absorption and optical absorption spectroscopic analyses further support our conclusion. The observed room temperature FM in undoped TiO2 nanoribbons is quantitatively analyzed and explained through a model involving bound magnetic polarons (BMP), which include an electron locally trapped by an oxygen vacancy with the trapped electron occupying an orbital overlapping with the unpaired electron (3d1) of Ti3+ ion. Our analysis interestingly shows that the calculated BMP concentration scales linearly with concentration of oxygen vacancies and provides a stronger footing for exploiting defect engineered ferromagnetism in undoped TiO2 nanostructures. The development of such highly porous TiO2 nanoribbons constitutes an important step towards realizing improved visible light photocatalytic and photovoltaic applications of this novel material. © 2013 The Royal Society of Chemistry.
2013, Nanoscale, 5 (12), 5476 - 5488, English[Refereed]
Scientific journal
Dynamics of quantized Auger recombination in Si1-xGex nanocrystals (NCs) embedded in SiO2 films was studied by femtosecond intraband pump-probe spectroscopy. The temporal change of the electron-hole pair number under strong photoexcitation was well explained by the quantized Auger recombination model that considered the size distribution of NCs. On the basis of the dependence of the Auger decay rate on temperature and Ge composition, we confirmed the occurrence of breakdown of the k-conservation rule in quantized Auger recombination in Si and Si1-xGex NCs.
AMER PHYSICAL SOC, Oct. 2012, PHYSICAL REVIEW B, 86 (15), English[Refereed]
Scientific journal
- 2012, Journal of Physical Chemistry C, 116 (33)
[Refereed]
Scientific journal
- 2012, Trans. Mater. Res. Soc. Jpn, 38, 449 - 452, EnglishEnhancement of upconversion Iuminescence of Al2O3 : Er3+, Yb3+ thin films by small assemblies of Au nanorods
[Refereed]
Scientific journal
We prepare Nd-Bi codoped zeolites by a method consisting of a simple ion-exchange process and subsequent high-temperature annealing. The emission covers the range of 970-1450 nm, corresponding to the electronic transitions of Nd 3+ ions and Bi-related active centers (BiRAC), respectively. The introduction of Bi distinctly broadens the excitation band of Nd 3+ in the visible region, and the lifetime of Nd 3+ reaches as long as 354 μs. In the zeolite matrix, Bi ions exist as BiRAC and Bi oxide agglomerates. The former one act as a sensitizer of Nd 3+ ions, and the latter one act as a blockage to avoid the quenching effect of coordinated water, which enable Nd 3+ ions to show efficient near-infrared (NIR) emission even the zeolites contain large amount of coordinated water. The excellent optical and structural properties make these NIR emitting nanoparticles promising in application as laser materials and biological probes. © 2011 Materials Research Society.
2012, Materials Research Society Symposium Proceedings, 1342, 61 - 66[Refereed]
International conference proceedings
Single dot spectroscopy of Si quantum dots (QDs) was performed by using surface plasmon polariton (SPP)-mediated excitation in the attenuated total reflection geometry with a MgF 2/Ag film on the base of a prism. Thanks to the 16 times enhancement of the incident electric field and very small background signal, PL from single Si QDs was observed clearly. This proves the usefulness of the technique for the detection of inherently weak emission of Si QDs. © 2011 Elsevier B.V. All rights reserved.
2012, Journal of Luminescence, 132 (5), 1157 - 1159, English[Refereed]
Scientific journal
The photoluminescence (PL) properties of P or B single-doped Si nanocrystals (Si-nc's) and P and B co-doped Si-nc's are studied. In the single-doped Si-nc samples, PL quenching occurs as a result of the Auger nonradiative recombination process between the photoexcited excitons and free carriers supplied by doped impurities. In the (P, B) co-doped sample, on the other hand, the donor-acceptor (D-A)-pair recombination emission is clearly observed on the long-wavelength side of the intrinsic Si-nc emission peak at ∼900 nm. The D-A-pair recombination energy is found to be smaller than the band-gap energy of bulk Si and is strongly dependent on the number of P and B impurities doped in a Si-nc. PL spectra are measured at 50 and 300 K and found to indicate that strong thermal quenching occurs in a (P, B) co-doped sample at 300 K. This quenching effect is probably because of carrier migration among the donor and acceptor states. The PL decay rate is determined as a function of the emitted-light wavelength for the pure and (P, B) co-doped Si-nc samples. © 2012 American Physical Society.
2012, Physical Review B - Condensed Matter and Materials Physics, 85 (4), 045441 - 045441, English[Refereed]
Scientific journal
Luminescence properties of Bi-doped oxidized porous silicon (OPS) thin films were studied. It was found that this material shows two broad luminescence bands centered at 845 nm with the FWHM of 120 nm and at 1410 nm with that of 220 nm under 488 nm excitation. A detailed analysis of the 3D plot of PL intensities versus excitation and emission wavelengths revealed that these luminescence bands arise from at least two different kinds of Bi luminescence centers. The broad luminescence covering the whole telecommunication window (1.2-1.6 μm) suggests that Bi-doped OPS thin films can be a candidate material for a broadband waveguide-type optical amplifier at optical telecommunication wavelengths. © 2012 Elsevier B.V. All rights reserved.
2012, Optical Materials, 34 (7), 1161 - 1164, English[Refereed]
Scientific journal
We investigate the effect of annealing atmosphere on the optical properties of Bi doped zeolites by diffuse reflectance, steady state and time-resolved photoluminescence (PL), and PL excitation measurements. The results reveal that zeolites can be used as an excellent host material to stabilize multiple Bi centers (Bi3+, Bi2+, and Bi-related near-infrared (NIR) active centers) in the framework, which shows ultra-broadband emission from visible to NIR range. Annealing in N2 leads to the partial conversion of Bi3+ ions into Bi2+ and Bi-related NIR active centers. Our results demonstrate that the broadband NIR emission may be attributed to the electronic transition of Bi low valence state, rather than a higher valence state. © 2011 Elsevier B.V. All rights reserved.
2012, Optical Materials, 34 (5), 821 - 825, English[Refereed]
Scientific journal
Electrochemical etching of a (110) oriented Si wafer results in a porous silicon (PSi) layer which exhibits a strong in-plane optical birefringence. We study the refractive index ellipsoid of (110) PSi by angle-resolved optical transmittance measurements and reveal that it is a biaxial crystal. The angle-resolved transmission electron microscope observations demonstrate that pores grow along the directions in between the 100 crystal axes and the etching current flow and these directions depend on the etching current density. The etching current density dependence of the pore direction indicates that the shape of the index ellipsoid can be controlled by the etching condition. © 2012 American Institute of Physics.
2012, Journal of Applied Physics, 111 (8), 1 - 6, English[Refereed]
Scientific journal
Nonlinear optical responses of boron (B)-doped silicon nanocrystals (Si-ncs) embedded in borosilicate glass were studied by z-scan and optical Kerr gate methods under femtosecond excitation at 780 nm. The nonlinear refractive index (n2) and the two photon absorption coefficients (β) of B-doped Si-ncs were found to be 3 times enhanced, compared to those of intrinsic Si-ncs. The response time was faster than 100 fs even at 5 K. The origin of the large nonlinear optical response was discussed, based on the experimental data of n2, electron spin resonance spectra, and linear absorption spectra. © 2012 Optical Society of America.
2012, Optics Letters, 37 (11), 1877 - 1879, English[Refereed]
Scientific journal
Nonlinear optical responses of phosphorus and boron codoped and compensated silicon quantum dots (Si-QDs) embedded in borophosphosilicate glass were studied by a z-scan and an optical Kerr gate methods under femtosecond excitation at 780 nm. The nonlinear refractive index (n 2) and the two photon absorption coefficients (β) of compensated Si-QDs were found to be enhanced several times compared to those of intrinsic Si-QDs. The response time was shorter than our time resolution of 100 fs at room temperature. © 2012 American Institute of Physics.
2012, Applied Physics Letters, 101 (4), 1 - 3, English[Refereed]
Scientific journal
Metal-insulator-metal (MIM) microcavities consisting of a layer of polyvinyl alcohol doped and undoped with cyanine dye molecules were prepared and their reflection and transmission spectra were measured. In the doped-MIM microcavity, dispersion curves determined from the reflection data clearly showed the anticrossing behavior arising from the strong coupling between excitons in the dye molecules and photonic modes supported by the MIM microcavity. The experimental dispersion curves could be well reproduced by a standard expression of the coupled mode dispersions by appropriately taking into account the plasmonic nature of the transverse magnetic mode supported by the MIM microcavity. A large splitting between the transverse electric and transverse magnetic modes in the upper branch of the coupled modes can also be well explained by the plasmonic effects. © 2012 American Physical Society.
2012, Physical Review B - Condensed Matter and Materials Physics, 86 (4), 1 - 8, English[Refereed]
Scientific journal
Bi 5(GaCl 4) 3 sample has been synthesized through the oxidation of Bi metal by gallium chloride (GaCl 3) salt. Powder X-ray diffraction as well as micro-Raman scattering results revealed that, in addition to crystalline Bi 5(GaCl 4) 3 in the product, an amorphous phase containing [GaCl 4] - and [Ga 2Cl 7] - units also exists. The thorough comparison of steady-state and time-resolved photoluminescent behaviors between the Bi 5(GaCl 4) 3 product and Bi 5(AlCl 4) 3 crystal leads us to conclude that Bi 53+ is the dominant emitter in the product, which gives rise to the ultrabroad emission ranging from 1 to 2.7 μm. Detailed quantum chemistry calculation helps us assign the observed excitations to some electronic transitions of the Bi 53+ polycation, especially at shorter wavelengths. It is believed that our work shown here is not only helpful to solve the confusions on the luminescent origin of bismuth in other material systems, but also serves to develop novel broadband tunable laser materials. © 2012 The Royal Society of Chemistry.
2012, Dalton Transactions, 41 (36), 11055 - 11061, English[Refereed]
Scientific journal
We demonstrate the formation of a new type of surfactant-free colloidal silicon nanocrystal (Si-NC). The characteristic structural feature of the Si-NCs is simultaneous doping of phosphorus (P) and boron (B) in and on the surface of Si-NCs. The codoped Si-NCs are stable in methanol for more than a year and exhibit luminescence in the near-infrared range. We perform comprehensive studies on the structure of codoped colloidal Si-NCs and discuss the mechanism of the high solution dispersibility. © 2012 American Chemical Society.
2012, Journal of Physical Chemistry C, 116 (33), 17969 - 17974, English[Refereed]
Scientific journal
For the first time, we report that a single crystal of (K-crypt) 2Bi2 containing [Bi2]2- displays ultra-broad near-infrared photoluminescence (PL) peaking at around 1190 nm and having a full width at the half maximum of 212 nm, stemming from the inherent electronic transitions of [Bi2]2-. The results not only add to the number of charged Bi species with luminescence, but also deepen the understanding of Bi-related near-infrared emission behavior and lead to the reconsideration of the fundamentally important issue of Bi-related PL mechanisms in some material systems such as bulk glasses, fibers, and conventional optical crystals. © 2012 The Royal Society of Chemistry.
2012, Journal of Materials Chemistry, 22 (38), 20175 - 20178, English[Refereed]
Scientific journal
We report the observation of near-infrared photoluminescence from Te 4(Ga2Cl7)2 and Te 4(Al2Cl7)2 molecular crystals containing Te42+ polycations. The experimental and theoretical results clearly revealed that the Te42+ polycation is a smart near-infrared emitter with characteristic emission peaks at 1252 and 1258 nm for Te4(Ga2Cl7)2 and Te4(Al2Cl7)2 crystals, respectively, resulting from the intrinsic electronic transitions of Te 42+. Furthermore, it was also found that the emissions strongly depend on the excitation wavelengths for both Te4(Ga 2Cl7)2 and Te4(Al2Cl 7)2 samples, most possibly due to the co-existence of other Te-related optically active centers. This research not only enriches the species of luminescent charged p-block element polyhedra and deepens the understanding of Te-related photophysical behaviors, but also may stimulate efforts for designing novel material systems using such active centers. It is also greatly expected that these sub-nanometer optically active species could exist in other systems such as glasses, polymers, and bulk optical crystals, and the stabilization of these centers in widely used hosts will pave the way for their practical applications. © The Royal Society of Chemistry 2012.
2012, Journal of Materials Chemistry, 22 (47), 24792 - 24797, English[Refereed]
Scientific journal
Multilayer structures consisting of bismuth (Bi)-doped silica thin films and different kinds of spacer, i.e., Si, silica, Si-rich silica, layers are grown and the luminescence properties are studied. When samples were annealed at a low temperature, Bi-related near infrared active centers (BRACs) were formed at interfaces between Bi-doped silica and Si-rich silica (or silicon) due to the reduction of Bi 3+ to BRACs by silicon. On the other hand, films annealed at a high temperature showed similar emission behaviors to bulk glasses. The results demonstrated here establish a new strategy for the control of BRACs and building peculiar Bi activated film structures. © 2012 American Institute of Physics.
2012, Journal of Applied Physics, 112 (7), 1 - 4, English[Refereed]
Scientific journal
Dynamics of quantized Auger recombination in Si 1-xGe x nanocrystals (NCs) embedded in SiO 2 films was studied by femtosecond intraband pump-probe spectroscopy. The temporal change of the electron-hole pair number under strong photoexcitation was well explained by the quantized Auger recombination model that considered the size distribution of NCs. On the basis of the dependence of the Auger decay rate on temperature and Ge composition, we confirmed the occurrence of breakdown of the k-conservation rule in quantized Auger recombination in Si and Si 1-xGe x NCs. © 2012 American Physical Society.
2012, Physical Review B - Condensed Matter and Materials Physics, 86 (15), 1 - 5, English[Refereed]
Scientific journal
Nonlinear optical responses of bismuth (Bi) doped silicon-rich silicon dioxide (Si-rich SiO 2) films were studied by a z-scan and an optical Kerr gate method under femtosecond excitation around 800 nm. It was found that the Bi-doping enhances the nonlinear optical response of Si-rich SiO 2 films by several orders of magnitudes. The nonlinear refractive index was of the order of 10 -11 cm 2 / W and the response time was shorter than our time resolution of 100 fs. The nonlinear refractive index was independent of the wavelength in the range from 750 to 835 nm, suggesting that virtual transitions are involved in the nonlinear optical processes. © 2012 American Institute of Physics.
2012, Applied Physics Letters, 101 (19), 1 - 4, English[Refereed]
Scientific journal
Nd-Bi codoped zeolites were prepared by an ion-exchange process, and the optical properties were investigated by photoluminescence (PL) and PL excitation spectra, and decay time measurements. The results show that the NIR emission of Nd(3+) ions is significantly enhanced by the introduction of bismuth in codoped samples, and the lifetime reaches 246 mu s. It is also observed that NIR-active Bi acts as a sensitizer of Nd(3+) ions. The energy transfer efficiency is also estimated. The peculiar optical properties make Nd-Bi codoped zeolites promising for potential application in biological probes. (C) 2011 Optical Society of America
OPTICAL SOC AMER, 2011, Optics Letters, 36 (6), 1017 - 1019, English[Refereed]
Scientific journal
Absorption and surface-enhanced Raman scattering (SERS) spectra of size-selected C8H2 adsorbed on Ag colloids were investigated. The Ag colloids after C8H2 adsorption are stable without precipitation of Ag nanoparticle aggregates. The spectra strongly depend on the C8H2 concentration. A good correlation between the concentration dependence of the absorption spectrum and that of SERS intensities supports the electromagnetic mechanism of SERS. The use of size-selected C8H2 made it possible to demonstrate also the chemical effects, which manifest themselves in the differences in the positions of SERS bands for different SERS enhancers, i.e., Ag colloid and Ag island film. © 2010 Elsevier B.V. All rights reserved.
2011, Chemical Physics Letters, 503 (1-3), 118 - 123, English[Refereed]
Scientific journal
The combined advantages of bismuth and aluminosilicates lead to a new type of nanosized biolabel. The near-infrared (NIR)-emitting silica-coated bismuth-doped aluminosilicate nanoparticles are simple to prepare and exhibit a broad excitation band in the first biological window, efficient long-lived photoluminescence (PL) covering the second window, high photostability, low cytotoxicity, and easy penetration into living tissues. In vivo PL bioimaging and decay are tested in living mice. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
2011, Small, 7 (2), 199 - 203, English[Refereed]
Scientific journal
We have shown that Lewis-acidic halogenoaluminate ionic liquid (IL) containing subvalent bismuth can be used as a near-IR (NIR) luminescent material. Raman and absorption spectra evidence the coexistence of Bi 53+ and Bi+ in the liquid. The Bi 53+ and Bi+ emitters, stabilized by this Lewis-acidic liquid, demonstrate ultrabroad NIR photoluminescence with a lifetime of around 1 μs. We envisage that the bismuth activated ILs would not only enrich the well-established spectrum of soft luminescent materials but also might promote the design of novel photonic materials activated by other p-block elements. © 2011 Optical Society of America.
2011, Optics Letters, 36 (2), 100 - 102, English[Refereed]
Scientific journal
We present a method for the formation of noble metal nanoparticle ensembles in nanostructured silicon. The key idea is based on the unique property of the large reduction potential of extended internal hydrogen-terminated porous silicon surfaces. The process of metal nanoparticle formation in porous silicon was experimentally traced using their optical plasmon resonance response. We also demonstrate that bimetallic compounds can be formed in porous silicon and that their composition can be controlled using this technique. Experimental results were found to contradict partially with considerations based on Mie theory. © 2011 American Institute of Physics.
2011, Applied Physics Letters, 98 (1), English[Refereed]
Scientific journal
The Bi5(AlCl4)3 crystal, synthesized by a environmentally friendly room-temperature method using ionic liquids as reaction solvents, exhibits extremely broad near-infrared photoluminescence (PL) with a full width at the half maximum (FWHM) of >510 nm and an effective PL lifetime of 4.1 s at 1160 nm. We envision that this study not only extends the understanding of photophysical properties of materials containing subvalent bismuth, but also may have promise for the design of novel photonic materials containing a wide array of p-block elements. © 2011 The Royal Society of Chemistry.
2011, Journal of Materials Chemistry, 21 (12), 4060 - 4063, English[Refereed]
Scientific journal
Thin films consisting of the layers of phosphorus (P) and boron (B) co-doped Si nanocrystals (Si-ncs) and glass spacer layers were prepared and their photoluminescence properties were studied. Cross-sectional TEM observations revealed the growth of Si-ncs with narrow size distributions. The samples exhibited PL below the band gap energy of bulk Si crystal at room temperature. The low-energy PL is considered to arise from the transitions between donor and acceptor states in compensated Si-ncs. The successful formation of narrow size distribution co-doped Si nanocrystals promotes the study of the optical properties of compensated Si nanocrystals. © 2010 Elsevier B.V. All rights reserved.
2011, Journal of Luminescence, 131 (5), 1066 - 1069, English[Refereed]
Scientific journal
Nd-Bi codoped zeolites were prepared by an ion-exchange process, and the optical properties were investigated by photoluminescence (PL) and PL excitation spectra, and decay time measurements. The results show that the NIR emission of Nd3+ ions is significantly enhanced by the introduction of bismuth in codoped samples, and the lifetime reaches 246 μs. It is also observed that NIR-active Bi acts as a sensitizer of Nd3+ ions. The energy transfer efficiency is also estimated. The peculiar optical properties make Nd-Bi codoped zeolites promising for potential application in biological probes. © 2011 Optical Society of America.
2011, Optics Letters, 36 (6), 1017 - 1019, English[Refereed]
Scientific journal
Yb-Bi co-doped zeolites are prepared by a method consisting of a simple ion-exchange process and subsequent high-temperature annealing. We observe two strong near-infrared (NIR) emission bands overlapping in the range 930-1480 nm, corresponding to the electronic transitions of bismuth-related active centres (BiRAC) and Yb3+ ions, respectively. In the obtained products, the excitation wavelength of Yb3+ is extended to the range 420-850 nm, and the lifetime reaches 665 μs. In the zeolite matrix, Bi ions exist as BiRAC and Bi compound agglomerates. The former act as a sensitizer of Yb 3+ ions, and the latter act as a blockage to seal the pores of zeolites, which enables Yb3+ ions to show efficient NIR emission even if the zeolites contain a large amount of coordinated water. The excellent optical and structural properties make these NIR-emitting nanoparticles promising in applications as biological probes. © 2011 IOP Publishing Ltd.
2011, Journal of Physics D: Applied Physics, 44 (15), 155101, English[Refereed]
Scientific journal
Composite films of poly(vinyl alcohol) containing polyynes adsorbed on aggregates of Ag nanoparticles were prepared and the stability of the Ag aggregates and polyynes was investigated by measuring the time evolution of absorption and surface-enhanced Raman spectra. The results indicate that the embedded aggregates of Ag nanoparticles and adsorbed polyynes are stable for a month. The high stability of the composite films made it possible to obtain an excitation profile of the surface-enhanced Raman spectrum. The excitation profile could be well reproduced by a theoretical calculation based on the electromagnetic mechanism of surface-enhanced Raman scattering. © 2011 Elsevier Ltd. All rights reserved.
2011, Carbon, 49 (14), 4704 - 4709, English[Refereed]
Scientific journal
Thin films of aligned nanowires composed of oriented para-sexiphenyl molecules were prepared on muscovite mica substrates and transferred to the surfaces of Ag films. Results of attenuated total reflection (ATR) measurements on these samples with a fixed wavelength of incident light clearly demonstrate the anisotropic propagation of surface plasmon polaritons (SPPs) induced by the optical anisotropy in the nanowire films. The magnitude of the SPP wave vector takes a maximum value when the SPP propagates along the direction of molecular orientation. Results of ATR measurements performed for various wavelengths of the incident light reveal the anisotropy in the SPP dispersion curve in a wide range of photon energy. From the fitting of theoretical reflection curves to observed ATR spectra, dispersions of the principal values of dielectric tensor of the nanowire film are obtained. © 2011 American Physical Society.
AMER PHYSICAL SOC, 2011, Physical Review B - Condensed Matter and Materials Physics, 84 (8), English[Refereed]
Scientific journal
Porous Si made from d110T Si wafers exhibits strong in-plane optical anisotropy (birefringence) in the visible and near-IR ranges. Oxidation of the birefringent porous Si results in the formation of birefringent porous silica. We demonstrate that the degree of the birefringence of porous silica can be controlled by the oxidation condition, and very small birefringence can be achieved. The smallest anisotropy of the refractive index (Δn) is 0.001, which is about ten times smaller than that of quartz. The small birefringence allows us to produce true zero-order wave plates operating in the UV range. © 2011 Optical Society of America.
2011, Optics Letters, 36 (19), 3951 - 3953, English[Refereed]
Scientific journal
Si nanocrystals (Si-NCs) dispersible in polar liquid without surface functionalization by organic molecules have been realized by simultaneously doping n and p type impurities. We show that the codoped Si-NCs are stable in methanol for more than five months, while intrinsic Si-NCs prepared by the same procedure form large agglomerates. The different behavior of the intrinsic and codoped Si-NCs in solutions suggests that doped impurities exist on the surface of Si-NCs and the surface potential is large enough to prevent the agglomeration. The colloidal solution of codoped Si-NCs exhibits broad photoluminescence with the maximum in the near infrared range (1:1-1:3 eV). © 2011 Optical Society of America.
2011, Optics Letters, 36 (20), 4026 - 4028, English[Refereed]
Scientific journal
Optical transitions in silicon nanocrystals with different surface passivations were probed at low temperatures on a single-particle level. A type of quasidirect recombination process, different from the quantum-confined exciton transition, is identified. The luminescence spectra have different emission energies, but the contribution of a no-phonon transition is significantly higher than expected from the quantum-confinement model. Its relative strength was found to be temperature dependent, suggesting spatial localization of excitons as a possible origin. © 2011 American Physical Society.
2011, Physical Review B - Condensed Matter and Materials Physics, 84 (12), English[Refereed]
Scientific journal
Boron (B) doped Si nanocrystals (Si-ncs) dispersed in hydrofluoric (HF) acid solution are prepared by dissolving borosilicate films containing B-doped Si-ncs in HF solution. We find that the etching rate of B-doped Si-ncs is much smaller than that of undoped Si-ncs. The difference of the etching rate allows us to extract only doped Si-ncs in the mixture of doped and undoped Si-ncs and observe the photoluminescence (PL) due to the transition from the conduction band to the acceptor state. The PL was very broad with the maximum around 1.15 eV. From the analysis of the PL data obtained for the samples prepared under different conditions and different etching time, preferential doping sites of B atoms are estimated. The data suggests that B-doped Si-ncs consists of intrinsic cores and heavily B-doped shells. © 2011 American Institute of Physics.
2011, Journal of Applied Physics, 110 (6), 063528 - 063528, English[Refereed]
Scientific journal
Developing Si compatible optical sources has attracted a great deal of attention owing to the potential for forming inexpensive, monolithic Si-based integrated devices. In this Letter, we show that ultra broadband near-IR (NIR) luminescence in the optical telecommunication window of silica optical fibers was obtained for Bi-doped siliconrich silica films prepared by a co-sputtering method. Without excess Si, i.e., Bi-doped pure silica films, no luminescence was observed in the NIR range. A broad Bi-related NIR photoluminescence appears when excess Si was doped in the Bi-doped silica. The luminescence properties depended strongly on the amount of excess Si and the annealing temperature. Photoluminescence results suggest that excess Si acts as an agent to activate Bi NIR luminescence centers and also as an energy donor to transfer excitation energy to the centers. It is believed that this peculiar structure might find some important applications in Si photonics. © 2011 Optical Society of America.
2011, Optics Letters, 36 (21), 4221 - 4223, English[Refereed]
Scientific journal
Ultraviolet-blue to near-infrared (NIR) downconversion is investigated for the Dy3+-Yb3+ couple in zeolites by steady-state and time-resolved photoluminescence (PL) spectra, and PL excitation spectra. Upon excitation of the 4F9/2 level of Dy3+, NIR quantum cutting could occur through a two-step energy transfer from one Dy 3+ ion to two neighbouring Yb3+ ions via an intermediate level. The energy transfer efficiency from the 4F9/2 level is estimated to be 42%, and the intrinsic PL quantum efficiency of Yb 3+ emission reaches 54%. The findings may have potential application in enhancing the energy efficiency of silicon-based solar cells. © 2011 IOP Publishing Ltd.
2011, Journal of Physics D: Applied Physics, 44 (45), 455301, English[Refereed]
Scientific journal
A series of Bi doped zeolites are prepared by an ion-exchange process by changing doping concentration in a wide range, and the optical properties are investigated. The near-infrared photoluminescence (PL) intensity, full width at half maximum and decay time depend strongly on Bi doping concentration. The PL intensity increases 178 times when the concentration is changed from 0.3 to 1.5 at. %. At the same time, the lifetime increases from 83 to 527 μs. The results prove the model that doped Bi acts not only as optically active centers, but also as pore-sealing substances to isolate the centers. The comparison of PL and Raman data suggests that in addition to previously proposed Bi 2O3, other Bi-related materials, probably Bi metal, play an important role to isolate the active centers. © 2011 Elsevier Inc. All rights reserved.
2011, Microporous and Mesoporous Materials, 145 (1-3), 21 - 25, English[Refereed]
Scientific journal
We have shown that tunable and highly efficient broadband near-IR (NIR) luminescence can be realized in erbium/bismuth codoped zeolites. The emission covers the ranges of 930-1450 nm and 1450-1630 nm. The intensity ratio of the two bands can be tuned by adjusting the concentration of erbium and the excitation wavelength. Steady-state and time-resolved photoluminescence (PL), and PL excitation measurements indicate that two kinds of emitters coexist in the pores of zeolites, and that NIR active bismuth simultaneously acts as a sensitizer of erbium. The present results demonstrate an important rational strategy for the design of a tunable NIR-emitting zeolite-based nanosystem. (C) 2010 Optical Society of America
OPTICAL SOC AMER, 2010, Optics Letters, 35 (11), 1926 - 1928, English[Refereed]
Scientific journal
- Silicon Nanocrystals: Fundamentals, Synthesis and Applications, 2010, Silicon Nanocrystals: Fundamentals, Synthesis and Applications, 43 - 68
[Refereed]
Scientific journal
Porous silicon-based rugate filters operating in the mid-infrared spectral range are fabricated by electrochemical etching of bulk silicon wafers. The rugate filter has a high reflectivity stop-band at 5 μm with no higher-order harmonics and very small sidelobes. Furthermore, broadband high pass filter having the cutoff wavelength in a mid-infrared range is demonstrated by combining five rugate structures. © 2010 Elsevier B.V. All rights reserved.
2010, Infrared Physics and Technology, 53 (4), 292 - 294, English[Refereed]
Scientific journal
Ultrabroadband near-IR (NIR) emission has been realized in bismuth-embedded sodalite nanocrystals. Steady-state and time-resolved photoluminescence and Raman results suggest that Bi+ active centers contribute to the NIR emission. This study demonstrates that sodalite nanocrystals can serve as excellent hosts for bismuth NIR active centers, thus paving the way for their wide applications in nanophotonics. © 2010 Optical Society of America.
2010, Optics Letters, 35 (11), 1743 - 1745, English[Refereed]
Scientific journal
Temperature dependence of the in-plane optical anisotropy of birefringent porous Si produced from a (110) Si wafer is studied. The anisotropy of refractive indices in the [001] and [1 1- 0] directions increased about 0.3% when the temperature rose from 30 to 100°C. The effective medium approximation could reproduce the experimental result in the low temperature range, while discrepancy appeared at high temperatures. The discrepancy suggests that the structural anisotropy of porous Si starts to relax at relatively low temperatures. © 2010 American Institute of Physics.
2010, Applied Physics Letters, 96 (24), English[Refereed]
Scientific journal
We show that sensitized superbroadband near-IR (NIR) emission in bismuth glass/Si nanocrystal superlattices can be realized. Photoluminescence is enhanced by 1 order of magnitude in this structure. We observed that the excitation wavelength dependence of the NIR emission does not show any distinct structure corresponding to the direct transition of bismuth IR-active centers. Our results suggest that the enhanced emission might result from the energy transfer from Si nanocrystals to IR-active bismuth. This structure may find broad applications for broadband amplifiers and broadly tunable laser sources. © 2010 Optical Society of America.
2010, Optics Letters, 35 (13), 2215 - 2217, English[Refereed]
Scientific journal
We have shown that tunable and highly efficient broadband near-IR (NIR) luminescence can be realized in erbium/bismuth codoped zeolites. The emission covers the ranges of 930-1450 nm and 1450-1630 nm. The intensity ratio of the two bands can be tuned by adjusting the concentration of erbium and the excitation wavelength. Steady-state and time-resolved photoluminescence (PL), and PL excitation measurements indicate that two kinds of emitters coexist in the pores of zeolites, and that NIR active bismuth simultaneously acts as a sensitizer of erbium. The present results demonstrate an important rational strategy for the design of a tunable NIR-emitting zeolite-based na-nosystem. © 2010 Optical Society of America.
2010, Optics Letters, 35 (11), 1926 - 1928, English[Refereed]
Scientific journal
Photoluminescence spectra of a dye layer placed at the middle of a metal-insulator-metal (MIM) structure are measured and compared with those of a reference sample without metallic layers. The observed spectra are much sharper than those of the reference sample and the peak wavelength shifts to shorter wavelengths as the observation angle increases. Furthermore, the enhancement in both the emission intensity and power is clearly observed. Electromagnetic calculations based on a point dipole model indicate that the observed light emission is mediated by radiative surface-plasmon polaritons and lowest-order transverse electric modes supported by the MIM structure. The observed enhancement is thought to result from a combination of the enhanced spontaneous emission rate and concentration of radiation intensities in a relatively narrow wavelength region brought by the MIM structure. © 2010 The American Physical Society.
2010, Physical Review B - Condensed Matter and Materials Physics, 82 (3), English[Refereed]
Scientific journal
The radial distribution of electrically active B in individual in situ B-doped Si nanowires (SiNWs) grown by the vapor liquid solid (VLS) process is studied by combining micro-Raman spectroscopy and wet chemical etching. The etching of the surface layer results in significant changes in the Raman spectra; Fano-type asymmetry, which is a characteristic of heavily doped p-type Si, disappears and the spectra become almost symmetric. The Raman data reveal that the as-grown B-doped SiNWs consist of a heavily B-doped shell and an almost intrinsic core. © 2010 The Japan Society of Applied Physics.
2010, Japanese Journal of Applied Physics, 49 (8 PART 1), English[Refereed]
Scientific journal
Bismuth embedded Y zeolites were studied by using UV-vis- near infrared (NIR) diffuse reflectance, Raman, and steady-state NIR photoluminescence spectroscopy. The results suggest that Bi53+ and Bi + active centers coexist in the dehydrated and hydrated zeolite framework, both of which contribute to NIR emission. Furthermore, it was revealed that the high-temperature annealing leads to the formation of Bi 2 O3 clusters, which act as blocks for selectively closing down the "n-out windows" of H2 O and O2 molecules in the zeolites. It is believed that these materials can find a wide array of applications as active media of broadly tunable micro or nano-optical sources. © 2010 American Institute of Physics.
2010, Applied Physics Letters, 97 (13), English[Refereed]
Scientific journal
Comprehensive studies on nonlinear refractive indices (n2) of SiO2 films containing Si nanocrystals and/or nanoclusters (SiO 2:Si-ncs) are performed. The comparison of the nonlinear refractive indices with the electron spin resonance signals reveals that defect states play a major role in the large n2 when the annealing temperature is low, i.e., when Si nanoclusters exist in films. On the other hand, when Si nanocrystals are grown by high-temperature annealing, the contribution of defect states becomes small and that of the quantized electronic states of Si nanocrystals becomes large. The present results demonstrate that both the defect states and the quantized electronic states should be taken into account to explain the origin of large n2 of SiO2:Si-ncs and to optimize the structure to maximize n2. © 2010 American Institute of Physics.
2010, Journal of Applied Physics, 108 (6), English[Refereed]
Scientific journal
Comprehensive studies have been performed on the nonlinear optical responses of silica films containing phosphorus (P)-doped Si nanoclusters and/or nanocrystals. In P-doped Si nanocrystals, enhancements of the nonlinear refractive indices (n2) and two photon absorption coefficients (β) relative to those of intrinsic Si nanocrystals were observed. The analysis of electron spin resonance and absorption spectra revealed that P donors are responsible for the large enhancements of n2 and β. © 2010 IOP Publishing Ltd.
2010, Journal of Physics D: Applied Physics, 43 (50), English[Refereed]
Scientific journal
We have shown that efficient superbroadband near-IR luminescence can be realized in bismuth-doped high-silica nanocrystalline zeolites. The emission band covered the range of 930-1620 nm, with a maximum peak at 1146.3 nm, an FWHM of 152 nm, and a lifetime of over 300 mu s under the excitation of a 488 nm laser line. The observed luminescence was attributed to subvalent Bi (Bi(+)) ions formed in the annealed zeolites. These Bi-doped nanozeolites may find applications as superbroadband near-IR nano-optical sources. (C) 2009 Optical Society of America
OPTICAL SOC AMER, 2009, Optics Letters, 34 (8), 1219 - 1221, English[Refereed]
Scientific journal
Significantly enhanced superbroadband near infrared emission has been realized in bismuth/aluminum doped high-silica zeolite derived nanoparticles. The emission intensity can be easily tailored by the introduction of aluminum. The luminescence lifetime can reach up to 695 mu s. The results reveal that the existence of charge imbalance environment caused by [AlO4/2](-) units in host materials is requisite to the formation of infrared-active Bi+. The finding presents a feasible route to design high-efficient bismuth activated infrared luminescent nanoparticles. These bismuth doped nanoparticles may find applications as superbroadband near infrared nano optical sources. (C) 2009 Optical Society of America
OPTICAL SOC AMER, 2009, Optics Express, 17 (8), 6239 - 6244, English[Refereed]
Scientific journal
Hong-Tao Sun, Akinobu Hosokawa, Yuji Miwa, Fumiaki Shimaoka, Minoru Fujii, Minoru Mizuhata, Shinji Hayashi, Shigehito Deki, 2009, 'ChemInform Abstract: Strong Ultra-Broadband Near-Infrared Photoluminescence from Bismuth-Embedded Zeolites and Their Derivatives.', <i>ChemInform</i>, vol. 40, no. 47
2009, ChemInform, 40 (47)[Refereed]
Zeolites with embedded bismuth compounds display strong, air-stable, long-lived, ultrabroadband, and tunable near-infrared photoluminescence (see picture). Bismuth ions not only act as luminescence-active centers, but also as blocks for selectively closing the "in-out windows" of water molecules. Bismuth active centers can be sealed in a low-vibrational environment by bismuth agglomerates even when the sample still contains a large amount ofwater. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.
2009, Advanced Materials, 21 (36), 3694 - +[Refereed]
Scientific journal
The electronic excitation energy transfer between excitons in silicon nanocrystal assemblies and iodine molecules in an organic solution is studied. From the time-resolved photoluminescence the rate of the energy transfer is found to increase with approaching a wavelength region, where the photoluminescence spectrum of nanocrystals overlaps the absorption spectrum of iodine molecules, and with increasing the radiative recombination rate of nanocrystals. The energy-transfer rate is also found to depend on the concentration of iodine molecules. This dependence is well explained by Förster-type dipole-dipole interaction mechanism in which the diffusion of the assemblies and molecules is taken into consideration. © 2009 The American Physical Society.
2009, Physical Review B - Condensed Matter and Materials Physics, 79 (7)[Refereed]
Scientific journal
The distribution of Ge composition and active B concentration in individual B-doped Si1-xGex alloy nanowires (SiGeNWs) grown by the vapor liquid solid (VLS) process is studied by micro Raman spectroscopy by shifting the measurement position from the catalyst side to the substrate side. The Raman data reveal that there is strong correlation between the Ge composition and the active B concentration within individual SiGeNWs. We show that B-doped SiGeNWs have a core - shell structure with a low-Ge composition and low-B concentration core grown by the VLS process covered with a high-Ge composition and high-B concentration shell grown by the conformal deposition. © 2009 American Chemical Society.
2009, Journal of Physical Chemistry C, 113 (14), 5467 - 5471[Refereed]
Scientific journal
Photoluminescence properties and optical absorption of the structures of silicon nanocrystals (nc-Si) in silicon dioxide matrix (SiO 2) are investigated in extended ranges of the excitation photon energy from 3 to 20 eV and the photon flux from 10 16 to 10 19 cm -2. The experimental data are explained by considering the quantum confinement in nc-Si, energy transfer (exciton diffusion in nc-Si ensembles) and light scattering in dielectrically inhomogeneous medium, as well as an influence of the electronic states in the SiO 2 matrix on the excitation/de- excitation processes in nc-Si. Copyright © 2009 American Scientific Publishers All rights reserved.
2009, Journal of Nanoelectronics and Optoelectronics, 4 (1), 147 - 151[Refereed]
Scientific journal
- Enhancement of upconversion luminescence from Er Doped Al
2 O3 films by a thin metal layerThe effect of a metal layer on upconversion luminescence of Er doped Al2O3 thin films is studied. Three visible luminescence peaks, which are assigned to 2H11/2 → 4I15/2, 4S3/2 → 4I15/2 and 4F9/2 → 4I15/2 transitions of Er3+, are observed by excitation with 978.5 nm light. When a Au or Ag layer is deposited on top of the samples, the upconversion luminescence intensity is strongly enhanced. Roughness at an Al2O3-metal interface is considered to play a significant role for the enhancement. From the comparison of the enhancement factors between the upconversion PL and downconversion PL excited by 488.0 nm light, the mechanism of the PL enhancement is discussed.
2009, ECS Transactions, 16 (31), 87 - 93[Refereed]
International conference proceedings
Er3+ and Ni2+ doped single-crystalline Al 18B4O33 nanorods were synthesized by a facile one-step toxic-free combustion method. The products were characterized by x-ray diffraction, transmission electron microscopy, selected area electron diffraction, and integrated and time-resolved photoluminescence (PL) measurements. The phase purity, morphology, and PL properties of Er3+ and Ni2+ doped Al18B4O33 nanorods can be readily controlled by tailoring the annealing temperature. The mechanism for the formation of Al18B4O33 nanorods with different aspect ratio is discussed. Er3+ doped Al18B 4O33 nanorods show strong PL centered at 1531 nm, while Ni2+ doped products show superwide PL with a full width at half maximum of up to 250 nm. These aluminum borate nanostructures are promising building blocks for optoelectronics nanodevices. © IOP Publishing Ltd.
2009, Nanotechnology, 20 (3), English[Refereed]
Scientific journal
Silicon nanowires (SiNWs) with a single-crystalline Si core and a thermally oxidized shell (core-shell SiNWs) were synthesized by gold-catalyzed chemical vapor deposition followed by rapid thermal oxidation. To synthesize high-quality core-shell SiNWs, the relationship between the growth parameters and the crystallinity was studied. Furthermore, the formation process of the oxide shell was analyzed in detail by transmission electron microscopy. Using SiNWs as channels, back gate-type field effect transistors (FETs) were fabricated on p-type silicon wafers. FETs with core-shell SiNWs channels exhibited smaller hysteresis in the drain current (Id) vs. gate voltage (VGS) characteristics and higher on/off drain current ratio (ION/IOFF) than those with bare SiNWs channels. © 2008 Elsevier B.V. All rights reserved.
2009, Thin Solid Films, 517 (16), 4520 - 4526, English[Refereed]
Scientific journal
Nonlinear optical properties of Si nanocrystals (Si-ncs) doped SiO2 prepared by a cosputtering method were studied by z -scan technique in a femtosecond regime at around 1.6 eV. The nonlinear refractive index (n2) and nonlinear absorption coefficient (Β) were strongly enhanced compared to those of bulk Si and found to be about ∼2× 10-13 cm2 /W and ∼0.8 cm/GW, respectively. In the photon energy region from 1.48 to 1.65 eV, the n2 and Β spectra followed the absorption spectra and no enhancement was observed in the band-edge photoluminescence region. In the diameter range of 2.7-5.4 nm, the size dependence of n2 coincided well with that calculated by a pseudopotential approach, suggesting that the discrete energy states of Si-ncs are responsible for the observed enhanced optical nonlinearity. © 2009 American Institute of Physics.
2009, Journal of Applied Physics, 105 (9), English[Refereed]
Scientific journal
Nonlinear optical properties of phosphorus (P) -doped silicon (Si) nanocrystals are studied by z-scan technique in femtosecond regime at around 1.6 eV. The nonlinear refractive index (n2) and nonlinear absorption coefficient (β) of Si-ncs are significantly enhanced by P-doping. The enhancement of n2 is accompanied by the increase of the linear absorption in the same energy region, suggesting that impurity-related energy states are responsible for the enhancement of the nonlinear optical response. © 2009 Optical Society of America.
2009, Optics Express, 17 (9), 7368 - 7376, English[Refereed]
Scientific journal
Nickel-doped forsterite (Ni2+:Mg2SiO4) nanocrystals have been synthesized by a facile molten-salt approach in the presence of NaCl and a surfactant (NP-7.5). The products were characterized by X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, selected area electron diffraction (SAED), and luminescence spectra measurements. The crystal size could be controlled by tailoring the synthesis parameters. TEM, high-resolution TEM, and SAED results revealed the single crystalline character of Mg2SiO4 nanoparticles. A possible model for the growth of Ni2+:Mg2SiO4 nanocrystals was postulated. The obtained Ni2+:Mg2SiO 4 nanocrystals show strong, super broad, near-infrared luminescence at room temperature. These doped Mg2SiO4 nanocrystals are promising gain mediums for super broadband optical amplification. © 2009 The American Ceramic Society.
2009, Journal of the American Ceramic Society, 92 (4), 962 - 966, English[Refereed]
Scientific journal
We have shown that efficient superbroadband near-IR luminescence can be realized in bismuth-doped high- silica nanocrystalline zeolites. The emission band covered the range of 930-1620 nm, with a maximum peak at 1146.3 nm, an FWHM of 152 nm, and a lifetime of over 300 μs under the excitation of a 488 nm laser line. The observed luminescence was attributed to subvalent Bi (Bi +) ions formed in the annealed zeolites. These Bi-doped nanozeolites may find applications as superbroadband near-IR nano-optical sources. © 2009 Optical Society of America.
2009, Optics Letters, 34 (8), 1219 - 1221, English[Refereed]
Scientific journal
Significantly enhanced superbroadband near infrared emission has been realized in bismuth/aluminum doped high-silica zeolite derived nanoparticles. The emission intensity can be easily tailored by the introduction of aluminum. The luminescence lifetime can reach up to 695 ìs. The results reveal that the existence of charge imbalance environment caused by [AlO4/2]- units in host materials is requisite to the formation of infrared-active Bi+. The finding presents a feasible route to design highefficient bismuth activated infrared luminescent nanoparticles. These bismuth doped nanoparticles may find applications as superbroadband near infrared nano optical sources. © 2009 Optical Society of America.
2009, Optics Express, 17 (8), 6239 - 6244, English[Refereed]
Scientific journal
We have shown that highly efficient and air-stable 1531 nm emission can be realized in erbium/bismuth codoped zeolites. The luminescence lifetime of Er3+ at 1531 nm can reach up to 4.2 ms. Bismuth compounds formed by high temperature annealing can act as blockages of selectively closing down the "in-out windows" of water molecules, i.e., Er3+ ions are sealed in a low-vibrational environment by bismuth agglomerates even when the samples contain a large amount of water. This finding may pave the way for the applications of active ions doped porous materials in infrared photonics. © 2009 American Institute of Physics.
2009, Applied Physics Letters, 94 (14), 141106, English[Refereed]
Scientific journal
Active B-concentration profiles of modulation doped p-type/intrinsic (p-i) and intrinsic/p-type (i-p) silicon nanowires (SiNWs) grown by a vapor-liquid-solid process were studied by analyzing Fano-type spectra in Raman spectroscopy. The analysis of Raman spectra of as-grown, annealed, and oxidized p-i and i-p SiNWs revealed that B atoms are mainly doped from the surface by conformal deposition of a heavily doped layer on the side wall of a SiNW. The surface doping results in strong gradient in B concentration along the axial and radial directions. © 2009 American Chemical Society.
2009, Journal of Physical Chemistry C, 113 (25), 10901 - 10906, English[Refereed]
Scientific journal
Photoluminescence spectra of a dye layer embedded in a metal-insulator-metal structure are investigated. Peculiar behaviors of the emission peaks observed can be well explained by a photoluminescence mechanism mediated by a symmetric surface plasmon polariton mode supported by the metal-insulator-metal structure. The enhancement in the photoluminescence intensities relative to those of a reference sample is clearly demonstrated. Theoretical analyses suggest that the enhancement in emission process is dominant. © 2009 Elsevier B.V. All rights reserved.
2009, Journal of Luminescence, 129 (12), 1997 - 1999, English[Refereed]
Scientific journal
The effect of metal nanostructures prepared by nanosphere lithography on photoluminescence (PL) properties of silicon nanocrystals (Si-ncs) is studied. By placing Ag nanotriangles or Au nanovoids on SiO2 films containing Si-ncs, the PL intensity is enhanced. For the sample having Ag nanotriangles, the largest PL enhancement is obtained when the excitation wavelength coincides with the absorption band of Ag nanotriangles. This suggests that the enhancement of the incident field by surface plasmon polariton (SPP) excitation is responsible for the PL enhancement. On the other hand, for the sample having Au nanovoids, the PL enhancement is mainly made by the enhancement of effective radiative decay rate of Si-ncs by efficient excitation and scattering of SPPs. © 2009 American Institute of Physics.
2009, Journal of Applied Physics, 106 (1), 013517 - 013517, English[Refereed]
Scientific journal
We performed reverse attenuated total reflection measurements on 50-nm-thick Ag thin films coated with oriented sexithiophene molecular layers. The dispersion curves obtained clearly demonstrate that the wavevectors of surface plasmon polaritons propagating parallel to the molecular orientation have larger magnitudes than those propagating perpendicular to the molecular orientation. The results provide us with an approach to generate anisotropic propagation of surface plasmon polaritons simply controlled by the molecular orientation of an overlayer. © 2009 American Institute of Physics.
2009, Applied Physics Letters, 95 (3), English[Refereed]
Scientific journal
Thin rhodamin B dye layers were deposited on gas-evaporated GaP particle layers and their fluorescence intensities were compared with those of the dye layers simultaneously deposited onto glass substrates. The intensities of the dye layers on the GaP particle layers were found to be greatly enhanced and the enhancement factor increased from ∼10 to ∼140 as the thickness of the dye layer is decreased from ∼50 to ∼1 nm. The present results clearly demonstrate that GaP particle layers, although they are not metallic and do not support surface plasmons, are good enhancer of fluorescence free from quenching. © 2009 Elsevier B.V. All rights reserved.
2009, Chemical Physics Letters, 480 (1-3), 100 - 104, English[Refereed]
Scientific journal
We report on highly efficient broadband near-infrared photoluminescence (PL) in Ni2+-doped glass ceramics (GCs) films fabricated by annealing Si/Ni2+-doped glass superlattices (SNGS). Over two orders of magnitude enhancement of PL can be achieved in comparison with that from the annealed glass film. The PL lifetime of the annealed SNGS is several milliseconds, which is much longer than those of bulk GCs. The strong PL enhancement results from the formation of high-quality cordierite nanocrystals because the Si layers act as Si source for the crystal growth. This technique can be extended to fabricate other types of high-quality GCs films. © 2009 Elsevier B.V. All rights reserved.
2009, Journal of Non-Crystalline Solids, 355 (48-49), 2425 - 2428, English[Refereed]
Scientific journal
Erbium silicate (Er 2SiO 5 and Er 4Si 3O 12) nanostructures were successfully synthesized by a facile molten-salt approach in the presence of NaCI and surfactant. The synthesized products were structurally and morphologically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM), whereas the luminescent properties were characterized by temperaturedependent luminescence measurements. The results revealed that the composition, crystalline phase, and yield of the final products can be readily controlled by choosing suitable surfactant and tailoring the molar ratio of reactants used for the reactions. Moreover, the single-crystalline nature of Er 2SiO 5 and of Er 4Si 3O 12 nanostructures results in sharp photoluminescence (PL) of Er 3+, and both nanostructures are immunized from temperature quenching of PL. We suggest that the nanostructures developed in the present work are promising building blocks for Si-based optoelectronics nanodevices. Copyright © 2009 American Scientific Publishers.
2009, Journal of Nanoscience and Nanotechnology, 9 (11), 6277 - 6282, English[Refereed]
Scientific journal
Er ions can be excited efficiently by energy transfer from Si nanocrystals. There are several different kinds of energy transfer processes depending on the distance between Si nanocrystals and Er ions. Among them, Forster-type dipole-dipole interaction is considered to have the longest interaction distance. In this work, we study how the long-distance interaction is modified when Er-Si-nanocrystals coupled system is placed near a metal layer. We show that the energy transfer rate is strongly modified by the metal layer and the rate oscillates depending,on the distance between the metal and the coupled system. From the quantitative analysis of the oscillation behavior, the energy transfer efficiency as well as the rate is estimated as a function of the energy transfer wavelength, and the evidence of resonant energy transfer is demonstrated. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
WILEY-V C H VERLAG GMBH, Jan. 2008, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 205 (1), 47 - 51, English[Refereed]
Scientific journal
Many properties of materials often undergo significant changes in a certain size range. For example, different forms of silicon nanocrystal assemblies have relatively high photoluminescence quantum yield due to morphological and quantum size effects. This chapter describes the main decay channel for photogenerated electron-hole pairs confined in silicon nanocrystals at high levels of optical excitation. We will argue that nonradiative Auger decay processes inherently limit quantum yield of photoluminescence of this system due to efficient competition with the radiation recombination. We further discuss implications of doping of silicon nanocrystals for their light emitting properties. © 2008 by Pan Stanford Publishing Pte. Ltd. All rights reserved.
2008, Silicon Nanophotonics: Basic Principles, Current Status and Perspectives, 397 - 424[Refereed]
Scientific journal
- Sensitized Generation of Singlet Oxygen by Allylamine-Terminated Hydrophilic Porous Si
We studied the sensitized generation of singlet oxygen by surface-modified hydrophilic porous Si. Porous Si consisting of a network of Si nanocrystals acts as an efficient photosensitizer for the generation of exited state molecular oxygen called singlet oxygen. Singlet oxygen is widely used in chemistry and biology. One of the possible applications of it is photodynamic therapy of cancer (PDT). However, as-prepared porous Si is hydrophobic and thus cannot be used as singlet oxygen photosensitizer in aqueous solution. Therefore, in this work, we modified the surface of porous Si by organic molecules (allylamine). We found that allylamine-terminated hydrophilic porous Si holds the photosensitization ability, although the efficiency of singlet oxygen generation is reduced by the modification.
MATERIALS RESEARCH SOCIETY JAPAN-MRS-J, 2008, Transactions of the Materials Research Society of Japan, Vol 33, No 1, 33 (1), 165 - 167, English[Refereed]
Scientific journal
The electronic excitation energy transfer between excitons in porous silicon and iodine molecules in an organic solution is studied. From the time-resolved photoluminescence the rate of the energy transfer is increased with approaching a wavelength region where the photoluminescence spectrum of porous silicon overlaps the absorption spectrum of iodine molecules, and with increasing the radiative recombination rate of porous silicon. We show that the dependence of the rate is well explained by Förster type dipole-dipole interaction mechanism in which the diffusion of the assemblies and molecules is taken into consideration. Furthermore, it is found that the efficiency of the energy transfer strongly depends on the emission wavelength at low iodine concentration. ©The Electrochemical Society.
2008, ECS Transactions, 16 (3), 267 - 276[Refereed]
International conference proceedings
The preceding miniaturization in microelectronics connected with the application of optical signals for information transfer demands siliconbased optical devices. Almost all the various photonic devices integrated on silicon wafer: e.g. silicon based optical waveguides, splitters, couplers, modulators, photonic crystals, detectors, etc. have already been demonstrated. These advances are based on welldeveloped silicon technology such as lithography, selective etching and silicon oxidation. This chapter describes another approach of engineering different silicon-based optical devices: it is based on indepth and in-plane nanostructuring of silicon wafers. In-depth variation of the refractive index is performed via porosification of silicon wafers aiming to achieve the desired spectral response of these devices while in-plane nanostructuring results in their polarization-dependent optical properties. © 2008 by Pan Stanford Publishing Pte. Ltd. All rights reserved.
Silicon Nanophotonics: Basic Principles, Current Status and Perspectives, 2008, Silicon Nanophotonics: Basic Principles, Current Status and Perspectives, 245 - 266[Refereed]
Scientific journal
- Sensitized Generation of Singlet Oxygen by Allylamine-Terminated Hydrophilic Porous Si
We studied the sensitized generation of singlet oxygen by surface-modified hydrophilic porous Si. Porous Si consisting of a network of Si nanocrystals acts as an efficient photosensitizer for the generation of exited state molecular oxygen called singlet oxygen. Singlet oxygen is widely used in chemistry and biology. One of the possible applications of it is photodynamic therapy of cancer (PDT). However, as-prepared porous Si is hydrophobic and thus cannot be used as singlet oxygen photosensitizer in aqueous solution. Therefore, in this work, we modified the surface of porous Si by organic molecules (allylamine). We found that allylamine-terminated hydrophilic porous Si holds the photosensitization ability, although the efficiency of singlet oxygen generation is reduced by the modification.
MATERIALS RESEARCH SOCIETY JAPAN-MRS-J, 2008, Transactions of the Materials Research Society of Japan, Vol 33, No 1, 33 (1), 165 - 167, English[Refereed]
Scientific journal
- Photoluminescence properties of Si nanocrystals near rough Au films
We studied metal-enhanced photoluminescence (PL) from Si nanocrystals (Si-ncs) placed near rough Au films. Au films with different degree of roughness were prepared by electroless Au plating. We found that the PL intensity and the decay rate increase as the roughness becomes large. The PL excitation spectra revealed that the PL enhancement is the largest when the excitation wavelength corresponds to that of the surface plasmon resonance of rough Au films. The result combined with the emission wavelength dependence of PL enhancement factors suggest that the PL enhancement is caused by the enhancement of an electric field of incident light due to the excitation of surface plasmons supported by the rough Au films and also the increase of radiative decay rate of Si-ncs.
MATERIALS RESEARCH SOCIETY JAPAN-MRS-J, 2008, Transactions of the Materials Research Society of Japan, Vol 33, No 1, 33 (1), 141 - 144, English[Refereed]
Scientific journal
Er ions can be excited efficiently by energy transfer from Si nanocrystals. There are several different kinds of energy transfer processes depending on the distance between Si nanocrystals and Er ions. Among them, Förster-type dipole-dipole interaction is considered to have the longest interaction distance. In this work, we study how the long-distance interaction is modified when Er-Si-nanocrystals coupled system is placed near a metal layer. We show that the energy transfer rate is strongly modified by the metal layer and the rate oscillates depending on the distance between the metal and the coupled system. From the quantitative analysis of the oscillation behavior, the energy transfer efficiency as well as the rate is estimated as a function of the energy transfer wavelength, and the evidence of resonant energy transfer is demonstrated. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.
2008, Physica Status Solidi (A) Applications and Materials Science, 205 (1), 47 - 51, English[Refereed]
Scientific journal
We designed and fabricated porous silicon-based broadband rugate filters by combining up to seven rugate structures. A near-infrared stop-band filter having a reflection band width of 1926 nm with no higher-order harmonics and very small sidelobes were realized. The suppression of higher-order harmonics and the reduction of sidelobes also allowed us to produce a high quality pass-band filter having three high transmittance regions consisting of broad stopbands. © The Electrochemical Society.
2008, ECS Transactions, 16 (3), 55 - 59, English[Refereed]
International conference proceedings
The significant fluorescence enhancement of immobilized CdTe nanocrystals through chemical surface modifications is described, enabling us to fabricate stable, highly luminescent thin films and patterns of nanocrystal mono- and mutilayers. © The Royal Society of Chemistry.
ROYAL SOC CHEMISTRY, 2008, Chemical Communications, No. 14, pp. 1641 - 1643 (14), 1641 - 1643, English[Refereed]
Scientific journal
On the surface of silicon nanowires (SiNWs) synthesized by gold (Au)-catalyzed chemical vapor deposition (CVD), Au particles 5-20 nm in diameter are formed if the growth conditions are within a specific range. We studied the mechanism of Au particle formation by growing SiNWs under different conditions, specifically by dynamically changing the growth parameters during the growth process. We show that insufficient supply of Si source to the Au-Si eutectic on top of the SiNWs enhances the migration of Au atoms on the surface of SiNWs in the form of Au-Si eutectic, which is precipitated on the surface as Au particles during cooling. We also show that using Au-Si eutectic on the surface of SiNWs as a catalyst enables one-step growth of branched SiNWs. © 2008 American Chemical Society.
2008, Nano Letters, 8 (1), 362 - 368, English[Refereed]
Scientific journal
Photoluminescence from a tris(8-hydroxyquinoline) aluminum (Alq 3) thin layer placed at various distances from a Ag thin film with the aid of a spacer layer was studied in a reverse attenuated total reflection geometry using a glass prism. Comparative studies of photoluminescence intensities and decay curves were performed for both the light emission into the free space and that into the prism. The prism-side emission, which arises via excitation and de-excitation of surface plasmon modes, showed spacer thickness dependence much different from that of the free-space emission. From a comparison with theoretical calculations, the optimum spacer thickness for the intensity of surface plasmon-mediated light emission was attributed to the optimum condition for surface plasmon excitation. The present experimental and theoretical results offer a guide to optimizing optical devices that utilize the surface plasmon-mediated light emission. © 2008 The Japan Society of Applied Physics.
2008, Japanese Journal of Applied Physics, 47 (2 PART 1), 1152 - 1157, English[Refereed]
Scientific journal
Strong enhancement of upconversion photoluminescence (PL) of Er3+ in the visible range was achieved by placing it near rough Ag island films. In order to understand the mechanism of the enhancement, PL was excited by 978 and 488 nm light and the enhancement factors were obtained in a wide spectral range (520 nm to 1.6 μm). The emission and excitation wavelength dependence of the enhancement factors revealed that both the incident electric fields and the radiative decay rate of Er3+ are enhanced due to the excitation of surface plasmons supported by Ag islands. It was found that the upconversion PL is more sensitive to the enhancement of the incident electric field than the downconversion PL because of the multiphoton absorption process. The present result indicates that the upconversion PL obtains more benefit from the metal-enhanced fluorescence technique than the downconversion PL. © 2008 American Institute of Physics.
2008, Applied Physics Letters, 92 (13), English[Refereed]
Scientific journal
We report resonant photon tunneling (RPT) through one-dimensional metamaterials consisting of alternating layers of metal and dielectric. RPT via a surface plasmon polariton state permits evanescent light waves with large wavenumbers to be conveyed through the meta-material. This is the mechanism for sub-wavelength imaging recently demonstrated with a super-lens. Furthermore, we find that the RPT peak is shifted from the reflectance dip with increasing the number of Al layers, indicating that the shift is caused by the losses in the RPT. © 2008 Optical Society of America.
OPTICAL SOC AMER, 2008, Optics Express, 16 (13), 9942 - 9950, English[Refereed]
Scientific journal
We present a high-resolution photoluminescence study of Er-doped SiO2 sensitized with Si nanocrystals (Si NCs). Emission bands originating from recombination of excitons confined in Si NCs, internal transitions within the 4f -electron core of Er3+ ions, and a band centered at λ≈1200 nm have been identified. Their kinetics were investigated in detail. Based on these measurements, we present a comprehensive model for energy-transfer mechanisms responsible for light generation in this system. A unique picture of energy flow between the two subsystems was developed, yielding truly microscopic information on the sensitization effect and its limitations. In particular, we show that most of the Er3+ ions available in the system are participating in the energy exchange. The long-standing problem of apparent loss of optical activity in the majority of Er dopants upon sensitization with Si NCs is clarified and assigned to the appearance of a very efficient energy exchange mechanism between Si NCs and Er3+ ions. Application potential of SiO2: Er, sensitized by Si NCs, was discussed in view of the newly acquired microscopic insight. © 2008 The American Physical Society.
2008, Physical Review B - Condensed Matter and Materials Physics, 78 (3), English[Refereed]
Scientific journal
P- and/or B-doped Si nanocrystals (Si-ncs) embedded in glass matrices were studied by electron spin resonance (ESR) spectroscopy to investigate the origin of strong room-temperature photoluminescence (PL) of n - and p -type impurities codoped Si-ncs below the band-gap energy of bulk Si crystals. It was shown that the intensity and width of the ESR signal depend strongly on impurity concentrations. A clear correlation was observed between the ESR signal width and the PL intensity. The observed correlation suggests that in addition to the geometrical confinement, P and B codoping further localize carriers in Si-ncs, and the strong localization results in the characteristic luminescence properties. © 2008 American Institute of Physics.
2008, Applied Physics Letters, 93 (2), English[Refereed]
Scientific journal
The distribution of electrically active B concentration in single SiNWs (nanowires) grown by a vapor-liquid-solid (VLS) process was studied by analyzing Fano resonance in Raman spectra. We found a gradient of active B concentration along the growth direction; the B concentration was the largest at the substrate side and the smallest at the catalyst side. The observed concentration gradient suggests the conformai growth of a high B concentration layer during a VLS process. To confirm this effect, we grew SiNWs with controlled impurity profiles, that is, p-type/intrinsic (p-i) and intrinsic/p-type (i-p) SiNWs, by controlling the supply of B source during SiNWs growth. We found that p-i SiNWs can be grown by just stopping the supply of B source in the middle of the growth, while i-p SiNWs were not realized; that is, the whole region of nominal "i-p" SiNWs was B-doped even if we started the supply of B source in the middle of the growth. These results confirm the above doping model. We also found that the distribution of active B concentration was significantly modified by high temperature annealing. By annealing at 1100 °C for 1 min, B concentration became almost uniform along 10 μm long SiNWs irrespective of initial B profiles. This suggests very efficient diffusion of B atoms in a defective high B concentration surface layer of SiNWs. © 2008 American Chemical Society.
2008, Nano Letters, 8 (9), 2620 - 2624, English[Refereed]
Scientific journal
Rugate filters made of anisotropically nanostructured birefringent silicon have been fabricated and studied by polarization-resolved transmission measurements. Electrochemical etching of a (110) oriented Si wafer results in porous silicon layers which exhibit a strong in-plane birefringence. We demonstrate that a sinusoidal refractive index variation of birefringent porous silicon combined with index-matching layers and apodization results in a dichroic rugate filter having a stop-band dependent on the polarization direction of the incident light without higher-order harmonics and sidelobes. We also demonstrate that the combination of different dichroic rugate filters allow us to realize filters with more complex properties in a single preparation step. © 2008 Optical Society of America.
2008, Optics Express, 16 (20), 15531 - 15539, English[Refereed]
Scientific journal
We designed and fabricated porous silicon-based broadband rugate filters by combining up to five rugate structures. A near-infrared stop-band filter having a reflection band width of 1356 nm with no higher-order harmonics and very small sidelobes were realized. The suppression of higher-order harmonics and the reduction of sidelobes also allowed us to produce a high quality pass-band filter exhibiting a high transmittance region sandwiched by two broad stop-bands. © 2008 Elsevier B.V. All rights reserved.
2008, Optical Materials, 31 (1), 102 - 105, English[Refereed]
Scientific journal
The initial stage of gold (Au)-catalyzed vapor-liquid-solid (VLS) growth of Si nanowires (SiNWs) was studied by transmission electron microscope (TEM) and atomic force microscope (AFM). Analysis and classification of the shape of SiNWs in TEM images revealed that there is strong correlation between the shape and crystallinity of Au catalysts and those of SiNWs, and the morphology of SiNWs is determined at a very early stage of the growth. The transition from initial horizontal growth of SiNWs on SiO2 substrates to vertical growth was studied by AFM, and it was demonstrated that SiNWs change growth direction abruptly by the formation of kinks. © 2008 American Chemical Society.
2008, Journal of Physical Chemistry C, 112 (44), 17121 - 17126, English[Refereed]
Scientific journal
The distribution of Ge composition in an individual Si1-x Gex alloy nanowire (SiGeNW) grown by the vapor liquid solid (VLS) process was studied by micro-Raman spectroscopy by changing the measurement position from the catalyst side to the substrate side. The Si-Si mode in Raman spectra were found to split into two peaks and the intensity ratio as well as the wavenumbers of the two peaks depended on the measurement position. The Raman data revealed that SiGeNWs have a core-shell structure with a low-Ge composition core grown by the VLS process covered with a high-Ge composition shell grown by the conformal deposition. © 2008 American Institute of Physics.
2008, Applied Physics Letters, 93 (20), English[Refereed]
Scientific journal
Large-scale synthesis of ytterbium silicate (Yb2SiO5) nanoparticles and nanorods has been realized by a facile molten-salt approach. The synthesized products were structurally and morphologically characterized by X-ray diffraction, transmission electron microscopy (TEM), and high-resolution TEM. Our results revealed that the morphologies of Yb2SiO5 products can be readily controlled by a simple variation of the reactants used for the molten-salt reaction. Single-crystalline Yb2SiO5 nanorods with a high yield can be obtained using NP-7.5 as a surfactant. The formation mechanism of Yb2SiO5 nanostructures was also discussed. The method presented here for the synthesis of Yb2SiO 5 nanostructures may pave the way for their application as environmental barrier coating materials. © 2008 The American Ceramic Society.
2008, Journal of the American Ceramic Society, 91 (12), 4158 - 4161, English[Refereed]
Scientific journal
We present a detailed study of the anisotropic optical properties of mesoporous silicon layers prepared from substrates having different doping levels under various preparation conditions. It is demonstrated that the morphology of the layers strongly depends on the preparation conditions. The experimental data are explained in the framework of an effective medium model which takes into account different morphologies of the layers. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
WILEY-V C H VERLAG GMBH, 2007, Physica Status Solidi C - Current Topics in Solid State Physics, Vol 4 No 6, 4 (6), 1996 - 2000, English[Refereed]
International conference proceedings
Temporal aspects of recombination and energy transfer processes in Er-doped SiO2 sensitized with Si nanocrystals (Si-nc's) were investigated by luminescence and excitation spectroscopy using time-correlated photon counting. This detection mode allows that emissions of very different intensities and dynamics may be investigated simultaneously, without loss of time resolution or amplitude deformation. In this way, components with decay constants ranging from nano- to milliseconds were identified in the luminescence bands of Si-nc's, Er3+ ions, and defects. We postulate to relate these to recombination processes originating from isolated Er3+ ions and Er3+ ions located inside or in direct vicinity of Si-nc's, with dynamics in the milli- and microsecond, and nanosecond range, respectively. In this way, a unique picture of the mutual relation between the two subsystems of Er3+ ions and Si-nc's, and truly microscopic information on the sensitization effect is obtained. Based on this new information, we conclude on a strong enhancement of non-radiative recombination of Er3+ upon sensitization with Si-nc's and put forward a complete description of Si-nc's as sensitizers of SiO2:Er system, where all the Er3+ ions available in the system are accounted for. © 2007 Elsevier B.V. All rights reserved.
2007, Physica E: Low-Dimensional Systems and Nanostructures, 38 (1-2), 144 - 147[Refereed]
Scientific journal
© 2007 by World Scientific Publishing Co. Pte. Ltd. All rights reserved. Photoluminescence (PL) properties of Er-doped structures of Si nanocrystals in SiO2 matrix are investigated at different temperatures and excitation intensities. Er-doped structures exhibit the PL line at 1.5 µm, which results from the radiative transitions in Er3+ ions excited by the energy transfer from Si nanocrystals. The PL yield and lifetime are found to be dependent on the nanocrystal size, temperature, and excitation intensity. The experimental results are explained by a strong coupling between excitons confined in Si nanocrystals and Er3+ ions in surrounding SiO2.
Physics, Chemistry and Application of Nanostructures: Reviews and Short Notes: Proceedings of the International Conference on Nanomeeting 2007 Minsk, Belarus, 22 - 25 May 2007, 2007, Physics, Chemistry and Application of Nanostructures: Reviews and Short Notes: Proceedings of the International Conference on Nanomeeting 2007 Minsk, Belarus, 22 - 25 May 2007, 148 - 156[Refereed]
Scientific journal
- AMER PHYSICAL SOC, 2007, Physical Review Letters, 99 (3), English
[Refereed]
Scientific journal
We present a detailed study of the anisotropic optical properties of mesoporous silicon layers prepared from substrates having different doping levels under various preparation conditions. It is demonstrated that the morphology of the layers strongly depends on the preparation conditions. The experimental data are explained in the framework of an effective medium model which takes into account different morphologies of the layers. © 2007 WILEY-VCH Verlag GmbH & Co. KGaA.
2007, Physica Status Solidi (C) Current Topics in Solid State Physics, 4 (6), 1996 - 2000, English[Refereed]
Scientific journal
- 2007, Transactions of the Materials Research Society of Japan, Vol. 32, No. 2, pp. 441-443, EnglishLuminescence Properties of Er and Si Nanoparticles Co-doped Aluminum Silicate Thin Films
[Refereed]
International conference proceedings
The properties of conduction electrons in P-doped Si nanocrystals embedded in insulating glass matrices have been studied by electron spin-resonance spectroscopy. For heavily P-doped samples, a broad conduction electron signal is observed at low temperatures. The width of the signal is found to be much broader than that of P-doped bulk Si crystals. The temperature dependence of the signal intensity obeys the Curie law even when the P concentration is very high. This suggests that in P-doped nanocrystals donor levels do not merge into the conduction band even at very high P concentration, and also provides evidence that Si nanocrystals smaller than a certain threshold size do not become metallic, at least when they are prepared under an equilibrium condition. © 2007 American Institute of Physics.
2007, Journal of Applied Physics, 101 (3), English[Refereed]
Scientific journal
The photoluminescence (PL) properties of Si nanocrystals embedded in In2O3/SiO2 thin films are studied. The PL properties strongly depend on In and excess Si concentrations. For the samples with an excess Si concentration larger than 3.4at.%, the PL intensity increases as In concentration increases up to 0.46 at.%, while the PL decay rate is nearly constant. This suggests that the number of Si nanocrystals contributing to the PL increases. On the other hand, when the excess Si concentration is low (1.4 at. %), the PL intensity monotonically decreases with increasing In concentration. The decrease in the PL intensity is accompanied by the increase in a decay rate, indicating that the nonradiative recombination process is introduced by In doping. © 2007 The Japan Society of Applied Physics.
2007, Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers, 46 (4 A), 1779 - 1782, English[Refereed]
Scientific journal
Hydrophilic porous Si is prepared by surface modification with polyethylene oxide (PEO) molecules. The surface modification is confirmed by infrared absorption spectroscopy and photoluminescence spectroscopy. The effect of surface modification on the efficiency of photosensitization of oxygen molecules, i.e., the efficiency of singlet oxygen generation, is studied. The PEO-terminated hydrophilic porous Si is shown to hold the photosensitization ability although the efficiency is reduced by the modification. © EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2007.
2007, European Physical Journal D, 43 (1-3), 193 - 196, English[Refereed]
Scientific journal
We have succeeded in forming C60 colloidal solution by laser irradiation of C60 powder suspended in a poor solvent. The formation of particles with an average diameter in the colloidal range was detected by transmission electron microscopy. A corresponding electron diffraction pattern revealed that the formed nanoparticles are fcc-structured C60 crystals. The mean size and size distribution of the formed C60 nanoparticles depended strongly on the fluence and wavelength of incident laser light. ©2007 The Japan Society of Applied Physics.
2007, Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers, 46 (7 A), 4338 - 4343, English[Refereed]
Scientific journal
The enhancement of photoluminescence (PL) is demonstrated from silicon nanocrystals (Si-ncs) by strong coupling of excitons to surface plasmon polaritons (SPPs) supported by a Au thin film. SPPs excited via excitons in Si-ncs were Bragg scattered to photons by one- or two-dimensional gratings, and strong and directional PL was obtained. From the angular dependence of PL spectra, dispersion relations of electromagnetic modes involved in the light emission process were obtained. The overall agreement between experimentally obtained and theoretically calculated dispersion relations confirmed that the strong and directional PL is mediated by SPPs. The PL decay rate of Si-ncs increased by placing a Au thin film on top and the wavelength dependence of the rate enhancement agreed well with that of the calculated SPP excitation rate. This suggests that the observed PL enhancement is due to efficient energy transfer from excitons to SPPs followed by efficient scattering of SPPs to photons, resulting in the enhancement of luminescence quantum efficiency. © 2007 American Institute of Physics.
2007, Journal of Applied Physics, 102 (2), English[Refereed]
Scientific journal
The effect of Au films with different thicknesses (20 and 100 nm) on the luminescence decay rate of Si nanocrystals was studied in a wide wavelength range. For the sample with the Au thickness of 100 nm, the luminescence decay rate oscillated depending on the distance between the Si nanocrystals and the Au film owing to the modification of the photonic mode density at the position of the Si nanocrystals. On the other hand, when the thickness of the Au film was 20 nm, the oscillation was not observed and a strong enhancement of the decay rate appeared in a small distance range. The degree of enhancement depended on the emission wavelength. These effects are considered to arise from a strong coupling between the electronic excitation of Si nanocrystals and the surface plasmon polariton modes supported by the rough Au surface. © 2007 The Japan Society of Applied Physics.
2007, Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers, 46 (10 A), 6498 - 6502, English[Refereed]
Scientific journal
We report complex dielectric function (ε) for yttrium-iron garnet thin films containing Au nanoparticles. Films are prepared using a co-sputtering method with post-annealing. Real and imaginary parts of e of the films are obtained using spectroscopic ellipsometry in a photon energy region from near-infrared to ultra-violet. An anomalous dispersion of Re[ε] in the visible region originating from localized surface plasmon of Au nanoparticles is clearly observed. The influence of e on the magnetooptical Kerr properties of the nanocomposite films is discussed. © 2007 The Japan Society of Applied Physics.
INST PURE APPLIED PHYSICS, 2007, Japanese Journal of Applied Physics, Part 2: Letters, 46 (41-44), L1032 - L1034, English[Refereed]
Scientific journal
The concentration of electrically active impurities in in situ boron (B)-doped silicon (Si) nanowires (SiNWs) synthesized by gold (Au)-catalyzed chemical vapor deposition (CVD) is studied by Raman spectroscopy. B-doped SiNWs exhibit an asymmetric Raman spectrum due to Fano resonance between discrete phonon Raman scattering and continuous electric Raman scattering caused by the excitation of holes in the valence band. To quantitatively evaluate the concentration of active B atoms from the asymmetric spectral shape, the spectra are fitted by a Fano resonance formula and asymmetry parameters are extracted. From the comparison of the asymmetry parameter with those obtained for reference samples, the concentration of active B atoms in SiNWs is estimated. The effects of thermal annealing in nitrogen and oxygen gases on the active B concentration are also studied. The annealing in nitrogen ambience for a short period significantly increases the concentration of active B atoms especially when the doping level is high, while longer period annealing decreases the active B concentration. The reduction of active B concentration is more significant when SiNWs are annealed in oxygen gas ambience. By combining Raman results with high-resolution transmission electron microscope observations, the growth mechanism of B-doped SiNWs is discussed. We show that the number of B atoms doped into SiNWs via Au catalysts is very limited and high B concentration layers are grown by conformal growth on the sidewall of SiNWs. © 2007 American Chemical Society.
2007, Journal of Physical Chemistry C, 111 (42), 15160 - 15165, English[Refereed]
Scientific journal
We observed azimuthal distributions of surface-plasmon-coupled emission from thin layers of randomly oriented and oriented sexithiophene molecules deposited on 50-nm -thick Ag films. For the randomly oriented layer, we observed a uniform and isotropic cone of emission, showing that the surface plasmons are excited isotropically in all directions on the Ag surface. The emission pattern for the oriented layer exhibited a much stronger intensity along the direction of molecular orientation, showing that surface plasmons propagating parallel to the molecular orientation are excited most effectively. These results demonstrate that surface-plasmon-coupled emission provides a new simple approach to the determination of molecular orientation in thin films. © 2007 American Institute of Physics.
2007, Applied Physics Letters, 91 (18), English[Refereed]
Scientific journal
Si1-x Gex alloy nanowires (SiGeNWs) were grown by Au-catalyzed chemical vapor deposition and studied by Raman spectroscopy, transmission electron microscopy (TEM), and energy-dispersive x-ray spectroscopy (EDS) in TEM (TEM-EDS). The relationship between the growth parameters and the structure of the SiGeNWs was clarified by systematically changing the growth conditions over a wide range. Raman and TEM-EDS results demonstrated that the SiGeNWs consist of a lower Ge composition core and a higher Ge composition shell epitaxially grown on the surface of the core. The effects of oxidation on the structure of the SiGeNWs were studied. It was found that oxidation leads to segregation of the Ge atoms at the interface between the SiGeNWs and SiO2, which in turn results in a large inhomogeneity in Ge composition. Oxidation at a very low rate in a diluted oxygen gas atmosphere is required to avoid the formation of Ge particles and minimize the inhomogeneity. © 2007 American Institute of Physics.
2007, Journal of Applied Physics, 102 (12), English[Refereed]
Scientific journal
- 31 Jan. 2006, 電子情報通信学会 信学技報 LQE2005-146, 2006 (1), 115 - 118, JapaneseApplication of Si・Er-codoped SiO_2 films to optical waveguide amplifiers
Scientific journal
- Magneto-optical Kerr effects of magnetic garnet thin films including plasmonic noble-metal nanoparticles
We report an experimental study on magneto-optical (MO) Kerr effects of yttrium iron garnet (YIG) films incorporating plasmonic Au nanoparticles. The results indicate a possible coupling between the MO Kerr effects and localized surface plasmons. © 2006 Optical Society of America.
2006, Optics InfoBase Conference Papers[Refereed]
International conference proceedings
Polyynes were synthesized by laser ablation of diamond particles with various sizes suspended in ethanol. Chain length distributions and total yields of polyynes produced were compared with those produced from graphitized diamond particles and graphite particles. The relative amounts of long polyynes such as C14H2 and C16H2 produced from diamond particles were found to be larger than those from graphitized diamond particles and graphite particles. From the change of the chain length distribution with the laser irradiation time, it is concluded that the long polyynes are produced directly from diamond particles at the initial stage of ablation. Furthermore, the total yield of polyynes was found to increase with the size of diamond particles and decrease as their graphitization proceeds. Possible mechanisms of these results are discussed. © 2005 Elsevier Ltd. All rights reserved.
2006, Carbon, 44 (3), 522 - 529, English[Refereed]
Scientific journal
The radiative recombination rate of excitons confined in Si nanocrystals was modified by placing a Au layer nearby. Oscillation of the rate was observed when the distance between the active layer and the Au layer was changed. By comparing the experimentally obtained oscillation behavior with a calculated one, the radiative and nonradiative recombination rates, and also the internal quantum efficiency of excitons in Si nanocrystals were estimated. The relation between the radiative rate and the luminescence wavelength was on a single curve for all the samples studied. On the other hand, the nonradiative rate depended strongly on samples. For the samples annealed at 1250°C, the estimated quantum efficiency was close to 100% at longer wavelength side of the luminescence bands, while the maximum quantum efficiency was 70% for the sample annealed at 1200°C. The present results provide evidence that in Si nanocrystal assemblies, the majority of nanocrystals in samples do not contribute to photoluminescence and a small part of nanocrystals luminesce with high quantum efficiencies, and thus the total quantum efficiency is mainly determined by the number ratio of bright and dark Si nanocrystals in the assembly. © 2006 The American Physical Society.
2006, Physical Review B - Condensed Matter and Materials Physics, 73 (24), English[Refereed]
Scientific journal
We investigate the time-resolved photoluminescence (PL) spectra of Si-nanocrystal (Si-nc)-doped SiO2 on Au thin films. It is shown that PL intensity within several tenth of μs after excitation is increased in the presence of Au films. The data suggest that the radiative recombination rate of excitons in Si-nc's is increased, and the degree of increase depends strongly on the emission photon energy. We show that the enhancement is caused by the modification of the local photonic mode density in the presence of Au thin films. © 2006 The Japan Society of Applied Physics.
2006, Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers, 45 (8 A), 6132 - 6136, English[Refereed]
Scientific journal
The rate of energy transfer from Si nanocrystals to Er ions was modified by placing a Au layer nearby. The distance between the active layer and the Au layer as well as the wavelength were changed systematically to quantitatively discuss how the energy transfer rate is modified by the photonic mode density. It was found that at particular combinations of the spacer thickness and the wavelength the energy transfer was strongly suppressed, while at other combinations it was enhanced. In order to understand the oscillation behavior of the energy transfer rate, a model fitting was performed. By assuming that the energy transfer rate is proportional to the square of the photonic mode density, the observed oscillation behavior could be well reproduced, and from the fitting the energy transfer rate could be estimated. The estimated rates of energy transfer to the I 11 2 4 and I 9 2 4 states of Er3+ were about 31 and 5.7 ks-1, respectively. © 2006 The American Physical Society.
2006, Physical Review B - Condensed Matter and Materials Physics, 74 (4), English[Refereed]
Scientific journal
A technique of surface-enhanced Raman scattering (SERS) with an Ag island film is applied to polyyne solutions produced by laser ablation of diamond particles suspended in ethanol. The technique is demonstrated to be very successful to observe Raman scattering from polyynes, which is not possible by a conventional method due to the strong luminescence. The observed Raman spectra exhibit a band around 2000 cm-1 with multiple peaks originating from conjugated triple bonds of polyynes. A change in the band shape observed by varying the polyyne concentration is thought to reflect the change in the length distribution of carbon linear chains. © 2005 Elsevier B.V. All rights reserved.
2006, Chemical Physics Letters, 420 (1-3), 166 - 170, English[Refereed]
Scientific journal
The effects of Au thin layers on luminescence properties of Er and Yb co-doped Al2 O3 films were studied. The 1.54 μm emission of Er3+ excited by the energy transfer from Yb3+ is found to be strongly enhanced by placing a Au layer on top of the films. Photoluminescence excitation spectra of the 1.54 μm PL of Er3+ and time transients of the 980 nm emission of Yb3+ revealed that PL enhancement arises from two different mechanisms. The first one is the enhancement of local electric fields accompanied by the excitation of surface plasmons of rough Au surfaces. The other one is the enhancement of energy transfer rate from Yb3+ to Er3+ caused by the modification of the local photonic mode density at the position of the Yb-Er coupled system. © 2006 American Institute of Physics.
2006, Applied Physics Letters, 88 (4), 1 - 3, English[Refereed]
Scientific journal
The luminescence properties of Si nanocrystals grown in In doped SiO 2 thin films are studied. It is shown that the luminescence properties depend strongly on the In concentration. At the In concentration of smaller than 0.46at.%, the photoluminescence (PL) intensity increases with increasing the In concentration, while the PL lifetime is nearly independent of the In concentration. This result indicates that the number of Si nanocrystals contributing to PL increases by In doping. When the In concentration exceeds 0.46 at. %, the PL intensity starts to decrease. The quenching is accompanied by the shortening of the lifetime, suggesting that nonradiative processes are introduced by In doping. However, even at a relatively high In concentration (∼3 at. %), the PL intensity is larger than that of Si nanocrystals in pure SiO2. © 2006 The Japan Society of Applied Physics.
2006, Japanese Journal of Applied Physics, Part 2: Letters, 45 (12-16), L450 - L452, English[Refereed]
Scientific journal
We report an experimental study on magneto-optical (MO) Kerr effects of yttrium-iron garnet (YIG) thin films incorporating Au nanoparticles. The polar MO Kerr spectra in the wavelength between 400 and 800nm show that, by incorporating the Au nanoparticles, Kerr rotation angles become negative values in the region, where the localized surface plasmon polariton (SPP) resonance of the Au nanoparticles is located. The anomalous Kerr rotation indicates a possible coupling between the MO Kerr effect of YIG and the SPP. A mechanism for the coupling is discussed. © 2006 The American Physical Society.
2006, Physical Review Letters, 96 (16), English[Refereed]
Scientific journal
We present a study of the photoluminescence (PL) of structures of Si nanocrystals (nc-Si) in erbium-doped amorphous silicon dioxide. It is shown that the energy of excitons confined in nc-Si of 2-5 nm sizes is efficiently transferred to Er3+ ions in surrounding SiO2 and a strong PL line at 1.5 μm appears. At high excitation intensity the population inversion of Er3+ ion states is achieved. These results demonstrate good perspectives of Er-doped nc-Si/SiO2 structures for possible applications in Si-based optical amplifiers and lasers. © 2006 Elsevier B.V. All rights reserved.
2006, Journal of Non-Crystalline Solids, 352 (9-20 SPEC. ISS.), 1192 - 1195, English[Refereed]
Scientific journal
Surface plasmon polaritons (SPPs) of a metal film can efficiently be excited when a light emitter is placed nearby. The excited SPPs are converted to photons by compensating for the momentum mismatch. The authors study SPP-mediated emission from excitons in Si nanocrystals (Si-nc's) by placing an organic grating on a thin Au film placed near Si-nc's. The dispersion relation is obtained from angle-resolved photoluminescence measurements, and all the observed modes are well explained by model calculation. The results indicate that excitons in Si-nc's can efficiently excite SPPs in thin metal films and directed photoluminescence can be realized. © 2006 American Institute of Physics.
2006, Applied Physics Letters, 89 (10), 101907 - 101907, English[Refereed]
Scientific journal
We report on an observation of a fast 1.5μm photoluminescence band from Er3+ ions embedded in an SiO2 matrix doped with Si nanocrystals, which appears and decays within the first microsecond after the laser excitation pulse. We argue that the fast excitation and quenching are facilitated by Auger processes related to transitions of confined electrons or holes between the space-quantized levels of Si nanocrystals dispersed in SiO2. We show that a great part-about 50%-of all Er dopants is involved in these fast processes and contributes to the submicrosecond emission. © 2006 The American Physical Society.
2006, Physical Review Letters, 97 (20), English[Refereed]
Scientific journal
Solutions of hydrogen-capped polyynes were prepared by laser ablation of graphite powder in n-hexane and subjected to size separation by high-performance liquid chromatography. Solutions of size-selected polyynes CnH2 (n = 8-16) were investigated by normal Raman (NR) and surface-enhanced Raman scattering (SERS) spectroscopy. A main band appearing in the 2000-2200 cm-1 region of the NR spectra showed a systematic downward shift as the chain length increased. The observed NR bands were assigned to Raman-active CC stretching vibrational modes by comparison with calculations based on density functional theory. Raman bands observed in SERS spectra were very broad and located at frequencies lower than the NR bands. A systematic band shift with increasing chain length was also observed for one of the bands. This band was thus assigned to a counterpart of the strong band in the NR spectra. These results made it possible to assign the origins of previously reported SERS bands of mixed polyyne solutions. © 2006 Elsevier Ltd. All rights reserved.
2006, Carbon, 44 (15), 3168 - 3176, English[Refereed]
Scientific journal
Generation of singlet oxygen due to energy transfer from photoexcited silicon nanocrystals in D2 O is demonstrated. It is shown that the singlet oxygen generation efficiency, i.e., the intensity of near-infrared emission from singlet oxygen gradually decreases when Si nanocrystals are continuously irradiated in O2 -saturated D2 O. The mechanism of the photodegradation of the photosensitizing efficiency is studied using photoluminescence and infrared absorption techniques. Experimental results suggest that the interaction of photogenerated singlet oxygen with the hydrogen-terminated surface of silicon nanocrystals results in photo-oxidation of silicon nanocrystals, and the surface oxides reduce the photosensitizing efficiency. It is also demonstrated that photo-oxidation of porous silicon in O2 -saturated water results in a strong enhancement of the photoluminescence quantum yield of porous Si. © 2006 American Institute of Physics.
2006, Journal of Applied Physics, 100 (12), English[Refereed]
Scientific journal
Anisotropic nanostructuring of bulk silicon (Si) wafers leads to a significant in-plane optical anisotropy of single porous silicon (PSi) layers. Additionally a variation of the etching current in time allows a controlled modification of the porosity along the growth direction and therefore a three-dimensional variation of the refractive index (in-plane and in-depth). This technique can be important for photonic applications since it is the basis of a development of a variety of novel, polarization-sensitive, silicon-based optical devices: retarders, dichroic Bragg reflectors, dichroic microcavities and planar Si-based polarizers. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
WILEY-V C H VERLAG GMBH, Jun. 2005, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 202 (8), 1432 - 1436, English[Refereed]
Scientific journal
Singlet oxygen formation by porous Si in solution has been demonstrated. It has been shown that the absorption band of 1,3-diphenylisobenzofuran (DPBF) in benzene becomes smaller, i.e., DPBF is degraded, by irradiating green or red light if the powder of fresh porous Si is dispersed in the solution. The effect was drastically suppressed by the formation of a monolayer of backbonded oxide at the surface of nanocrystals. The degradation was accelerated when the solution was bubbled with oxygen gas. These results indicate that electronic excitation of Si nanocrystals is transferred to molecular oxygen dissolved in solution, resulting in the formation of singlet oxygen. Generated singlet oxygen reacts with DPBF, forming endoperoxides, which in turn decompose to yield irreversible products. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
WILEY-V C H VERLAG GMBH, Jun. 2005, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 202 (8), 1385 - 1389, English[Refereed]
Scientific journal
- May 2005, Physical Review B, 71・115440・1-7 (11), English
[Refereed]
Scientific journal
- Photoluminescence fatigue effect in luminescent porous silicon induced by photosensitized molecular oxygen
We report on the mechanism of photodegradation of hydrogenated porous silicon luminescence in ambients containing molecular oxygen. Energy transfer from excitons confined in silicon nanocrystals assembling porous silicon layers to molecular oxygen results in the generation of highly chemically reactive singlet oxygen molecules. Their subsequent interaction with the hydrogenated surface of silicon nanocrystals results in its photooxidation and creation of additional nonradiative defects, i.e. the luminescence fatique effect. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
WILEY-V C H VERLAG GMBH, 2005, PHYSICA STATUS SOLIDI C - CONFERENCES AND CRITICAL REVIEWS, VOL 2, NO 9, 2 (9), 3188 - 3192, English[Refereed]
International conference proceedings
The mechanism of energy transfer from silicon nanocrystals (Si-nc's) to erbium (Er) ions is studied by analyzing time transient of Er photoluminescence at 1.54 μm. It is shown that two different energy transfer mechanisms, i.e., fast and slow, exist in SiO2 films containing Si-nc's and Er ions, and that the ratio of slow to fast processes depends on size of Si-nc's and Er concentration. A quantitative analysis reveals that Er ions located within about 1.5 nm from the surface of Si-nc's are excited by the fast process, and those located within about 2.5 nm by the slow process if no Er ions exist within 1.5 nm from the surface. Er ions staying outside these regions cannot be sensitized by Si-nc's. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2005.
2005, European Physical Journal D, 34 (1-3), 161 - 163[Refereed]
Scientific journal
We synthesized polyynes by laser ablation of diamond nanoparticles (about 5 nm in diameter) and graphite particles with two different sizes (about 5 nm and 10 μm) suspended in liquid ethanol. It was found that the ablation of diamond nanoparticles results in larger amounts of long polyynes compared to the ablation of graphite particles. It was also found that the chain length distribution of polyynes produced from diamond nanoparticles is dependent on the laser irradiation time and the fraction of long polyynes is higher when the irradiation time is shorter. These results allow us to conclude that the direct evaporation of carbon atoms from pristine diamond nanoparticles at the initial stage of laser irradiation results in the larger amounts of long polyynes. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2005.
2005, European Physical Journal D, 34 (1-3), 223 - 225[Refereed]
Scientific journal
We report on a medium exhibiting extremely efficient light scattering properties: a liquid network formed in a porous matrix. Liquid fragments confined in the solid matrix result in a random fluctuation of the dielectric function and act as scattering objects for photons. The optical scattering efficiency is defined by the filling factor of the liquid in the pores and its dielectric constant. The spectral dependence of the scattering length of photons indicates that the phenomenon is governed by a Mie-type scattering mechanism. The degree of the dielectric disorder of the medium, i.e. the level of opacity is tunable by the ambient vapor pressure of the dielectric substance. In the strongest scattering regime the scattering length of photons is found to be in the micrometer range. By incorporation of dye molecules in the voids of the porous layer a system exhibiting optical gain is realized. In the multiple scattering regime the optical path of diffusively propagating photons is enhanced and light amplification through stimulated emission occurs: a strong intensity enhancement of the dye emission accompanied by significant spectral narrowing is observed above the excitation threshold for a layer being in the opalescence state.© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
2005, Physica Status Solidi C: Conferences, 2 (9), 3268 - 3272[Refereed]
International conference proceedings
The energy transfer from Si nanocrystals (Si-nc's) to Er ions was studied spectroscopically. At low temperatures, inhomogeneously broadened photoluminescence bands of Si-nc's were partially quenched and some dips were observed. A comparison of the quenched spectra with a photoluminescence excitation spectrum revealed that the dips are due to the resonant energy transfer from excitons in Si-nc's to Er ions. For the energy transfer to the I 11 2 4 state of Er ions, two dips, one very clear and the other indistinctive, were observed, while to the I 9 2 4 state, two dips with comparable depth were observed. Modification of the band structure of Si-nc's by the quantum size effects is responsible for the different dip structures, depending on to which states the energy transfer is made. © 2005 The American Physical Society.
2005, Physical Review B - Condensed Matter and Materials Physics, 71 (19)[Refereed]
Scientific journal
Singlet oxygen formation by porous Si in solution has been demonstrated. It has been shown that the absorption band of 1,3-diphenylisobenzofuran (DPBF) in benzene becomes smaller, i.e., DPBF is degraded, by irradiating green or red light if the powder of fresh porous Si is dispersed in the solution. The effect was drastically suppressed by the formation of a monolayer of backbonded oxide at the surface of nanocrystals. The degradation was accelerated when the solution was bubbled with oxygen gas. These results indicate that electronic excitation of Si nanocrystals is transferred to molecular oxygen dissolved in solution, resulting in the formation of singlet oxygen. Generated singlet oxygen reacts with DPBF, forming endoperoxides, which in turn decompose to yield irreversible products. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
2005, Physica Status Solidi (A) Applications and Materials Science, 202 (8), 1385 - 1389[Refereed]
Scientific journal
Anisotropic nanostructuring of bulk silicon (Si) wafers leads to a significant in-plane optical anisotropy of single porous silicon (PSi) layers. Additionally a variation of the etching current in time allows a controlled modification of the porosity along the growth direction and therefore a three-dimensional variation of the refractive index (in-plane and in-depth). This technique can be important for photonic applications since it is the basis of a development of a variety of novel, polarization-sensitive, silicon-based optical devices: retarders, dichroic Bragg reflectors, dichroic microcavities and planar Si-based polarizers. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
2005, Physica Status Solidi (A) Applications and Materials Science, 202 (8), 1432 - 1436[Refereed]
Scientific journal
© 2005 by World Scientific Publishing Co. Pte. Ltd. All rights reserved. Structures of silicon nanocrystals in erbium-doped silicon dioxide (nc-Si/SiO2:Er) exhibit efficient photoluminescence of Er,+ ions at 1.5 µm. The population inversion of Er,+ energy states can be achieved under strong optical pumping because of the energy transfer from the excitons in Si nanocrystals to the ions. The results obtained are discussed in view of possible applications of nc-Si/SiO2:Er structures in optical amplifiers and lasers compatible with Si-based technology.
Physics, Chemistry, and Application of Nanostructures: Reviews and Short Notes to Nanomeeting 2005: Minsk, Belarus, 24-27 May 2005, 2005, Physics, Chemistry, and Application of Nanostructures: Reviews and Short Notes to Nanomeeting 2005: Minsk, Belarus, 24-27 May 2005, 128 - 131[Refereed]
Scientific journal
The luminescence properties of Si nanocrystals embedded in SiO xNy thin films were studied. At relatively low N concentrations (≈1.0 at. %) an increase in the photoluminescence (PL) intensity and a lengthening of the PL lifetime were observed, suggesting that non-radiative recombination centers on the surface of Si nanocrystals are terminated by N atoms. The increase was accompanied by the redshift of the luminescence band. The redshift indicates that the effect is more efficient for larger Si nanocrystals. At N concentration higher than 1.4at. %, the PL intensity was smaller than that of the sample without N doping. PL quenching in a high-N-concentration range is due probably to the introduction of new nonradiative recombination centers generated by N induced stress. © 2005 The Japan Society of Applied Physics.
2005, Japanese Journal of Applied Physics Part 2-Letters & Express Letters, 44 (50-52), L1547 - L1549[Refereed]
Scientific journal
We report on the mechanism of photodegradation of hydrogenated porous silicon luminescence in ambients containing molecular oxygen. Energy transfer from excitons confined in silicon nanocrystals assembling porous silicon layers to molecular oxygen results in the generation of highly chemically reactive singlet oxygen molecules. Their subsequent interaction with the hydrogenated surface of silicon nanocrystals results in its photooxidation and creation of additional nonradiative defects, i.e. the luminescence fatique effect. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
2005, Physica Status Solidi C - Conferences and Critical Reviews, Vol 2, No 9, 2 (9), 3188 - 3192[Refereed]
Scientific journal
Photoluminescence (PL) properties of Er and Si nanocrystals co-doped S1O2 films are studied in a wide Er concentration range. In the Er concentration range of less than 3 at%, Er3+ was excited by the energy transfer from Si nanocrystals. Above this concentration, Si nanocrystals and Er do not exist independently but amorphous or crystallin alloys of Si-Er-O are formed. In this region Er can be excited only by directly absorbed excitation light. The highest PL intensity is observed in the Er concentration range where an amorphous alloy of Si-Er-O is formed. © World Scientific Publishing Company.
2005, International Journal of Modern Physics B, 19 (15-17), 2598 - 2603[Refereed]
Scientific journal
Photoluminescence properties of Er-doped nanocrystalline Si/ SiO 2 structures have been investigated under strong optical excitation. The energy of optical excitation of Si nanocrystals was shown to be almost completely transferred to Er3+ ions in surrounding SiO2. It was found that at high pump intensity the energy transfer process competes successfully with nonradiative Auger-recombination in Si nanocrystals. At high excitation level the population inversion of Er3+ ions was achieved and a decrease of the decay time of the photoluminescence at 1.5 μm was observed. Possible mechanisms of the shortening of the Er3+ ion lifetime are discussed.
2005, Advanced Laser Technologies 2004, 5850, 20 - 24[Refereed]
International conference proceedings
The interaction between Er 3+ and shallow impurities in Si nanocrystals (nc-Si) is studied for SiO 2 films containing Er and nc-Si (Er:nc-Si:SiO 2). The luminescence property of Er 3+ is strongly modified by shallow impurities in nc-Si. The formation of excess carriers in nc-Si by P or B doping results in the quenching of infrared photoluminescence (PL) of Er 3+ and the shortening of the lifetime. When P and B are doped simultaneously and carriers are compensated, the intensity and the lifetime are recovered. It is shown that the mechanism of the interaction is Auger de-excitation of excited Er 3+ with the interaction of electrons or holes in nc-Si. The estimated Auger coefficient is found to be two orders of magnitude smaller than that of Er doped bulk Si at low temperatures where carriers are bound to donor or acceptor ions, and four orders of magnitude smaller than that at room temperature. This small Auger coefficient makes nc-Si immune from the impurity Auger de-excitation process compared to Er doped bulk Si and is considered to be responsible for temperature independent efficient PL of Er:nc-Si:SiO 2 systems. ©2005 The American Physical Society.
2005, Physical Review B - Condensed Matter and Materials Physics, 71 (11), 115440 - 115440[Refereed]
Scientific journal
We present a detailed study of the anisotropic optical properties of mesoporous silicon layers prepared from substrates having different doping levels under various preparation conditions. We demonstrate that the morphology of the layers strongly depends on the preparation conditions. It correlates with measured optical anisotropy values and defines the directions of the optical axes. The experimental data are explained in the framework of an effective medium model which takes into account the different morphologies of the layers. Modifications of the optical anisotropy of the layers in a controlled manner by filling the pores with dielectric substances and by oxidation of the structure confirm that form birefringence is the origin of the optical anisotropy. © 2005 The American Physical Society.
2005, Physical Review B - Condensed Matter and Materials Physics, 71 (19), English[Refereed]
Scientific journal
A 1.54-μm emission from erbium-doped sol-gel Si O2 was strongly enhanced by doping Au nanoparticles. The enhancement factor depended on Au concentration and was the largest at the concentration of 1.0 mol %. The photoluminescence enhancement was accompanied by the lengthening of the lifetime, suggesting that the enhancement is caused by the decrease of hydroxyl groups. In addition, enhancement due to strong fields induced by localized surface plasmon of Au nanoparticles was observed. © 2005 American Institute of Physics.
2005, Journal of Applied Physics, 98 (2), English[Refereed]
Scientific journal
The formation of singlet oxygen due to the energy transfer from excitons confined in silicon nanocrystals to oxygen molecules is studied using time-resolved photoluminescence spectroscopy. The process of the excitation of oxygen molecules from the ground triplet state to the second excited singlet state is studied at low temperatures, where oxygen molecules are physisorbed on the surface of silicon nanocrystals and at room temperature in gaseous oxygen ambient and in oxygen-saturated water. The low temperature measurements reveal that the energy transfer time is the shortest for the resonant energy transfer. The involvement of one energy-conserving transversal optical phonon results in about 40% increase of the energy transfer time. The excitation rate of oxygen dimers is found to be similar to that measured for oxygen molecules. At room temperature, the time of the energy transfer to oxygen molecules is about 17μs. The photosensitizing efficiency of silicon nanocrystals at room temperature is found to be as high as 80% for gaseous oxygen ambient and for oxygen-saturated water. © 2005 The American Physical Society.
2005, Physical Review B - Condensed Matter and Materials Physics, 72 (16), English[Refereed]
Scientific journal
Molecular oxygen plays an important role in many of the chemical reactions involved in the synthesis of biological life. In this review, we explore the interaction between O2 and silicon nanocrystals, which can be employed in the photosynthesis of singlet oxygen. We demonstrate that nanoscale Si has entirely new properties owing to morphological and quantum size effects, i.e., large accessible surface areas and excitons of variable energies and with well-defined spin structures. These features result in new emerging functionality for nanoscale silicon: it is a very efficient spin-flip activator of O2, and therefore, a chemically and biologically active material. This whole effect is based on energy transfer from long-lived electronic excitations confined in Si nanocrystals to surrounding O2 via the exchange of single electrons of opposite spin, thus enabling the spin-flip activation of O2. Further, we discuss the implications of these findings for physics, chemistry, biology, and medicine. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
2005, Advanced Materials, 17 (21), 2531 - 2544, English[Refereed]
Scientific journal
Photoluminescence (PL) properties of B and P codoped and compensated Si nanocrystals were studied. The compensation of carriers in nanocrystals was confirmed by the annihilation of confined-carrier optical absorption in the infrared region. In the PL spectra obtained under the resonant excitation condition, the codoped samples did not exhibit structures related to momentum-conserving phonons, which were clearly observed for pure Si nanocrystals. The result strongly suggests that in impurity codoped Si nanocrystals, nonphonon quasidirect optical transition is the dominant recombination path for electron-hole pairs, and thus impurity codoping is a possible approach to further improving PL efficiency of Si nanocrystals. © 2005 American Institute of Physics.
2005, Applied Physics Letters, 87 (21), 211919 - 211919, English[Refereed]
Scientific journal
The luminescence properties of Si nanocrystals embedded in SiOxNy thin films were studied. At relatively low N concentrations (approximate to 1.0 at. %) an increase in the photoluminescence (PL) intensity and a lengthening of the PL lifetime were observed, suggesting that non-radiative recombination centers on the surface of Si nanocrystals are terminated by N atoms. The increase was accompanied by the redshift of the luminescence band. The redshift indicates that the effect is more efficient for larger Si nanocrystals. At N concentration higher than 1.4 at. %, the PL intensity was smaller than that of the sample without N doping. PL quenching in a high-N-concentration range is due probably to the introduction of new nonradiative recombination centers generated by N induced stress.
INST PURE APPLIED PHYSICS, 2005, Japanese Journal of Applied Physics, Part 2: Letters, 44 (50-52), L1547 - L1549, English[Refereed]
Scientific journal
The effects of a Au thin layer on the rate of energy transfer from Si nanocrystals (Si-nc's) to Er3+ were studied. The energy transfer rate was found to oscillate with increasing the separation between the active layer and the Au thin film. The period of the oscillation agreed well with that of the calculated radiative decay rates of Si-nc's at the energy transfer wavelength. The present results provide evidence that the rate of energy transfer from Si-nc's to Er3+ is proportional to the photonic mode density at the energy transfer wavelength and can be controlled by controlling the photonic environment. © 2005 The American Physical Society.
2005, Physical Review B - Condensed Matter and Materials Physics, 72 (23), English[Refereed]
Scientific journal
Photoluminescence (PL) from singlet oxygen generated by energy transfer from porous Si is observed at room temperature in an organic solvent. The evidence of the indirect excitation by energy transfer is obtained from PL excitation spectroscopy. The excitation spectrum indicates that by using porous Si as a photosensitizer, light of the entire visible range can be utilized for singlet oxygen generation at room temperature.
2004, Physical Review B - Condensed Matter and Materials Physics, 70 (8)[Refereed]
Scientific journal
- Optical devices based on anisotropically nanostructured silicon
Anisotropic nanostructuring of bulk silicon (Si) leads to a significant optical anisotropy of single porous silicon (PSi) layers. A variation of the etching current in time allows a controlled modification of the porosity along the growth direction and therefore a three-dimensional variation of the refractive index (in plane an in depth). This technique can be important for photonic applications since it is the basis of a development of a variety of novel, polarization sensitive, silicon-based optical devices: retarders, dichroic Bragg Reflectors, dichroic microcavities and Si based polarizers.
MATERIALS RESEARCH SOCIETY, 2004, Engineered Porosity For Microphotonics and Plasmonics, 797, 21 - 26, English[Refereed]
International conference proceedings
By analyzing the time transient of PL from Er3+ doped into SiO2 films containing nc-Si, two energy transfer processes were found to coexist in each sample. The ratio of the two processes exhibited a clear dependence on the PL peak energy of Si nanocrystals, indicating that the ratio depends on the size of the nc-Si sensitizer. The results implied that, from the point of view of application as an amplifier and a light-emitting device, perfect nc-Si that possess the indirect band gap character of bulk Si crystals was not suitable.
2004, Journal of Applied Physics, 95 (1), 272 - 280, English[Refereed]
Scientific journal
Silicon-based thin-film polarizers operating in the visible and near-infraed spectral range are fabricated by electrochemical etching of bulk silicon wafers. Anisotropically etched (110) porous silicon layers exhibit a strong in-plane anisotropy of the refractive index. Stackes of alternating layers with different mean refractive indices and thicknesses act as dichroic Bragg ref lectors or microcavities, respectively. Both structures have two distinct ref lection and transmission bands depending on the polarization of the incident linearly polarized light. Planar polarizers are realized through the combination, in one structure, of a dichroic ref lector with either a second ref lector or a microcavity with different spectral responses. © 2004 Optical Society of America.
2004, Optics Letters, 29 (2), 195 - 197, English[Refereed]
Scientific journal
We report on a strong intrinsic optical anisotropy of silicon induced by its dielectric nanopatterning. As a result, an in-plane birefringence for nanostructured (110) Si surfaces is found to be 105 times stronger than that observed in bulk silicon crystals. A difference in the main values of the anisotropic refractive index exceeds that one of any natural birefringent crystals. The anisotropy parameters are found to be strongly dependent on the typical size of the silicon nanowires assembling the layers. The value of birefringence is dependent also on the dielectric surrounding of silicon nanoparticles assembling these layers. We show that stacks of layers having alternative refractive indices act as a distributed Bragg reflectors or optical microcavities. Dichroic reflection/transmission behavior of these structures sensitive to the polarization of the incident linearly polarized light is demonstrated. These findings open the possibility of an application of optical devices based on birefringent silicon layers in a wide spectral range.
2003, Proceedings of SPIE - The International Society for Optical Engineering, 5065, 12 - 22[Refereed]
International conference proceedings
- Optical devices based on anisotropically nanostructured silicon
Anisotropic nanostructuring of bulk silicon (Si) leads to a significant optical anisotropy of single porous silicon (PSi) layers. A variation of the etching current in time allows a controlled modification of the porosity along the growth direction and therefore a three-dimensional variation of the refractive index (in plane an in depth). This technique can be important for photonic applications since it is the basis of a development of a variety of novel, polarization sensitive, silicon-based optical devices: retarders, dichroic Bragg Reflectors, dichroic microcavities and Si based polarizers.
2003, Materials Research Society Symposium - Proceedings, 797, 21 - 26[Refereed]
International conference proceedings
- Microscopic study of thin films of Ni-filled carbon nanocapsules
The work reports on Scanning Probe Microscopy (SPM) of electrical and magnetic properties of thin (∼30 nm in thickness) Ni-C nanocomposite films. The films were prepared on Si substrates by cosputtering Ni and graphite, and subsequent thermal annealing in vacuum at 400°C that led to a self-assembly of Ni-filled carbon nanocapsules (∼ 5 nm in size) uniformly dispersed in the film. The SPM measurements were carried out in a combined Scanning Tunneling Microscopy/Atomic Force Microscopy (STM/AFM) device Solver P47. Spreading resistance imaging with STM revealed a periodical structure in which the cell consisted of a low conducting central part and a periphery region 0.5-1 nm in size, with high conductivity inclusions. The cell was found to be about 5 nm in diameter that allowed us to associate this object with the carbon nanocapsule. In magnetic force microscopy (MFM) measurements, a phase shift of the Co-coated cantilever oscillations was registered during scanning. It was established that the phase image had a spotted structure with the spot size of 0.2-0.5 μm. The phase signal inside the spot was found to be irregular. Such results were obtained irrespectively of the magnetization history, i.e., whether the sample was magnetized normal or parallel to the surface, or was demagnetized. The influence of electrodynamic forces on the accuracy of MFM measurements was analyzed.
2003, Physics of Low-Dimensional Structures, 3-4, 283 - 288[Refereed]
Scientific journal
- Energy exchange between optically excited silicon nanocrystals and molecular oxygen
We report on the photosensitizing properties of optically excited Silicon (Si) nanocrystal assemblies that are employed for an efficient generation of singlet oxygen. Spin triplet state excitons confined in Si nanocrystals transfer their energy to molecular oxygen (MO) adsorbed on the nanocrystal surface. This process results in a strong suppression of the photoluminescence (PL) from the Si nanocrystal assembly and in the excitation of MO from the triplet ground state to singlet excited states. The high efficiency of the energy transfer if favored by a broad energy spectrum of photoexcited excitons, a long triplet exciton lifetime and a highly developed surface area of the nanocrystal assembly. Due to the specifics of the coupled system Si nanocrystal oxygen molecule all relevant physical parameters describing the photosensitization process are accessible experimentally. This includes the role of resonant and phonon-assisted energy transfer, the dynamics of energy transfer, and its mechanism.
2003, Materials Research Society Symposium - Proceedings, 789, 17 - 22[Refereed]
International conference proceedings
We report on a spectroscopic study of electronic energy transfer from excitons confined in silicon nanocrystals to triplet ground-state oxygen molecules, being either physisorbed on the nanocrystal surface or present in the gas phase. The broad photoluminescence spectrum of the nanocrystal assembly probes the transfer of excitation and verifies that nonresonant energy transfer proceeds via multiphonon emission. At low temperatures a small spatial separation of the interacting species and a long lifetime of triplet-state excitons provide the strongest coupling. The energy-transfer time to the first and second excited states of molecular oxygen is in the range of 100 μs and shorter than 3 μs, respectively. Nanocrystals with a chemically modified surface are employed to demonstrate that energy transfer is governed by direct electron exchange. Magneto-optical experiments reveal the importance of the spin orientation of the exchanged electrons for the transfer rate. In the regime of intermediate temperatures (110–250 K) the transfer of excitation to the O2 dimer is resolved. © 2003 The American Physical Society.
2003, Physical Review B - Condensed Matter and Materials Physics, 68 (11), 1154051 - 11540511, English[Refereed]
Scientific journal
We report on a medium exhibiting extremely efficient light scattering properties: a liquid network formed in a porous matrix. Liquid fragments confined in the solid matrix result in a random fluctuation of the dielectric function and act as scattering objects for photons. The optical scattering efficiency is defined by the filling factor of the liquid in the pores and its dielectric constant. The spectral dependence of the scattering length of photons indicates that the phenomenon is governed by a Mie-type scattering mechanism. The degree of the dielectric disorder of the medium, i.e. the level of opacity is tunable by the ambient vapor pressure of the dielectric substance. In the strongest scattering regime the scattering length of photons is found to be in the micrometer range. By incorporation of dye molecules in the voids of the porous layer a system exhibiting optical gain is realized. In the multiple scattering regime the optical path of diffusively propagating photons is enhanced and light amplification through stimulated emission occurs: a strong intensity enhancement of the dye emission accompanied by significant spectral narrowing is observed above the excitation threshold for a layer being in the opalescence state.
2003, Proceedings of SPIE - The International Society for Optical Engineering, 5222, 67 - 77, English[Refereed]
International conference proceedings
Electro-chemical etching of heavily doped, (110) oriented, p+ (boron) doped silicon wafers results in porous silicon (PSi) layers which exhibit a strong in-plane anisotropy of the refractive index (birefringence). Single- and multiple layers of anisotropically nanostructured silicon (Si) have been fabricated and studied by polarization-resolved reflection and transmission measurements. Dielectric stacks of birefringent PSi acting as distributed Bragg reflectors have two distinct reflection bands depending on the polarization of the incident linearly polarized light. This effect is caused by a three-dimensional (in plane and in-depth) variation of the refraction index. The possibility of fine tuning the two orthogonally polarized reflection bands and their spectral splitting is demonstrated.
2003, Physica Status Solidi (A) Applied Research, 197 (2), 582 - 585, English[Refereed]
Scientific journal
The emission property of Si nanocrystals (nc-Si) in an optical microcavity was studied by photoluminescence (PL) and time resolved PL measurements. The PL from the microcavity was narrowed to the line width of 17 meV, enhanced by a factor of 20 compared to the same film without microcavity. The lifetime for nc-Si became shorter by putting the film in microcavity. This results could be well-explained by the redistribution of the optical modes in the cavity due to the presence of the optical resonator. © 2002 Elsevier Science B.V. All rights reserved.
2003, Physica E: Low-Dimensional Systems and Nanostructures, 17 (1-4), 451 - 452, English[Refereed]
Scientific journal
The optical properties of Si1-xGex alloy nanocrystals in a planar microcavity was investigated by using high-resolution transmission electron microscope (HRTEM). The photoluminescence lifetime was observed to be shortened by microcavity formation. The results showed that the luminescence intensity at the resonance wavelength was enhanced only in the normal direction while the intensity was supressed in other direction.
2003, Journal of Applied Physics, 93 (4), 2178 - 2181, English[Refereed]
Scientific journal
- Electronic Energy Transfer from Excitons Confined in Silicon Nanocrystals to Molecular Oxygen
We report on efficient electronic energy transfer from excitons confined in silicon (Si) nanocrystals to molecular oxygen (MO). The remarkable photosensitizing properties of Si nanocrystal assemblies result from a broad energy spectrum of photoexcited excitons, a long triplet exciton lifetime and a highly developed surface area. Quenching of photoluminescence (PL) of Si nanocrystals by MO physisorbed on their surface is found to be most efficient when the energy of excitons coincides with the triplet-singlet splitting energy of oxygen molecules. Spectroscopic analysis of the quenched PL spectrum evidences that energy transfer is accompanied by multi-phonon emission. From time-resolved measurements the characteristic time of energy transfer is found to be in the range of microseconds. The dependence of PL quenching efficiency on the surface termination of nanocrystals is consistent with short-range resonant electron exchange mechanism of energy transfer. The energy transfer to oxygen molecules in the gaseous phase at elevated temperatures is demonstrated.
2003, Materials Research Society Symposium - Proceedings, 770, 101 - 106, English[Refereed]
International conference proceedings
Photoluminescence (PL) properties of heavily P- and B-doped Si nanocrystals were studied. Strong room temeperature PL from nc-Si in borophosphosilicate glass (BPSG) thin films at around 0.9 eV was observed. It was found that the properties of the low-energy PL were different from those of exciton PL and dangling-bond-related PL. The luminescence peak energy of nc-Si was tuned from 0.9 eV to 2.0 eV by controlling the size and the impurity concentrations.
2003, Journal of Applied Physics, 94 (3), 1990 - 1995, English[Refereed]
Scientific journal
Optical extinction due to surface plasmon resonances of spherical and polyhedral carbon onions prepared from diamond nanoparticles has been studied. Extinction spectra for the onions dispersed in the distilled water were obtained experimentally by optical transmission spectroscopy. Theoretical considerations were given to interpret the experimental results. For spherical onions, a defective spherical onion model was introduced and the experimental extinction features were traced back to the aggregate of the defective spherical onions. The extinction spectrum with two peaks for the aggregate of polyhedral onions was reproduced by treating the planar segments of the onions as ellipsoidal graphite nanocrystals with crystalline anisotropy. The present study may allow us to address a long-standing important problem about an origin of the interstellar extinction bump.
AMER PHYSICAL SOC, Dec. 2002, PHYSICAL REVIEW B, 66 (24), English[Refereed]
Scientific journal
Optical extinction due to surface plasmon resonances of spherical and polyhedral carbon onions prepared from diamond nanoparticles has been studied. Extinction spectra for the onions dispersed in the distilled water were obtained experimentally by optical transmission spectroscopy. Theoretical considerations were given to interpret the experimental results. For spherical onions, a defective spherical onion model was introduced and the experimental extinction features were traced back to the aggregate of the defective spherical onions. The extinction spectrum with two peaks for the aggregate of polyhedral onions was reproduced by treating the planar segments of the onions as ellipsoidal graphite nanocrystals with crystalline anisotropy. The present study may allow us to address a long-standing important problem about an origin of the interstellar extinction bump. © 2002 The American Physical Society.
2002, Physical Review B - Condensed Matter and Materials Physics, 66 (24), 1 - 7[Refereed]
Scientific journal
We have prepared polyacrylonitrile (PAN) thin films containing Au nanoparticles by heat treatment of Au/PAN stacking films. The effect of heat treatment on the microstructure of the composite films was investigated by means of transmittance electron microscopy (TEM), Fourier-transform infrared (FT-IR) and Raman spectroscopy. The Au nanoparticles initially deposited on the PAN film were found to be dispersed into the PAN layer by heat treatment at 200°C, after which structural changes in the PAN matrix were observed, i.e. decomposition of methylene and nitrile groups into C=N conjugation. It was also found that heat treatment of the films at higher temperatures caused change of the PAN matrix into amorphous carbon. The mean size of the Au nanoparticles increased with increasing heat-treatment temperature. © 2002 Elsevier Science B.V. All rights reserved.
2002, Thin Solid Films, 408 (1-2), 59 - 63[Refereed]
Scientific journal
The optical properties of spherical and polyhedral carbon onions were studied in relation to the strong hump centered at 217.5 nm (4.6 μm-1) in the interstellar-dust extinction curve. The ultraviolet-visible absorption spectra of onions prepared by thermal annealing of diamond nanoparticles were measured. Theoretical calculations for the spherical and polyhedral carbon onions were also carried out to explain the experimental spectra. © 2002 MAIK "Nauka/Interperiodica".
2002, Physics of the Solid State, 44 (3), 450 - 453[Refereed]
Scientific journal
We report on light amplification through stimulated emission in a dielectrically disordered medium. Liquid fragments confined in the solid matrix of porous quartz layers result in a random fluctuation of the dielectric function, and dye molecules embedded in the voids yield optical gain. The level of opacity is tunable by the ambient vapor pressure of the dielectric substance. In the multiple scattering regime, a strong intensity enhancement of the dye emission accompanied by significant spectral narrowing is observed above the threshold for a layer being in the opalescence state. © 2002 The American Physical Society.
2002, Physical Review Letters, 89 (26)[Refereed]
Scientific journal
We report on a strong intrinsic optical anisotropy of silicon induced by dielectric nanopatterning. As a result, in-plane birefringence of anisotropically nanostructured (110) oriented Si is found to be 105 times larger than that observed in bulk silicon. The difference of the main values of the anisotropic refractive index (δn) exceeds that of any natural birefringent crystal. δn depends strongly on the typical size of the silicon nanowires assembling the layers and the dielectric constant of the medium surrounding these silicon nanoparticles. We show that dielectric stacks of anisotropically nanostructured Si can act as a dichroic distributed Bragg reflectors or optical microcavities. The reflection/transmission behavior of these structures is sensitive to the polarization of the incident linearly polarized light. These findings open the possibility of an application of optical devices based on birefringent silicon layers in a wide field.
2002, Optical Properties of Nanocrystals, 4808, 56 - 66[Refereed]
International conference proceedings
The efficient resonant energy transfer from excitons confined in silicon nanocrystals to molecular oxygen (MO) was demonstrated. It was found that the quenching of photoluminescence (PL) of silicon nanocrystals by MO physisorbed on their surface was most efficient when the energy of excitons coincided with triplet-singlet splitting energy of oxygen molecules. For achieving the high efficiency of the process, a highly developed surface of silicon nanocrystal assemblies and a long radiative lifetime of excitons were favorable.
2002, Physical Review Letters, 89 (13), 1374011 - 1374014[Refereed]
Scientific journal
We studied photoluminescence (PL) properties and PL decay-dynamics of Si nanoparticles fabricated by pulsed laser ablation of Si target in He gas. The as-deposited sample exhibited an emission peak at 2.1 eV at room temperature. After annealing for 20 min at 1100 °C in N 2 gas, the sample exhibited a peak at lower energies. As the distance between the substrate and the Si target increases (5-20 mm), PL peak shifts toward higher energies from 1.31 to 1.55 eV. We measured PL decay curves of each sample at different energy positions. For the 2.1 eV PL, only a very fast component (faster than our system response) was observed. For the 1.4 eV PL, we observed fast (<40 ns) and slow (>10 μs) components in all the decay curves detected at different energy positions. The lifetime of the slow component strongly depended on the detected energy positions. © 2002 Elsevier Science B.V. All rights reserved.
2002, Applied Surface Science, 197-198, 635 - 638[Refereed]
Scientific journal
Optical extinction due to surface plasmon resonances of spherical and polyhedral carbon onions prepared from diamond nanoparticles has been studied. Extinction spectra for the onions dispersed in the distilled water were obtained experimentally by optical transmission spectroscopy. Theoretical considerations were given to interpret the experimental results. For spherical onions, a defective spherical onion model was introduced and the experimental extinction features were traced back to the aggregate of the defective spherical onions. The extinction spectrum with two peaks for the aggregate of polyhedral onions was reproduced by treating the planar segments of the onions as ellipsoidal graphite nanocrystals with crystalline anisotropy. The present study may allow us to address a long-standing important problem about an origin of the interstellar extinction bump.
2002, Physical Review B - Condensed Matter and Materials Physics, 66 (24), 2454241 - 2454247[Refereed]
Scientific journal
The effects of P doping on photoluminescence (PL) properties of Si1-xGex alloy nanocrystals (nc-Si1-xGex) embedded in SiO2 thin films were studied. P doping resulted in a drastic decrease in the electron spin resonance (ESR) signals, which are assigned to the Si and Ge dangling bonds at interfaces between nc-Si1-xGex and matrices (Si and Ge Pb centers). It was found that, with increasing P concentration, the signal from Ge Pb centers is first quenched, and then the quenching of the signal from Si Pb centers starts. The quenching of the ESR signals was accompanied by a drastic enhancement of PL intensity. By further increasing P concentration, PL intensity became weaker. In this P concentration range, optical absorption due to the intravalley transition of free electrons generated by P doping appears. © 2002 Elsevier Science B.V. All rights reserved.
2002, Physica E: Low-Dimensional Systems and Nanostructures, 13 (2-4), 1034 - 1037[Refereed]
Scientific journal
Electronic states of P donors in Si nanocrystals (nc-Si) embedded in insulating glass matrices have been studied by electron spin resonance. Doping of P donors into nc-Si was demonstrated by the observation of optical absorption in the infrared region due to intraconduction band transitions. P hyperfine structure (hfs) was successfully observed at low temperatures. The observed splitting of the hfs was found to be much larger than that of the bulk Si:P and depended strongly on the size of nc-Si. The observed strong size dependence indicates that the enhancement of the hyperfine splitting is caused by the quantum confinement of P donors in nc-Si. © 2002 The American Physical Society.
2002, Physical Review Letters, 89 (20), 2068051 - 2068054[Refereed]
Scientific journal
We have prepared polyacrylonitrile (PAN) thin films containing Au nanoparticles by heat treatment of Au/PAN stacking films. The effect of heat treatment on the microstructure of the composite films was investigated by means of transmittance electron microscopy (TEM), Fourier-transform infrared (FT-IR) and Raman spectroscopy. The Au nanoparticles initially deposited on the PAN film were found to be dispersed into the PAN layer by heat treatment at 200 degreesC after which structural changes in the PAN matrix were observed, i.e. decomposition of methylene and nitrile groups into C=N conjugation. It was also found that heat treatment of the films at higher temperatures caused change of the PAN matrix into amorphous carbon. The mean size of the Au nanoparticles increased with increasing heat-treatment temperature. (C) 2002 Elsevier Science B.V. All rights reserved.
ELSEVIER SCIENCE SA, 2002, Thin Solid Films, 408 (1-2), 59 - 63, English[Refereed]
Scientific journal
Photoluminescence (PL) properties and PL decay dynamics of SiO 2 films containing Si nanocrystals (nc-Si) and Tm 3+ were studied. The samples exhibited a broad PL at around 1.5 eV due to the recombination of excitons in nc-Si, and rather sharp PL at 1.58, 0.84, and 0.69 eV corresponding to the intra-4f shell transitions of Tm 3+. The correlation between the intensities of nc-Si and Tm 3+ related PL was studied as a function of the Tm concentration, the size of nc-Si, and the temperature. It was found that the intensity of Tm 3+ related PL depends strongly on the size of nc-Si. At low temperatures, the spectral shape of nc-Si PL was strongly modified by doping Tm. From analysis of the modified spectral shape, a resonant energy transfer from nc-Si to Tm 3+ is discussed. © 2002 American Institute of Physics.
2002, Journal of Applied Physics, 92 (7), 4001 - 4006[Refereed]
Scientific journal
Photoluminescence (PL) properties of SiO2 films containing Si nanocrystals (nc-Si) and Nd3+ (Tm3+) were studied. The average size of nc-Si was changed in a wide range in order to tune the exciton energy of nc-Si to the energy separations between the discrete electronic states of Nd3+ (Tm3+). At room temperature, PL from the recombination of excitons confined in nc-Si and the intra-4f shell transition of Nd3+ (Tm3+) were observed simultaneously. The intensities of Nd3+ and Tm3+ PL were found to depend strongly on the size of nc-Si. These strong size-dependence suggests that nc-Si which are smaller than a threshold size can efficiently excite Nd3+ (Tm3+). We also studied the temperature dependence for the sample with Tm3+. At low temperature, PL spectra of the nc-Si was strongly modified. This modification gives the spectroscopic evidence of the resonant energy transfer to the third excited states of Tm3+. © 2002 Elsevier Science B.V. All rights reserved.
2002, Physica E: Low-Dimensional Systems and Nanostructures, 13 (2-4), 1038 - 1042[Refereed]
Scientific journal
Multilayer structures of anisotropically nanostructured (birefringent) silicon have been fabricated and studied by polarization-resolved reflection and transmission measurements. We demonstrate that stacks of birefringent porous silicon layers with alternating refractive indices and thicknesses act as dichroic Bragg reflectors or dichroic microcavities with a transmission/ reflection dependent on the polarization direction of the incident light. The possibility of separate fine tuning of two orthogonally polarized transmission/reflection bands and their spectral splitting is demonstrated. © 2002 American Institute of Physics.
2002, Journal of Applied Physics, 91 (10 I), 6704 - 6709[Refereed]
Scientific journal
Carbon onions prepared by high temperature annealing of ultradispersed diamond nanoparticles of about 5 nm in average diameter have been studied by X-ray diffraction using synchrotron radiation. The X-ray diffraction patterns show transformation of the diamond nanoparticles with sp3 bonds into spherical carbon onions containing remaining diamond-like core and then into polyhedral onions with facets on their outer part and pure sp2 graphitic bonds. The prepared onions form concentric-shell particles which comprise of about ten shells with an intershell distance of 0.35-0.36 nm. The large intershell distance suggests a considerable reduction in intershell interaction when compared to perfect graphite. The X-ray data are related to the previously performed studies by electron energy-loss spectroscopy and electron spin resonance. © 2002 Elsevier Science Ltd. All rights reserved.
2002, Carbon, 40 (9), 1469 - 1474[Refereed]
Scientific journal
- Resonant excitation of Er3+ by the energy transfer from Si nanocrystals
Photoluminescence (PL) properties of SiO2 films containing Si nanocrystals (nc-Si) and Er were studied. The average size of nc-Si was changed in a wide range in order to tune the exciton energy of nc-Si to the energy separations between the discrete electronic states of Er3+. PL from exciton recombination in nc-Si and the intra-4f shell transition of Er3+ were observed simultaneously. At low temperatures, periodic features were observed in the PL spectrum of nc-Si. The period agreed with the optical phonon energy of Si. The appearance of the phonon structures implies that nc-Si which satisfy the energy conservation rule during the energy transfer process can resonantly excite Er3+. The mechanism of the energy transfer from nc-Si to Er3+ is discussed on the basis of the PL features.
SPRINGER-VERLAG BERLIN, 2001, Proceedings of the 25th International Conference on the Physics of Semiconductors, Pts I and Ii, 87, 1177 - 1178, English[Refereed]
International conference proceedings
- Raman scattering by electron-hole excitations in silver nanocrystals
Raman scattering experiments from silver nanocrystals embedded in films of amorphous silica are reported. In addition to the low-frequency peak due to vibrational quadrupolar modes, a broadband is observed in the high-frequency range, with a maximum at about 1000 cm-1. The linear dependence of the position of this maximum on the inverse cluster radius is in agreement with Raman scattering by single or collective electron-hole excitations.
2001, Physical Review B - Condensed Matter and Materials Physics, 63 (23), 2334021 - 2334024[Refereed]
Scientific journal
Photoluminescence (PL) properties of SiO2 films containing Si nanocrystals (nc-Si) and Er were studied. The average size of nc-Si was changed in a wide range in order to tune the exciton energy of nc-Si to the energy separations between the discrete electronic states of Er3+. PL from exciton recombination in nc-Si and the intra-4f shell transition of Er3+ were observed simultaneously. At low temperatures, periodic features were observed in the PL spectrum of nc-Si. The period agreed well with the optical phonon energy of Si. The appearance of the phonon structure implies that nc-Si which satisfy the energy conservation rule during the energy transfer process can resonantly excite Er3+. For the PL from Er3+, a delay was observed after the pulsed excitation of nc-Si hosts. The rise time of the PL showed strong size dependence. The effects of the quantum confinement of excitons in nc-Si on the energy transfer process are discussed. © 2001 American Institute of Physics.
2001, Journal of Applied Physics, 90 (9), 4761 - 4767[Refereed]
Scientific journal
The investigation of the structure and electronic properties of carbon onions was presented. It was shown that diamond nanoparticles are transformmed into spherical carbon onions on annealing at 1700°C by high-resolution transmission electron microscopy (HRTEM).On studying HRTEM, Raman spectroscopy and electron spin resonance, the presence of π electrons was depicted. It was suggested that the spherical onions consist of small domain of graphite sp2 sheets dangling bond defects in the peripheries.
2001, Journal of Chemical Physics, 114 (17), 7477 - 7482[Refereed]
Scientific journal
The low-frequency plasmon-resonant Raman scattering by the vibrational modes of silver nanoclusters embedded in amorphous SiO2 films is studied experimentally and theoretically. By electron microscopy it is observed that the concentration of defects in nanocrystals decreases and the intensity of Raman scattering increases by thermal annealing. It is shown that the degree of spatial coherence inside clusters has a strong effect on the Raman intensity and on its frequency dependence. © 2001 The American Physical Society.
2001, Physical Review B - Condensed Matter and Materials Physics, 63 (7), 0754051 - 0754056[Refereed]
Scientific journal
- Size-dependent photoluminescence from oxidized Si nanocrystals in a weak confinement regime
We have studied photoluminescence (PL) from surface-oxidized Si nanocrystals (nc-Si) as a function of the size (2.5-9.0 nm in diameter). As the size decreased, a high-energy shift, of the PL peak in a wide range from the vicinity of the bulk band gap to the visible region was observed for the first time. This PL shift was accompanied by the shortening of the PL lifetime and the increase in the exchange splitting energy of excitons. These size dependences indicate that the PL originates from the recombination of excitons confined in nc-Si. The differences in the PL properties between H-terminated and surface-oxidized nc-Si are also discussed.
SPRINGER-VERLAG BERLIN, 2001, Proceedings of the 25th International Conference on the Physics of Semiconductors, Pts I and Ii, 87, 1223 - 1224, English[Refereed]
International conference proceedings
Very thin Nylon 11 films (≤20nm in thickness) containing Au or Ge nanoparticles (Au/Nylon 11 or Ge/Nylon 11) were prepared by a thermal relaxation technique, and current-voltage (I-V) characteristics in the vertical direction of the films were studied. In the case of Au/Nylon 11, the plan and cross-sectional transmission electron microscopic (TEM) images revealed that Au nanocrystals are spontaneously aligned in the middle of the upper and lower electrodes and Nylon 11 tunneling barriers are formed between Au nanocrystals and electrodes. In the case of Ge/Nylon 11, lattice fringes corresponding to Ge crystals with the diamond structure were not observed in TEM images, suggesting that amorphous Ge particles are dispersed in Nylon 11 films. Clear Coulomb staircases were observed in the I-V characteristics in both cases. KEYWORDS.
2001, Japanese Journal of Applied Physics, Part 2: Letters, 40 (3 B), 1911 - 1914[Refereed]
Scientific journal
Photoluminescence (PL) of SiO2 films co-doped with Si nanocrystals (nc-Si) and Er was studied. The average size of nc-Si was changed in a wide range in order to tune the exciton energy of nc-Si to the energy separations between the discrete electronic states of Er3+. PL from exciton recombination in nc-Si and the intra-4f shell transition of Er3+ were observed simultaneously. At low temperatures, periodic features were observed in the PL spectrum of nc-Si. The period agreed well with the optical phonon energy of Si. The appearance of the phonon structures implies that nc-Si which satisfy the energy conservation rule during the energy transfer process can resonantly excite Er3+. The effects of the quantum confinement of excitons in nc-Si on the energy transfer process are discussed.
2001, Materials Research Society Symposium - Proceedings, 638 (9), 1177 - 1178[Refereed]
International conference proceedings
Raman investigation of metal nanoparticles embedded in either a glass or silica matrix was carried out. New low-frequency Raman bands in the 3-40 cm-1 range were observed in these nanoparticles. These bands were ascribed to light scattering by the nanoparticle radial modes: the breathing mode and its harmonics.
2001, Journal of Chemical Physics, 115 (8), 3444 - 3447[Refereed]
Scientific journal
- Raman scattering by electron-hole excitations in silver nanocrystals
Raman scattering experiments from silver nanocrystals embedded in films of amorphous silica are reported. In addition to the low-frequency peak due to vibrational quadrupolar modes, a broadband is observed in the high-frequency range, with a maximum at about 1000 cm(-1). The linear dependence of the position of this maximum on the inverse cluster radius is in agreement with Raman scattering by single or collective electron-hole excitations.
AMER PHYSICAL SOC, 2001, Physical Review B, 63 (23), art. no. - 233402, English[Refereed]
Scientific journal
- Photoluminescence from n- (p-) type impurity doped Si nanocrystals
Effects of impurity (P and B) doping on the photoluminescence (PL) properties of Si nanocrystals (nc-Si) in SiO2 thin films are studied. It is shown that with increasing P concentration, PL intensity first increases and then decreases. In the P concentration range where PL intensity increases, quenching of the defect-related PL is observed, suggesting that dangling-bond defects are passivated by P doping. On the other hand, in the range where PL intensity decreases, optical absorption due to the intravalley transitions of free electrons generated by P doping appears. The generation of free electrons and the resultant three-body Auger recombination of electron-hole pairs is considered to be responsible for the observed PL quenching. In the case of B doping, the behavior is much different. With increasing B concentration, PL intensity decreases monotonously. By combining the results obtained for P and B doped samples, the effects of donor and acceptor impurities on the PL properties of nc-Si are discussed.
2001, Materials Research Society Symposium - Proceedings, 638[Refereed]
International conference proceedings
We have studied photoluminescence (PL) from surface-oxidized Si nanocrystals (nc-Si) as a function of the size (4.2-9.0 nm in diameter). As the size decreased, a high-energy shift of the PL peak from the vicinity of the bulk band gap to the visible region was observed for the first time. This PL shift was accompanied by the shortening of the PL lifetime and the increase in the exchange splitting energy of excitons.
2001, Physica Status Solidi (B) Basic Research, 224 (1), 229 - 232[Refereed]
Scientific journal
- Photoluminescence and ESR study of Si
1-x Gex alloy nanocrystalsDangling bond defects in Si1-xGex alloy nanocrystals (nc-Si1-xGex) as small as 4 nm in diameter embedded in SiO2 thin films were studied by electron spin resonance (ESR), and the effects of the defects on photoluminescence (PL) properties were discussed. It was found that the ESR spectrum is a superposition of signals from Si and Ge dangling bonds at the interfaces between nc-Si1-xGex and SiO2 matrices (Si and Ge Pb centers). As Ge concentration increased, the intensity of the signal from the Ge Pb centers increased, while that from the Si Pb centers was almost independent of Ge concentration. The increase in the number of Ge Pb centers was accompanied by strong quenching of the PL. The observed correlation between the two measurements suggests that Ge Pb centers act as efficient non-radiative recombination centers for photogenerated carriers, resulting in the quenching of the PL.
2001, Materials Research Society Symposium - Proceedings, 638[Refereed]
International conference proceedings
Nanogranular thin films consisting of Ni1-xCox alloy nanoparticles separated by graphitic matrices are fabricated by a co-sputtering method. The structure and magnetic properties of the films are studied. An improvement in their magnetic properties by optimizing the alloy ratio will be demonstrated. Transmission electron microscopic (TEM) observation shows nanoparticles with a small mean diameter (∼ 7 nm) and narrow size distribution (∼ 20% of mean diameter) at the Co/(Ni + Co) ratio (x) ranging from 0 to 0.83. In this region, the coercivity continuously increases with x and manifests a maximum value of 907 Oe at x = 0.83. The increase can be explained in terms of alloy formation. With further increasing x up to x = 1, the coercivity decreases. The decrease is caused by the existence of extremely large Co particles, which are revealed by TEM observation.
2001, Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers, 40 (11), 6370 - 6374[Refereed]
Scientific journal
- Internal photoemission from Ag nanoparticles embedded in Al
2 O3 filmPhotocurrent properties of Al2O3 films containing Ag particles a few nanometers in diameter were studied. In the dark, the films exhibit T-1/2 dependence of ln(σ), where σ and T are the conductivity and temperature, respectively. This dependence indicates that the electron transport is carried out by thermally activated electron tunneling between Ag nanoparticles. Under UV-light irradiation, the photocurrent produced in the films was observed. The photocurrent could be well explained by the internal photoemission from Ag nanoparticles and/or electrodes.
2001, Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers, 40 (9 A), 5389 - 5393[Refereed]
Scientific journal
Photocurrent properties of Al2O3 films containing Ag particles a few nanometers in diameter were studied. In the dark, the films exhibit T-1/2 dependence of ln(sigma), where sigma and T are the conductivity and temperature, respectively. This dependence indicates that the electron transport is carried out by thermally activated electron tunneling between Ag nanoparticles. Under UV-fight irradiation, the photocurrent produced in the films was observed. The photocurrent could be well explained by the internal photoemission from Ag nanoparticles and/or electrodes.
INST PURE APPLIED PHYSICS, 2001, Japanese Journal of Applied Physics Part 1-Regular Papers Short Notes & Review Papers, 40 (9A), 5389 - 5393, English[Refereed]
Scientific journal
We performed a study of the in-plane birefringence of anisotropically nanostructured Si layers, which exhibit a greater difference in the main value of the anisotropic refractive index than that of natural birefringent crystals. The anisotropy parameters were found to be strongly dependent on the typical size of the Si nanowires used to assemble the layers. This finding opens the possibility of an application of birefringent Si retarders to a wide spectral range for control of the polarization state of light. © 2001 Optical Society of America.
2001, Optics Letters, 26 (16), 1265 - 1267[Refereed]
Scientific journal
Photoluminescence (PL) properties of SiO2 films containing Si nanocrystals (nc-Si) and Tm3+ were studied. The average size of nc-Si was changed over wide range in order to tune the exciton energy of nc-Si to the energy separations between the discrete electronic states of Tm3+. At room temperature, the samples exhibited broad PL peaks located at an energy region between 1.35 and 1.6 eV corresponding to the recombination of the excitons in nc-Si, and sharp peaks at 1.57 and 0.69 eV corresponding to the intra-4f shell transition of Tm3+. The intensity of the Tm3+ related PL showed a strong dependence on the size of nc-Si. This result implies that only nc-Si which are smaller than a threshold size can efficiently excite Tm3+. At low temperatures, the spectral shape of nc-Si PL was strongly modified by doping Tm. From the analysis of the modified spectral shape, the spectroscopic evidence of the resonant energy transfer from nc-Si to Tm3+ was obtained. © 2001 Elsevier Science B.V. All rights reserved.
2001, Physica B: Condensed Matter, 308-310, 1121 - 1124[Refereed]
Scientific journal
Incorporation of Si nanocrystals (nc-Si) into Er-doped glasses strongly enhances the infrared luminescence of Er3+. The enhancement is believed to be due to the energy transfer from nc-Si. However, the mechanism of the interaction between nc-Si and Er3+ has not been fully understood. In this work, we have studied the interaction between nc-Si and Er3+ by photoluminescence (PL) spectroscopy and PL decay dynamics. In order to tune the luminescence (bandgap) energy of nc-Si to the energy separations between the discrete electronic states of Er3+, the size of nc-Si was changed in a wide range; the PL energy of nc-Si was changed from 1.2 to 1.5 eV. At low temperatures, periodic features were observed in the PL spectra of nc-Si. The observation of the features is the first spectroscopic evidence that indicates the strong coupling between nc-Si and Er3+. Furthermore, size dependence of the energy transfer rate was estimated from the delay time of the Er3+ PL. The effects of quantum confinement of excitons in nc-Si on the high PL efficiency of Er3+ are discussed.
2001, Rare-Earth-Doped Materials and Devices V, 4282, 153 - 167[Refereed]
International conference proceedings
- Enhancement of the Faraday rotation
The enhancement of the Faraday rotation is achieved by the following methods. 1) The Faraday rotation is enhanced approximately twofold by fabricating thin films containing fine iron particles, compared with continuous iron films. 2) After fabricating periodical groove structures on transparent substrates, thin films containing fine iron particles are deposited on the substrates using the evaporation method in gases. A large Faraday rotation about 60 times larger than that of continuous iron films with the same thickness is obtained. In the second case, a light intensity dependence is found.
2001, Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers, 40 (11), 6365 - 6369[Refereed]
Scientific journal
Dangling bond defects in Si1 - xGex alloy nanocrystals (nc-Si1 - xGex) as small as 4 nm in diameter embedded in SiO2 thin films were studied by electron spin resonance (ESR), and the effects of the defects on photoluminescence (PL) properties were discussed. It was found that the ESR spectrum is a superposition of signals from Si and Ge dangling bonds at the interfaces between nc-Si1 - xGex and SiO2 matrices (Si and Ge Pb centers). As the Ge concentration increased, the signal from the Ge Pb centers increased, while that from the Si Pb centers was nearly independent of Ge concentration. The increase in the number of Ge Pb centers was accompanied by strong quenching of the PL. The observed correlation between the two measurements suggests that the Ge Pb centers act as efficient nonradiative recombination centers for photogenerated carriers, resulting in the quenching of the main PL. © 2001 American Institute of Physics.
2001, Journal of Applied Physics, 89 (9), 4917 - 4920[Refereed]
Scientific journal
The effects of P doping on photoluminescence (PL) properties of Si1-xGex alloy nanocrystals (nc-Si1-xGex in SiO2 thin films were studied. P doping drastically decreases the electron spin resonance (ESR) signals that are assigned to the Si and Ge dangling bonds at the interfaces between nc-Si1-xGex and SiO2 matrices (Si and Ge Pb centers). With increasing P concentration, the signal from the Ge Pb centers are first quenched, and then the signal from the Si Pb centers start to be quenched. The quenching of the ESR signals is accompanied by a drastic enhancement of the PL intensity. The PL intensity has a maximum at a certain P concentration, which depends on the Si:Ge ratio. By further increasing the P concentration, the PL intensity becomes weaker. In this P concentration range, optical absorption emerges due to the intravalley transition of free electrons generated by the P doping. The observation of the free-electron absorption provides direct evidence that carriers in nanometer-sized Si1-xGex alloy crystals can be controlled by impurity doping. © 2001 American Institute of Physics.
2001, Journal of Applied Physics, 90 (10), 5147 - 5151[Refereed]
Scientific journal
The effects of P doping on defects in Si1-xGex alloy nanocrystals (nc-Si1-xGex) embedded in SiO2 thin films were studied by electron spin resonance (ESR) and photoluminescence (PL) spectroscopy. P doping resulted in a drastic decrease in the ESR signals, which are assigned to the Si and Ge dangling bonds at the interfaces between nc-Si1-xGex and matrices (Si and Ge Pb centers). It was found that, with increasing P concentration, the signal from Ge Pb centers is first quenched, and then the quenching of the signal from Si Pb centers starts. The quenching of the ESR signals was accompanied by a drastic enhancement of PL intensity. © 2001 Elsevier Science B.V. All rights reserved.
2001, Physica B: Condensed Matter, 308-310, 1100 - 1103[Refereed]
Scientific journal
- Size-dependent photoluminescence from surface-oxidized Si nanocrystals in a weak confinement regime
Photoluminescence (PL) from surface-oxidized Si nanocrystals (nc-Si) was studied as a function of the size. The size of nc-Si was comparable with or larger than the Bohr radius of free excitons in bulk Si crystal (5 nm). In contrast to smaller surface-oxidized nc-Si (typically as small as a few nanometers in diameter), these relatively large nc-Si exhibited PL properties with strong size dependence. A high-energy shift of the PL peak from the vicinity of the bulk band gap to the visible region was observed. This PL shift was accompanied by a shortening of the PL lifetime and an increase in the exchange splitting energy of excitons. These size dependences indicate that the PL originates from the recombination of excitons confined in nc-Si. The differences in the PL properties between H-terminated and surface-oxidized nc-Si are also discussed.
AMER PHYSICAL SOC, Dec. 2000, PHYSICAL REVIEW B, 62 (24), 16820 - 16825, English[Refereed]
Scientific journal
- Photoluminescence and free-electron absorption in heavily phosphorus-doped Si nanocrystals
Heavily phosphorus-doped Si nanocrystals several nanometers in diameter are studied by photoluminescence (PL) and optical absorption spectroscopy. It is demonstrated that P doping results in the quenching of the FL. The quenching is accompanied by the appearance of the optical absorption in the infrared range. The absorption was assigned to the intravalley transitions of free electrons generated by P doping (free-electron absorption). The generation of free electrons and the resultant three-body Auger recombination of excitons is considered to be responsible for the observed PL quenching.
AMER PHYSICAL SOC, Nov. 2000, PHYSICAL REVIEW B, 62 (19), 12625 - 12627, English[Refereed]
Scientific journal
- SPRINGER, 2000, Frontiers of Nano-Optoelectronic Systems, 6, 303 - 317, EnglishVisible and infrared photoluminescence from deposited germanium-oxide clusters and from Ge nanocrystals
[Refereed]
International conference proceedings
We have demonstrated the transformation of spherical carbon onions to diamond by low-temperature heat treatment. Carbon onions were prepared by 1700 °C annealing of diamond nanoparticles. High-resolution transmission electron microscopy (HRTEM) and X-ray diffraction showed that diamond nanoparticles transformed into the carbon onions and no trace of diamond was detected after the annealing. Carbon onions were subsequently heat treated at 500 °C in air. HRTEM images showed that diamond particles several tens of nanometers in diameter as well as the carbon onions coexist after the heat treatment in air. The results suggest that the onions transformed to diamond at a low-temperature under atmospheric pressure without electron and ion irradiation. From detailed HRTEM and electron energy-loss spectroscopy studies, sp3 sites in the onions and oxygen during the heat treatment are considered to play important roles in the transformation without any irradiation.
2000, Diamond and Related Materials, 9 (3), 856 - 860[Refereed]
Scientific journal
A method for fabricating thin films of carbon nanocapsules and onion-like graphitic particles was reported. The method consists of cosputtering Ni and graphite, and subsequent thermal annealing in vacuum. Transmission electron microscopic and Raman studies revealed that the films were composed of Ni-filled carbon nanocapsules with graphitic coatings several nanometers in thickness. Ni particles were removed by acid etching, resulting in the formation of thin films composed of onion-like graphitic particles. Electron field emission properties of the onion-like graphitic-particle films were studied. ©2000 The Japan Society of Applied Physics.
2000, Japanese Journal of Applied Physics, Part 1: Regular Papers and Short Notes and Review Papers, 39 (12 A), 6680 - 6683[Refereed]
Scientific journal
Photoluminescence (PL) from surface-oxidized Si nanocrystals (nc-Si) was studied as a function of the size. The size of nc-Si was comparable with or larger than the Bohr radius of free excitons in bulk Si crystal (5 nm). In 'contrast to smaller surface-oxidized nc-Si (typically as small as a few nanometers in diameter), these relatively large nc-Si exhibited PL properties with strong size dependence. A high-energy shift of the PL peak from the vicinity of the bulk band gap to the visible region was observed. This PL shift was accompanied by a shortening of the PL lifetime and an increase in the exchange splitting energy of excitons. These size dependences indicate that the PL originates from the recombination of excitons confined in nc-Si. The differences in the PL properties between H-terminated and surface-oxidized nc-Si are also discussed.
2000, Physical Review B - Condensed Matter and Materials Physics, 62 (24), 16820 - 16825[Refereed]
Scientific journal
Electrical transport properties of extremely thin phosphosilicate glass (PSG) films containing Si nanocrystals (nc-Si) a few nanometers in diameter were studied. Samples were prepared by cosputtering Si and PSG targets, and post-annealing. Periodic Coulomb staircases were clearly observed in the DC current-voltage (I-V) characteristics along the vertical direction of films. Although the step structure was broadened with increasing temperature, it remained up to 200 K. The I-V curve could be well fitted by Monte Carlo simulation with a simple double-barrier structure model. Advantages of using PSG instead of SiO2 as surrounding matrices of nc-Si to observe single-electron tunneling effects are discussed.
2000, Physica E: Low-Dimensional Systems and Nanostructures, 7 (3), 444 - 447[Refereed]
Scientific journal
Very thin Nylon 11 films (≤20 nm in thickness) containing Au nanoparticles were prepared, and current-voltage (I-V) characteristics in the vertical direction of the films were studied. The plan and cross-sectional transmission electron microscopic images revealed that Au particles are spontaneously aligned in the middle of the upper and lower electrodes and Nylon 11 tunneling barriers are naturally formed between Au nanoparticles and electrodes. Clear Coulomb staircases were observed in the I-V characteristics.
2000, Thin Solid Films, 372 (1), 169 - 172[Refereed]
Scientific journal
Composite thin films consisting of nano-sized Ag particles dispersed in nylon 11 thin films have been prepared by using a thermal relaxation technique. The films obtained were characterized by transmission electron microscopy (TEM), electron diffraction (ED), energy-dispersive X-ray (EDX) microanalysis, and optical absorption spectroscopy. The Ag nanoparticles with 4.5-9.1 nm in diameter were found to be isolated individually and dispersed uniformly in the nylon 11 matrix. The volume fraction and the mean size of Ag nanoparticles in the film could be controlled by varying the initial amount of Ag deposition. Optical absorption peak due to the surface plasmon resonance of the Ag particles were observed around 430 nm and shifted to a longer wavelength with increasing the mean size of Ag nanoparticles, and absorbance increased simultaneously. We have also prepared Ag2S nanoparticles with 4.7-11.2 nm in diameter in nylon 11 films from exposing the Ag/nylon 11 films to H2S/O2 mixed gas. ED patterns of the particles formed after the reaction with H2S were completely indexed as those of β-Ag2S with a monoclinic structure. The onset of the optical absorption spectra is similar to that of bulk β-Ag2S, suggesting that Ag2S nanoparticles with diameter of ca. 5 nm preserve the band structure of bulk Ag2S.
2000, Thin Solid Films, 359 (1), 55 - 60[Refereed]
Scientific journal
Photoluminescence (PL) from (Formula presented) alloy nanocrystals (Formula presented) as small as 4-5 nm in diameter was studied as a function of the Ge content. The (Formula presented) samples were fabricated by the cosputtering of Si, Ge, and (Formula presented) and postannealing at (Formula presented) High-resolution transmission electron microscopy, electron diffraction, and Raman spectroscopy clearly showed the growth of spherical (Formula presented) nanocrystals in (Formula presented) matrices. The PL spectra of (Formula presented) were found to be very sensitive to the Ge content. A low-energy shift of the PL peak from the widened band gap of Si nanocrystals to that of Ge nanocrystals with increasing Ge content was clearly observed. © 2000 The American Physical Society.
2000, Physical Review B - Condensed Matter and Materials Physics, 61 (23), 15988 - 15992[Refereed]
Scientific journal
Photoluminescence (PL) spectra of Si nanocrystals (nc-Si) in phosphosilicate glass matrices, and the PL decay dynamics were studied. The 1.4 eV peak corresponding to the recombination of electron-hole pairs confined in nc-Si (band-edge PL) became intense with increasing the P concentration in the matrix region, while the 0.9 eV peak related to the defects at the interfaces between nc-Si and matrices became weaker. The lifetime of the band-edge PL increased with the P concentration. These results indicate that the improvement of the band-edge PL efficiency is achieved by decreasing the interface defect density by P doping.
2000, Journal of Luminescence, 87, 429 - 431[Refereed]
Scientific journal
Photoluminescence decay dynamics of SiO2 films containing Si nanocrystals (nc-Si) and Er was studied. On increasing the Er concentration, the 1.54 μm PL due to the intra-4f shell transition of Er3+ increased drastically, while the PL peak at 0.8 μm due to the recombination of electron-hole pairs in nc-Si decreased and the lifetime became shorter. For the 1.54 μm PL, PL delay was observed after the pulsed excitation of nc-Si host. The results clearly indicated that Er3+ is excited by the energy transfer from nc-Si. From the observed PL delay, the energy transfer rate from nc-Si to Er3+ was estimated to be 5 × 105 s-1.
2000, Journal of Luminescence, 87, 426 - 428[Refereed]
Scientific journal
Heavily phosphorus-doped Si nanocrystals several nanometers in diameter are studied by photoluminescence (PL) and optical absorption spectroscopy. It is demonstrated that P doping results in the quenching of the PL. The quenching is accompanied by the appearance of the optical absorption in the infrared range. The absorption was assigned to the intravalley transitions of free electrons generated by P doping (free-electron absorption). The generation of free electrons and the resultant three-body Auger recombination of excitons is considered to be responsible for the observed PL quenching.
2000, Physical Review B - Condensed Matter and Materials Physics, 62 (19), 12625 - 12627[Refereed]
Scientific journal
SiO2 and phosphosilicate glass (PSG) films containing Si nanocrystals (nc-Si) as small as a few nanometers were studied by electron spin resonance (ESR) and photoluminescence (PL), and the correlation between the two measurements was examined. It is shown that the incorporation of nc-Si in SiO2 results in the drastic increase in the ESR signal; the signal is assigned to the Si dangling bonds at the interfaces between nc-Si and matrices (Pb, centers). The ESR signal becomes weaker by doping P into SiO2 matrices, i.e., by using PSG as matrices. By increasing the P concentration, the ESR signal decreases further. By decreasing the ESR signal, the low-energy PL peak at 0.9 eV decreases, while the band-edge PL at 1.4 eV increases. These results suggest that the 0.9 eV peak is related to Ph centers, and that the decrease in the density of the Pb centers by P doping brings about an improvement in the band-edge PL efficiency of nc-Si. © 2000 American Institute of Physics.
2000, Journal of Applied Physics, 87 (4), 1855 - 1857[Refereed]
Scientific journal
Co filled carbon nanocapsules, which are formed by a heat treatment of the mixture of Co and diamond nanoparticles, have been studied by in situ transmission electron microscopy (TEM), x-ray diffraction, and Raman spectroscopy. Raman studies show that the heat treatment reduces the surface native oxide (Co3O4) of Co nanoparticles. The reduction is accompanied by graphitization of diamond nanoparticles, indicating that diamond nanoparticles being in contact with the metallic Co are transformed into graphitic coating. The in situ TEM studies show that the graphitic coating is formed in the heating process, not in the cooling process. Furthermore, once the coating is completed, the number of the graphitic layers is almost constant on further heating and cooling. These results allow us to conclude that metallic Co particles simply act as templates for graphitic coating. © 2000 American Institute of Physics.
2000, Journal of Applied Physics, 88 (9), 5452 - 5456[Refereed]
Scientific journal
SiGe alloy nanocrystals (nc-Si1-xGex) as small as 4-5 nm in diameter were prepared and their photoluminescence (PL) properties were studied as a function of the Ge content. The growth of nc-Si1-xGex in SiO2 matrices was confirmed by high-resolution transmission electron microscopy, electron diffraction and Raman spectroscopy. The PL spectra of nc-Si1-xGex were found to be sensitive to the Ge content. For the sample without Ge doping, a PL peak was observed at around 1.45 eV; the peak was assigned to the radiative recombination of electron-hole pairs confined in Si nanocrystals. As the Ge content increased, the PL peak shifted to lower energies although the average diameter of nc-Si1-xGex was almost the same for all the samples. This result indicates that the Ge doping is an effective method to control the band gap energy of Si nanocrystals.
2000, Journal of Luminescence, 87, 350 - 352[Refereed]
Scientific journal
Resonant photoluminescence From Si1-xGex alloy nanocrystals as small as 4 nm in diameter embedded in SiO2 thin film matrices was studied. In pure Si nanocrystals, phonon structures were clearly observed, indicating that optical transitions are assisted by momentum-conserving phonons. These structures are quenched by adding a small amount of Ge atoms in Si nanocrystals, i.e., due to the formation of Si1-xGex alloy. Furthermore, the lifetime of the radiative recombination became much faster in doped nanocrystals. These results suggest that Si1-xGex alloy formation leads to a disorder in the translation invariance of the crystalline lattice, thus resulting in the breakdown of the k-conservation rule. © 2000 American Institute of Physics.
2000, Journal of Applied Physics, 88 (10), 5772 - 5776[Refereed]
Scientific journal
A new and simple method for synthesizing graphitic carbon-coated magnetic-metal (Co, Ni and Fe) nanoparticles has been reported. The mixture of metal and diamond nanoparticles was just annealed at 1700°C in vacuum. The annealed samples were studied by high-resolution transmission electron microscopy, selected-area electron diffraction and X-ray diffraction. These analyses revealed that magnetic-metal particles are coated with uniform graphitic layers several nanometers in thickness.
2000, Chemical Physics Letters, 316 (5-6), 361 - 364[Refereed]
Scientific journal
Electrical transport properties of extremely thin phosphosilicate glass (PSG) films containing Si nanocrystals (nc-Si) a few nanometers in diameter were studied. Samples were prepared by cosputtering Si and PSG targets, and post annealing. Periodic Coulomb staircases were clearly observed in the dc current-voltage (I-V) characteristics along the vertical direction of films. Although the step structure was broadened with increasing the temperature, it remained up to 200 K. The 1-V curve could be well fitted by Monte Carlo simulation with a simple double-barrier structure model. Advantages of using PSG instead of SiO2 as surrounding matrices of nc-Si to observe single-electron tunneling effects are discussed. © 1999 American Institute of Physics.
1999, Journal of Applied Physics, 86 (6), 3199 - 3203[Refereed]
Scientific journal
Electrical transport properties of extremely thin metal (Ag and Au) granular films fabricated by a cosputtering method were studied. High-resolution transmission electron microscopic observations revealed that Ag (Au) nanocrystals several nanometers in diameter were dispersed in thin films. In spite of the large size (100×100 μm2) of the devices prepared, the Coulomb blockade and the Coulomb staircase were observed on current-voltage (I-V) characteristics at relatively high temperature (100 K). Although the samples were prepared under the same conditions, the I-V curves varied from sample to sample. The observed I-V curves were well fitted by Monte Carlo simulation assuming that the samples consist of a few serial and parallel connections of nanocrystals. The present results suggest that the macroscopic conduction of thin granular films is dominated by only a few special conduction paths.
1999, Thin Solid Films, 349 (1), 289 - 292[Refereed]
Scientific journal
Boron-doped Si nanocrystals (nc-Si) as small as 2.7-3.8 nm in diameter were prepared and their photoluminescence (PL) properties were studied as functions of B concentration, size and excitation power. As the B concentration increased, the PL intensity decreased rapidly. The degree of PL quenching was found to increase with increasing size. In the case of undoped nc-Si, saturation and blue shift of PL peak were observed with increasing excitation power. However, these effects were not observed for heavily B-doped samples. The importance of the nonradiative Auger recombination process in B-doped nc-Si is discussed. © 1999 Elsevier Science Ltd.
1999, Solid State Communications, 109 (9), 561 - 565[Refereed]
Scientific journal
Dispersion of nanocrystalline Si (nc-Si) in phosphosilicate glass thin films were prepared and photoluminescence (PL) properties were studied in the near-infrared region. The nanocrystals exhibited band-edge PL at 1.4 eV at room temperature, whose intensity increased with increasing P concentration, and quenched defect-related PL at 0.9 eV at low temperature. The enhancement of the band-edge PL was attributed to a decrease of the number of interface defects with the incorporation of P atoms in surrounding oxide matrices. Thus, P doping is an effective method for improving band-edge PL efficiency of nc-Si.
1999, Applied Physics Letters, 75 (2), 184 - 186[Refereed]
Scientific journal
Photoluminescence (PL) properties of SiO2 films containing Si nanocrystals (nc-Si) and Er3+ (Yb3+) were studied. PL peaks attributable to the recombination of electron-hole pairs in nc-Si (∼1.5 eV) and the intra-4 f shell transition of Er3+ (∼0.81eV) (Yb3+ (∼1.26eV)) were observed simultaneously at room temperature. Correlation of the two peaks was studied as a function of nanocrystalline size. It was found that the intensity of the Er3+-related (Yb3+-related) peak increases drastically as the size of nc-Si decreases. Temperature dependence of PL spectra was studied. In the case of Yb-doped samples, temperature quenching of the PL became small as the size decreased, while in the case of Er-doped samples, no remarkable temperature dependence was observed. Two major features of the quantum size effects of nc-Si, i.e., the band-gap widening and the increase in the PL efficiency with decreasing the size, are thought to contribute to the improvement of room temperature PL efficiency of Er3+ (Yb3+).
1999, Journal of Nanoparticle Research, 1 (1), 83 - 90[Refereed]
Scientific journal
Carbon onions prepared by high-temperature annealing of nanocrystalline diamonds (nc-D) have been studied by electron energy-loss spectroscopy. It was found that the core-loss spectrum of spherical carbon onions was very similar to that of nc-D, although the low-loss spectrum and the high-resolution transmission electron microscopic observation suggest the formation of graphitic sp2 network. The core-loss spectrum indicates that spherical onions have a number of sp3 bonds. A possible explanation for these sp3 bonds is that there remains a tiny residual diamond particle in a spherical onion. Another explanation is that the spherical carbon onion has sp3 bonds as structural defects.
1999, Chemical Physics Letters, 305 (3-4), 225 - 229[Refereed]
Scientific journal
Photoluminescence (PL) decay dynamics of Ge nanocrystals (nc-Ge) 1.2-3.2 nm in average diameter embedded in SiO2 matrices was studied. The samples showed a PL peak in the near-infrared region with strong size dependence. A very fast component (≪1 μs) was found in decay curves for all the samples. For the samples containing relatively large nc-Ge, a slow component of the order of microseconds was also observed. With decreasing the size, the slow component gradually faded out, and the PL intensity increased significantly. The transition from indirect to direct recombination of carriers with decreasing the size is considered to be responsible for the observed PL decay dynamics. © 1999 American Institute of Physics.
1999, Applied Physics Letters, 74 (11), 1558 - 1560[Refereed]
Scientific journal
- Raman identification of onion-like carbon
A specific Raman spectrum of carbon spherical shells (onions) synthesized by annealing-induced (T=1800 K) chipping off the outer carbon layers from 5-nm size diamond particles has been observed. It shows a clearly seen band at 1572 cm(-1). Its downshift from the position 1582 cm(-1) (known for a pure graphite) is interpreted as an influence of shell curvature. The summary contribution of the shells constituting the 5-nm diameter onion is estimated. A narrowness (FWHM =15 cm(-1)) of the first order Raman band of onions together with a dominance of the peak at 2712 cm(-1) (FWHM=65 cm(-1)) in their second order spectrum point to a high degree of structural perfection of a graphitic network in shells. (C) 1998 Elsevier Science Ltd. All rights reserved.
ELSEVIER SCIENCE BV, 1998, FULLERENES AND CARBON BASED MATERIALS, 68, 821 - 826, English[Refereed]
International conference proceedings
We have succeeded in observing the size dependent photoluminescence (PL) from Ge nanocrystals (nc-Ge) with 0.9-5.3 nm in average diameter (Formula presented) in the near-infrared region. The nc-Ge were fabricated by rf cosputtering of Ge and (Formula presented) and post annealing at (Formula presented) It was found that the sample with (Formula presented) shows a PL peak at about 0.88 eV. With decreasing the size, the PL peak shifted to higher energies and reached 1.54 eV for the sample with (Formula presented) It was also found that the PL intensity increases drastically with decreasing the size. The observed strong size dependence of the PL spectra indicates that the observed PL originates from the recombination of electron-hole pairs confined in nc-Ge. © 1998 The American Physical Society.
1998, Physical Review B - Condensed Matter and Materials Physics, 58 (12), 7921 - 7925[Refereed]
Scientific journal
Current transport properties of thin Ag-SiO2 granular films were studied. In spite of very simple device structures (i.e., just sandwiching the granular film with Al electrodes), clear Coulomb blockade and Coulomb staircase structures were observed in the current-voltage (I-V) characteristics. The observed I-V characteristics were qualitatively explained by a double-barrier and a triple-barrier tunnel-junction model. © 1998 Academic Press Limited.
1998, Superlattices and Microstructures, 23 (1), 173 - 176[Refereed]
Scientific journal
Electrical transport properties of thin SiO2 films containing Ge nanocrystals have been studied. Steplike structures were observed on current-voltage characteristics. The structures changed depending on the size of nanocrystals. The observed step structures could be explained by a model considering the interplay between the resonant tunneling of electrons through the discrete electronic states of Ge nanocrystals and the single electron charging effect of Ge nanocrystals. © 1998 Elsevier Science Ltd. All rights reserved.
1998, Solid-State Electronics, 42 (7-8), 1605 - 1608[Refereed]
Scientific journal
- Raman investigation of onion-like carbon
Combined investigation (Raman scattering, HRTEM and X-ray diffraction techniques) performed for 5 nm-size ultradispersed diamond powder and the products of its annealing in vacuum has revealed the highest percentage of the spherical carbon onions in the powder annealed at T = 1800 K.
GORDON BREACH SCI PUBL LTD, 1998, Molecular Crystals and Liquid Crystals Science and Technology Section C-Molecular Materials, 10 (1-4), 249 - 254, English[Refereed]
Scientific journal
A specific Raman spectrum of carbon spherical shells (onions) synthesized by annealing-induced (T = 1800 K) chipping off the outer carbon layers from 5-nm size diamond particles has been observed. It shows a clearly seen band at 1572 cm-1. Its downshift from the position 1582 cm-1 (known for a pure graphite) is interpreted as an influence of shell curvature. The summary contribution of the shells constituting the 5-nm diameter onion is estimated. A narrowness (FWHM = 15 cm-1) of the first order Raman band of onions together with a dominance of the peak at 2712 cm-1 (FWHM = 65 cm-1) in their second order spectrum point to a high degree of structural perfection of a graphitic network in shells. © 1998 Elsevier Science Ltd. All rights reserved.
1998, Carbon, 36 (5-6), 821 - 826[Refereed]
Scientific journal
SiO2 films containing Si nanocrystals (nc-Si) and Er were prepared and their photoluminescence (PL) properties were studied. The samples exhibited PL peaks at 0.8 and 1.54 μm, which could be assigned to the electron-hole recombination in nc-Si and the intra-4f transition in Er3+ respectively. Correlation between the intensities of the two PL peaks was studied as functions of the size of nc-Si, Er concentration, excitation power and excitation wavelength. It was found that the 1.54 μm PL of Er3+ is strongly enhanced by incorporating nc-Si in films. Furthermore, the intensity of the 1.54 μm peak was found to depend strongly on the size of the incorporated nc-Si. © 1998 American Institute of Physics.
1998, Journal of Applied Physics, 84 (8), 4525 - 4531[Refereed]
Scientific journal
Boron-doped Si nanocrystals as small as 3.5 nm were prepared and their photoluminescence (PL) properties were studied. The PL properties were found to be very sensitive to the B concentration. For the sample without B doping the temperature-dependent shift of the PL peak was almost the same as that of the bulk band gap. As the B concentration increased, the temperature dependence deviated from that of the bulk band gap, and the peak exhibited a low-energy shift as the temperature decreased. The anomalous temperature dependence is considered to be due to the contribution of the PL from excitons bound to the neutral B states. © 1998 American Institute of Physics.
1998, Journal of Applied Physics, 83 (12), 7953 - 7957[Refereed]
Scientific journal
SiO2 films containing Si nanocrystals (nc-Si) and Yb were prepared and their photoluminescence (PL) properties were studied. For the sample containing nc-Si with an average diameter of 3.1 nm, a weak peak (∼1.26eV) attributable to the intra-4f shell transition of Yb3+ could be observed at the low-energy side of a broad peak (∼1.4eV) of nc-Si. The intensity of the 1.26 eV peak was found to depend strongly on the size of nc-Si and increase rapidly with decreasing size. The temperature dependence of the PL spectra was studied. It was found that the degree of temperature quenching of the 1.26 eV peak depends on the size of the nc-Si and becomes small as the size decreases. These results suggest that the band-gap widening of nc-Si due to the quantum size effects is essential to efficiently excite Yb3+ by nc-Si. © 1998 American Institute of Physics.
1998, Applied Physics Letters, 73 (21), 3108 - 3110[Refereed]
Scientific journal
The electrical transport properties of SiO2 films (≥ 3 μm in thickness) containing Ge nanocrystals have been studied. We found that the films exhibit T-1/2 dependence of ln(σ) under relatively low electric fields independent of the volume fraction of Ge in the films, where T and σ are the temperature and the conductivity, respectively. The observed electrical properties could be well explained by the theory developed by Šimánek [Solid State Commun. 40, 1021 (1981)] which considers the tunneling of thermally activated carriers between neighboring nanocrystals. © 1998 American Institute of Physics.
1998, Journal of Applied Physics, 83 (3), 1507 - 1512[Refereed]
Scientific journal
- 1.54 mu m photoluminescence of Er3+ doped into SiO2 films containing Si nanocrystals: Evidence for energy transfer from Si nanocrystals to Er3+
SiO2 films containing Si nanocrystals (nc-Si) and Er were prepared and their photoluminescence (PL) properties were studied, The samples exhibited luminescence peaks at 0.81 and 1.54 mu m, which could be assigned to the electron-hole recombination in nc-Si and the intra-4f transition in Er3+, respectively. Correlation between the intensities of the two luminescence peaks was studied as functions of Er concentration and excitation power, The present results clearly demonstrate that excitation of Er3+ occurs through the recombination of photogenerated carriers spatially confined in nc-Si and the subsequent energy transfer to Er3+. (C) 1997 American Institute of Physics.
AMER INST PHYSICS, Sep. 1997, APPLIED PHYSICS LETTERS, 71 (9), 1198 - 1200, English[Refereed]
Scientific journal
Photoluminescence (PL) spectra of Si nanocrystals embedded in SiO2 films were measured as a function of the size. Samples were prepared by r.f. cosputtering of Si and SiO2 and post-annealing. The average particle sizes for all the samples were directly estimated by high-resolution transmission electron microscopic observations. For each sample, a broad PL peak was observed in the near-infrared region. As the average particle size decreased from 3.8 nm to 2.7 nm, the peak exhibited a blue shift from 1.42 eV to 1.54 eV and its intensity increased progressively. This strong size dependence of the PL peak suggests that the PL peak arises from the recombination of electrons and holes confined in the Si nanocrystals. © 1997 Elsevier Science Ltd.
1997, Solid State Communications, 102 (7), 533 - 537[Refereed]
Scientific journal
Current-transport properties of extremely thin composite films of Ag-SiO2 and Au-SiO2 (about 9 to 15 nm in thickness) were studied. The observation of the sample cross-section by high-resolution transmission electron microscopy revealed that only a few Ag (Au) nanocrystals exist across the films. In spite of the simple device structure (i.e. just sandwiching the granular film between Al electrodes) and very large electrodes (100 μm × 100 μm), Coulomb blockade (CB) and Coulomb staircase (CS) structures have been clearly observed at low temperatures. As the temperature rose, the CB and CS structures smeared out and random telegraph signals due probably to a charge trapped at the interfaces between the nanocrystals and SiO2 matrices were observed.
1997, Journal of Physics Condensed Matter, 9 (41), 8669 - 8677[Refereed]
Scientific journal
SiO2 films containing Si nanocrystals (nc-Si) and Er were prepared and their photoluminescence (PL) properties were studied. The samples exhibited luminescence peaks at 0.81 and 1.54 μm, which could be assigned to the electron-hole recombination in nc-Si and the intra-4f transition in Er3+, respectively. Correlation between the intensities of the two luminescence peaks was studied as functions of Er concentration and excitation power. The present results clearly demonstrate that excitation of Er3+ occurs through the recombination of photogenerated carriers spatially confined in nc-Si and the subsequent energy transfer to Er3+. © 1997 American Institute of Physics.
1997, Applied Physics Letters, 71 (9), 1198 - 1200[Refereed]
Scientific journal
- Raman scattering from acoustic phonons confined in Si nanocrystals
We have observed Raman scattering from acoustic phonons confined in Si nanocrystals. It was found that the Raman spectra depend strongly on the size of the nanocrystals and the peaks shift to higher frequencies as the size decreases. We also found that the depolarized Raman spectra appear at much lower frequencies than the polarized ones.
AMER PHYSICAL SOC, 1996, Physical Review B, 54 (12), R8373 - R8376, English[Refereed]
Scientific journal
We have observed Raman scattering from acoustic phonons confined in Si nanocrystals. It was found that the Raman spectra depend strongly on the size of the nanocrystals and the peaks shift to higher frequencies as the size decreases. We also found that the depolarized Raman spectra appear at much lower frequencies than the polarized ones. © 1996 The American Physical Society.
1996, Physical Review B - Condensed Matter and Materials Physics, 54 (12), R8373 - R8376[Refereed]
Scientific journal
- 1996, Physical Review B, 54 (12), R8373 - R8376
[Refereed]
Scientific journal
We prepared B-doped Si microcrystals using an r.f. cosputtering method. The samples were investigated by transmission electron microscopy, IR absorption and Raman measurements. The Raman spectra of the samples were found to change depending on the excitation wavelength. The asymmetric spectral shapes observed were very similar to those observed for heavily B-doped bulk Si. The characteristic excitation-wavelength dependence of the spectra can be attributed to discrete-continuum Fano-type interference in the Si microcrystals. The IR absorption spectra showed a broad structure which is considered to arise from resonant excitation of surface plasmons in Si microcrystals. These results clearly suggest that B atoms are efficiently incorporated into Si microcrystals.
1996, Materials Science and Engineering A, 217-218, 155 - 158[Refereed]
Scientific journal
Extinction and Raman spectra of gas-evaporated carbon nanoparticles were studied. It was found from Raman spectroscopy that the gas-evaporated carbon nanoparticles consist of small sp2 carbon clusters and the sp2 clusters grow on thermal annealing without affecting the size of the particle itself. The as-deposited samples show an extinction peak at about 230 nm, which exhibits a red shift as the annealing temperature increases. Combining the results of Raman spectroscopy, we conclude that the extinction peak arises from the π-plasmon resonances in sp2 clusters and the resonant frequency decreases as the sp2 clusters grow.
1996, Materials Science and Engineering A, 217-218, 176 - 180[Refereed]
Scientific journal
Temperature dependence of electrical characteristics of SiO2 films doped with C, Si, and Ge were studied. The conductivity σ was found to vary with the temperature as lnσ∝T-1/4 over a wide temperature range, indicative of the conduction by the variable range hopping (VRH) mechanism. Since the previous optical studies for the same films indicate the existence of clusters in the films, it is very likely that the VRH through localized states associated with clusters dominates the conduction process, irrespective of the kind of group IV elements. © 1996 American Institute of Physics.
1996, Applied Physics Letters, 68 (26), 3749 - 3751[Refereed]
Scientific journal
We have succeeded, for the first time, in doping B atoms into Si nanocrystals well dispersed in an oxide matrix. The samples were prepared by cosputtering of Si, SiO2 and B2O3 targets and post-annealing. The growth of Si nanocrystals in the matrix was demonstrated by high-resolution electron microscopy. Raman spectra of the samples exhibited asymmetric line shapes, which showed a strong dependence on the excitation wavelength. The Raman results can be well explained in terms of the Fano-type interference between the phonon scattering and electronic excitations. Since the Fano-type interference is possible only for heavily doped Si crystals, the present Raman results clearly demonstrate the success in B doping into well dispersed Si nanocrystals. Copyright ©\Theta 1996 Elsevier Science Ltd.
1996, Solid State Communications, 100 (4), 227 - 230[Refereed]
Scientific journal
- 1995, Physical Review B, 52 (19), 14273 - 14273
[Refereed]
Scientific journal
- AMERICAN PHYSICAL SOC, 1995, Physical Review B, 52 (19), 14273 - 14273, English
[Refereed]
Scientific journal
- Hopping conduction in SiO
2 films containing C, Si, and Ge clustersTemperature dependence of electrical characteristics of SiO2 films doped with C, Si, and Ge were studied. The conductivity σ was found to vary with the temperature as lnσ∝T-1/4 over a wide temperature range, indicative of the conduction by the variable range hopping (VRH) mechanism. Since the previous optical studies for the same films indicate the existence of clusters in the films, it is very likely that the VRH through localized states associated with clusters dominates the conduction process, irrespective of the kind of group IV elements.© 1996 American Institute of Physics.
1995, Applied Physics Letters, 3749 - 3749[Refereed]
Scientific journal
Infrared absorption in composite films of SiO2 and microcrystalline Ge has been investigated with p- and s-polarized light under 45-degrees oblique incidence. In the case of p-polarized incident light, pure SiO2 films clearly exhibit an absorption peak of the LO-phonon mode around 1240 cm-1 in addition to that of the TO mode at 1080 cm-1, due to the so-called Berreman effect. It was found that the intensity of the LO absorption relative to that of the TO absorption decreases as the volume fraction of Ge microcrystals in the film increases. Theoretical calculations based on the Bruggeman and Maxwell-Garnett effective-medium theories have been performed. The calculations made by the Bruggeman theory could successfully reproduce the observed spectra and well explain the decrease in the intensity of the LO absorption, while those made by the Maxwell-Garnett theory disagreed with the experiments.
AMER PHYSICAL SOC, 1992, Physical Review B, 46 (24), 15930 - 15935, English[Refereed]
Scientific journal
- 1992, Journal of the Physical Society of Japan, 61 (2), 754 - 755
[Refereed]
Scientific journal
Infrared absorption in composite films of SiO2 and microcrystalline Ge has been investigated with p- and s-polarized light under 45°oblique incidence. In the case of p-polarized incident light, pure SiO2 films clearly exhibit an absorption peak of the LO-phonon mode around 1240 cm-1 in addition to that of the TO mode at 1080 cm-1, due to the so-called Berreman effect. It was found that the intensity of the LO absorption relative to that of the TO absorption decreases as the volume fraction of Ge microcrystals in the film increases. Theoretical calculations based on the Bruggeman and Maxwell-Garnett effective-medium theories have been performed. The calculations made by the Bruggeman theory could successfully reproduce the observed spectra and well explain the decrease in the intensity of the LO absorption, while those made by the Maxwell-Garnett theory disagreed with the experiments. © 1992 The American Physical Society.
1992, Physical Review B, 46 (24), 15930 - 15935[Refereed]
Scientific journal
Intense, low-frequency Raman scattering from localized acoustic vibrations of small, spherical Ag particles embedded in SiO2 thin films has been observed. It was found that the Raman peak shifts to higher frequencies as the particle size decreases. For Ag particles smaller than 4 nm, the size dependence of the peak frequency can be well explained by Lambs theory, which gives vibrational frequencies of a homogeneous elastic body with a spherical form. The Raman scattering observed is relatively strong and believed to be enhanced by the excitation of the surface plasmons localized in the Ag particles; the enhancement mechanism is analogous to the case of surface-enhanced Raman scattering from molecules adsorbed on rough metal surfaces. © 1991 The American Physical Society.
1991, Physical Review B, 44 (12), 6243 - 6248[Refereed]
Scientific journal
Intense, low-frequency Raman scattering from localized acoustic vibrations of small, spherical Ag particles embedded in SiO2 thin films has been observed. It was found that the Raman peak shifts to higher frequencies as the particle size decreases. For Ag particles smaller than 4 nm, the size dependence of the peak frequency can be well explained by Lamb's theory, which gives vibrational frequencies of a homogeneous elastic body with a spherical form. The Raman scattering observed is relatively strong and believed to be enhanced by the excitation of the surface plasmons localized in the Ag particles; the enhancement mechanism is analogous to the case of surface-enhanced Raman scattering from molecules adsorbed on rough metal surfaces.
AMERICAN PHYSICAL SOC, 1991, Physical Review B, 44 (12), 6243 - 6248, English[Refereed]
Scientific journal
The growth of Ge microcrystals in Si02-Ge mixture films prepared by an rf co-sputtering method was studied by Raman spectroscopy and electron microscopy. It was found that in the as-deposited films, Ge clusters about 2 nm in diameter are embedded in Si02 matrices and they are grown to Ge microcrystals by thermal annealing. It is shown that annealing at 800°C is necessary to prepare well-grown microcrystalline samples. The microcrystalline size dependence of the Raman spectrum was investigated. The increase in the linewidth observed with decreasing the size can be well explained by the phonon confinement theory, while the downward shift of the peak frequency predicted from the theory was not observed, presumably due to the stress caused by Si02 matrices. © 1991 The Japan Society of Applied Physics.
1991, Japanese Journal of Applied Physics, 30 (4), 687 - 694[Refereed]
Scientific journal
Optical extinction spectra of gas-evaporated Ag small particles have been investigated. It is shown that the extinction spectra exhibit a long tail at the long-wavelength side of the surface plasmon resonance. From a comparison of spectra obtained for samples having different degrees of particle aggregation, it is concluded that the tail is caused by the particle aggregation. Theoretical calculations based on the effective medium theory support this conclusion. Enhanced Raman scattering previously observed for the same type of samples can be well explained in terms of the surface plasmon resonance at the tail region. © 1990.
1990, Solid State Communications, 76 (8), 1067 - 1070[Refereed]
Scientific journal
Surface oxide layers formed on gas-evaporated Si and Ge microcrystals as small as 100Å were investigated by means of infrared spectroscopy, high-resolution electron microscopy and X-ray photoemission spectroscopy. It is shown that 20Å-thick native oxide layers in the form of SiOx with x=∼1.2 are first formed on the surfaces of Si microcrystals. When the microcrystals are annealed in air at 400°C, the composition x increases up to 2, but the oxide thickness remains almost the same. The evolution of the oxide occurs in the first 15min of annealing and saturates afterwards. This implies that stable oxide layers (SiO2) can successfully be obtained by annealing at relatively low temperatures. Results obtained for Ge microcrystals are qualitatively the same and indicate that stable oxide coatings can be obtained by annealing at 300°C for 30min. © 1990.
1990, Superlattices and Microstructures, 8 (1), 13 - 18[Refereed]
Scientific journal
Raman measurements were carried out on Ge quantum dots from 6.1 to 15 nm in size embedded in SiO2 thin films. The samples were prepared by rf co-sputtering and post- annealing. In contrast to the amorphous-like broad spectra previously obtained for gas- evaporated Ge microcrystals of comparable sizes, relatively sharp lines around 300 cm-1 were observed, because the present dots satisfy the fixed boundary condition. The increase in the linewidth observed with decreasing the size is in good agreement with the results of the calculation based on the phonon confinement model. However, the downward shift of the line predicted from the calculation was not observed presumably due to the compressive stress exerted on the dots.
1990, Applied Physics Letters, 57 (25), 2692 - 2694[Refereed]
Scientific journal
- WORLD SCIENTIFIC PUBL CO PTE LTD, 1990, 20th International Conference on the Physics of Semiconductors, Vols 1-3, 2375 - 2378, EnglishQUANTUM DOTS OF GE EMBEDDED IN SIO2 THIN-FILMS - OPTICAL-PROPERTIES
[Refereed]
Scientific journal
By applying an rf co-sputtering technique, we have succeeded in producing Ge microcrystals in SiO2thin films for which direct characterization by transmission electron microscopy is possible. As the size of the Ge microcrystals decreased from 6.5 to 2.7 nm, the optical extinction (absorption) spectra changed drastically. The structures corresponding to interband transitions in bulk Ge disappeared, and the onset of extinction shifted to higher energies. These spectral changes seem to arise from the three-dimensional confinement of electrons and holes in the microcrystals. © 1989 The Japan Society of Applied Physics..
1989, Japanese Journal of Applied Physics, 28 (8 A), L1464 - L1466[Refereed]
Scientific journal
- JAPAN SOC APPLIED PHYSICS, 1989, Japanese Journal of Applied Physics Part 2-Letters, 28 (8), L1464 - L1466, EnglishQUANTUM SIZE EFFECTS IN GE MICROCRYSTALS EMBEDDED IN SIO2 THIN-FILMS
[Refereed]
Scientific journal
SiGe alloy films prepared by rf sputtering have been investigated by Raman spectroscopy and high-resolution electron microscopy. As-deposited films and films annealed at 600ºC show broad Raman spectra usually attributed to continuous random network structures (amorphous). Electron diffraction patterns of the films are diffuse halos. However, high-resolution TEM images clearly show lattice fringes corresponding to microcrystals about 2 nm in size. The observed broad Raman spectra do not imply the continuous random structure of the films. © 1988 The Japan Society of Applied Physics.
1988, Japanese Journal of Applied Physics, 27 (7A), L1165 - L1167[Refereed]
Scientific journal
MISC
- Jul. 2016, SPIE Newsroom, English
[Refereed]
Report scientific journal
- The Institute of Electronics, Information and Communication Engineers, 24 Feb. 2015, Proceedings of the IEICE General Conference, 2015 (1), "SS - 13"-"SS-14", JapaneseCI-1-3 Luminescence properties of colloidal silicon nanocrystals
- IOP PUBLISHING LTD, 2014, Nanotechnology, 25 (45), English
[Refereed]
- Nonlinear optical responses of impurities-doped silicon nanocrystals : Enhancement of the nonlinear optical responses by Bi doping
Recently, nonlinear optical responses of silicon nanocrsytals (Si-ncs) have attracted much attention. Due to the quantum and surface effects, Si-ncs show nonlinear optical responses which are several orders of magnitudes larger than those of bulk Si. In addition, the nonlinear optical response is ultrafast and of the order of femtoseconds. Our laboratory has been investigating the linear and nonlinear optical response of impurities doped Si-ncs. We demonstrated that the nonlinear response of Si-ncs can be enhanced by several times by doping a small amount of phosphorus and/or boron atoms into Si-ncs. In this work, we focus on bismuth (Bi) as an impurity atom and demonstrate that Bi-doping can significantly improve the nonlinear optical properties of Si-ncs.
The Institute of Electronics, Information and Communication Engineers, 21 Dec. 2012, Technical report of IEICE. OPE, 112 (371), 33 - 37, Japanese - The Physical Society of Japan (JPS), 24 Aug. 2012, Meeting abstracts of the Physical Society of Japan, 67 (2), 707 - 707, Japanese20pFJ-7 Ge composition dependence of multiple exciton generation in Si_<1-x>Ge_x nanocrystals
- ニューガラスフォーラム, Jun. 2012, New glass, 27 (2), 33 - 35, JapaneseEnhancement of up-conversion photo-luminescence by localized surface plasmons in metal nano particles
- The Physical Society of Japan (JPS), 05 Mar. 2012, Meeting abstracts of the Physical Society of Japan, 67 (1), 826 - 826, Japanese27pBL-6 Quantized Auger Recombination in Si_(1-x)Ge_x Nanocryetale
- 大阪大学超高圧電子顕微鏡センター, 2012, 大阪大学超高圧電子顕微鏡センター年報, (41), 22 - 24, JapaneseSi nanocrystals dispersible in polar liquids without functionalization by organic molecules
- Ultraviolet true-zero order wave plate made of porous silica
Porous silicon made from (110) Si wafers exhibits strong in-plane optical anisotropy (birefringence). Oxidation of the birefringent porous silicon results in the formation of birefringent porous silica. We demonstrate that the degree of the birefringence of porous silica can be controlled by the oxidation condition and very small birefringence can be achieved. The smallest anisotropy of the refractive index (Δn) is 0.001. The small birefringence allows us to produce true zero-order wave plates operating in the deep ultraviolet range.
The Institute of Electronics, Information and Communication Engineers, 09 Dec. 2011, Technical report of IEICE. OPE, 111 (358), 7 - 11, Japanese - The Physical Society of Japan (JPS), 03 Mar. 2011, Meeting abstracts of the Physical Society of Japan, 66 (1), 741 - 741, Japanese25pHB-5 Auger Recombination Dynamics in Si_<1-x>Ge_x Nanocrystals
- Jul. 2010, 神戸大学連携推進本部先端研究推進部門2009年度年報, Vol. 5 (2009),p. 103, Japanese石英系光導波路素子の開発
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- Aug. 2009, 神戸大学連携推進本部先端研究推進部門2008年度年報, Vol. 4 (2009),p. 99, Japanese石英系光導波路素子の開発
Others
- The Physical Society of Japan (JPS), 29 Feb. 2008, Meeting abstracts of the Physical Society of Japan, 63 (1), 169 - 169, Japanese24aYG-4 Resonant photon tunnelling experiments on alternating metal / dielectric multilayer metamaterials
- Oct. 2006, 神戸大学連携推進本部先端研究推進部門2005年度年報, Vol.1,pp82-83, Japanese光導波路アンプ開発
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- The Physical Society of Japan (JPS), 18 Aug. 2006, Meeting abstracts of the Physical Society of Japan, 61 (2), 105 - 105, Japanese24pWB-14 Enhancement of upconversion luminescence of Er^<3+> ions near a thin metal film
- The Physical Society of Japan (JPS), 18 Aug. 2006, Meeting abstracts of the Physical Society of Japan, 61 (2), 596 - 596, Japanese24pWB-14 Enhancement of upconversion luminescence of Er^<3+> ions near a thin metal film
- The Physical Society of Japan (JPS), 18 Aug. 2006, Meeting abstracts of the Physical Society of Japan, 61 (2), 582 - 582, Japanese24aRA-9 Photoluminescence quantum efficiency of Si nanocrystals
- The Physical Society of Japan (JPS), 04 Mar. 2006, Meeting abstracts of the Physical Society of Japan, 61 (1), 738 - 738, Japanese28aPS-60 Spectroscopic ellipsometry of noble-metal nanocomposite films
- Application of Si・Er-codoped SiO_2 films to optical waveguide amplifiers
Waveguide propagation losses (λ : 1.55μm) in Si nanocrystals and Er codoped SiO_2 films were measured with various doping concentrations for an application to a waveguide amplifier. Photoluminescence intensity by Er ions was measured to be higher by increasing the Si concentration, and lower by increasing it further. Without excitation to a waveguide, the waveguide loss was increased by increased by increasing the Si concentration. It is important that the Si nanocrystals should be evaluated as a cause of a loss as well as a sensitizer for the amplifier. Propagation losses were also measured by changing both the Er and Si concentrations. It is important to optimize both the Si and Er concentrations, based on the results of those loss values.
The Institute of Electronics, Information and Communication Engineers, 25 Jan. 2006, Technical report of IEICE. LQE, 105 (592), 73 - 76, Japanese - Application of Si・Er-codoped SiO_2 films to optical waveguide amplifiers
Waveguide propagation losses (λ : 1.55μm) in Si nanocrystals and Er codoped SiO_2 films were measured with various doping concentrations for an application to a waveguide amplifier. Photoluminescence intensity by Er ions was measured to be higher by increasing the Si concentration, and lower by increasing it further. Without excitation to a waveguide, the waveguide loss was increased by increased by increasing the Si concentration. It is important that the Si nanocrystals should be evaluated as a cause of a loss as well as a sensitizer for the amplifier. Propagation losses were also measured by changing both the Er and Si concentrations. It is important to optimize both the Si and Er concentrations, based on the results of those loss values.
The Institute of Electronics, Information and Communication Engineers, 25 Jan. 2006, Technical report of IEICE. OFT, 105 (586), 73 - 76, Japanese - Application of Si・Er-codoped SiO_2 films to optical waveguide amplifiers
Waveguide propagation losses (λ : 1.55μm) in Si nanocrystals and Er codoped SiO_2 films were measured with various doping concentrations for an application to a waveguide amplifier. Photoluminescence intensity by Er ions was measured to be higher by increasing the Si concentration, and lower by increasing it further. Without excitation to a waveguide, the waveguide loss was increased by increased by increasing the Si concentration. It is important that the Si nanocrystals should be evaluated as a cause of a loss as well as a sensitizer for the amplifier. Propagation losses were also measured by changing both the Er and Si concentrations. It is important to optimize both the Si and Er concentrations, based on the results of those loss values.
The Institute of Electronics, Information and Communication Engineers, 25 Jan. 2006, Technical report of IEICE. OPE, 105 (589), 73 - 76, Japanese - Application of Si・Er-codoped SiO_2 films to optical waveguide amplifiers
Waveguide propagation losses (λ : 1.55μm) in Si nanocrystals and Er codoped SiO_2 films were measured with various doping concentrations for an application to a waveguide amplifier. Photoluminescence intensity by Er ions was measured to be higher by increasing the Si concentration, and lower by increasing it further. Without excitation to a waveguide, the waveguide loss was increased by increased by increasing the Si concentration. It is important that the Si nanocrystals should be evaluated as a cause of a loss as well as a sensitizer for the amplifier. Propagation losses were also measured by changing both the Er and Si concentrations. It is important to optimize both the Si and Er concentrations, based on the results of those loss values.
The Institute of Electronics, Information and Communication Engineers, 25 Jan. 2006, IEICE technical report, 105 (583), 73 - 76, Japanese - Oct. 2005, 神戸大学ベンチャー・ビジネス・ラボラトリー年報2005, Vol.10, pp20-25, Japanese光導波路アンプ開発
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The photoluminescence (PL) spectra and kinetics of erbium-doped layers of silicon nanocrystals dispersed in a silicon dioxide matrix (nc-Si/SiO 2) are studied. It was found that optical excitation of nc-Si can be transferred with a high efficiency to Er3+ ions present in the surrounding oxide. The efficiency of energy transfer increases with increasing pumping photon energy and intensity. The process of Er3+ excitation is shown to compete successfully with nonradiative recombination in the nc-Si/SiO2 structures. The Er3+ PL lifetime was found to decrease under intense optical pumping, which implies the establishment of inverse population in the Er3+ system. The results obtained demonstrate the very high potential of erbium-doped nc-Si/SiO2 structures when used as active media for optical amplifiers and light-emitting devices operating at a wavelength of 1.5 μm. © 2005 Pleiades Publishing, Inc.
2005, Physics of the Solid State, 47 (1), 121 - 124, English[Refereed]
- Dec. 2004, 神戸大学ベンチャー・ビジネス・ラボラトリー年報2004, Vol.9,70-77, Japanese光導波路アンプ開発
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- 13 May 2004, 希土類 = Rare earths, 44, 122 - 123, JapanesePhoto-sensitization of Er ions by Si nanocrystal in SiO_2
It is known that carbonaceous dust in interstellar space shows a strong extinction bump at 217.5 nm (4.6 μm-1, 5.7 eV). One of the possible candidates for such carbonaceous interstellar dusts is a new member of the fullerene family called the carbon onion. Recently, we conducted a laboratory experiment to study the optical extinction properties of carbon onions. In order to explain the experimental results, a new dielectric model of the onions, the "defective" spherical onion model, was proposed. Here we show that the defective carbon onions are likely to be one of the origins of the interstellar extinction bump. This report also suggests that carbonaceous interstellar dust particles may be replicated by onions produced in the laboratory.
2004, Astrophysical Journal, 609 (1 I), 220 - 224, English[Refereed]
The use of porous Si as a photosensitizer in singlet oxygen formation in solution was investigated. 1,3-diphenylisobenzofuran (DPBF) was used as a singlet oxygen acceptor. A double-beam spectrophotometer was used in the study. It was observed that a molecule-like electronic structure of excitons in Si nanocrystals was essential in realizing a function as a photosensitizer. With fresh porous Si dispersed in the solution, the absorption band of DPBF was found to decrease by irradiation with green or red light.
2004, Journal of Applied Physics, 95 (7), 3689 - 3693, English[Refereed]
The study of ferromagnetic resonance (FMR) in diluted Fe nanogranular films with small values for the Fe volume fraction (v) was carried out. It was observed that the uniform mode signal of the v=5% film was not affected by either the angle or the temperature of the film. The uniform mode signal of the v=15% film was observed to be strongly dependent on the angle and the temperature of the film. It was found that the resonance of the FMR uniform mode was strongly affected by the temperature, the v and the angle between the film plane and the applied magnetic field.
2004, Journal of Applied Physics, 95 (12), 8194 - 8198, English[Refereed]
We report on the mechanism of photodegradation of porous silicon luminescence in ambient containing molecular oxygen. Energy transfer from excitons confined in silicon nanocrystallites to molecular oxygen results in the generation of highly chemically reactive singlet oxygen molecules. The subsequent interaction of singlet oxygen molecules with the hydrogenated surface of silicon nanocrystals results in its photooxidation and the creation of additional nonradiative defects, i.e., the luminescence fatigue effect. © 2004 American Institute of Physics.
2004, Applied Physics Letters, 85 (16), 3590 - 3592, English[Refereed]
Photoluminescence (PL) from singlet oxygen generated by energy transfer from porous Si is observed at room temperature in an organic solvent. The evidence of the indirect excitation by energy transfer is obtained from PL excitation spectroscopy. The excitation spectrum indicates that by using porous Si as a photosensitizer, light of the entire visible range can be utilized for singlet oxygen generation at room temperature.
AMERICAN PHYSICAL SOC, 2004, Physical Review B, 70 (8), English[Refereed]
The study of the effects of B and P codpoing on photoluminescence (PL) properties of Si nanocrystals (nc-Si) was presented. The PL intensity of codoped nc-Si was shown to be higher than that of either P- or B-doped nc-Si. It was observed that the PL intensity was sometimes even higher that that of pure nc-Si at relatively low P and B concentrations and low annealing temperatures. It was found that the PL peak shifts below the band gap of bulk Si, by doping P and B simultaneously to very high concentrations.
2004, Applied Physics Letters, 85 (7), 1158 - 1160, English[Refereed]
Laser ablation of diamond nanoparticles suspended in ethanol has been performed by using the second harmonic of a Nd:YAG laser (532 nm). UV-Vis absorption spectra revealed the formation of polyynes (C nH 2: n = 8, 10, 12, 14, and 16). The same experiment was performed for graphitic nanoparticles suspended in ethanol. It was found that ablation of diamond nanoparticles results in larger amounts of long polyynes. © 2004 Elsevier B.V. All rights reserved.
2004, Chemical Physics Letters, 395 (1-3), 138 - 142, English[Refereed]
- Nov. 2003, 神戸大学ベンチャー・ビジネス・ラボラトリー年報2003, Vol.8,75-81, Japanese光導波路アンプ開発
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- 01 Sep. 2003, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 27, 454 - 454, JapaneseFerromagnetic resonance in diluted ferromagnetic-metal nanocomposite films
- The Physical Society of Japan (JPS), 15 Aug. 2003, Meeting abstracts of the Physical Society of Japan, 58 (2), 394 - 394, JapaneseFerromagnetic resonance in diluted iron nanocomposite films
- ナノ学会, Mar. 2003, ナノ学会会報, 1 (2), 61 - 66, Japaneseマイクロキャビティー中のSi1-XGeX混晶ナノ結晶からの発光
- 2003, 神戸大学ベンチャー・ビジネス・ラボラトリー年報, 8,49-54, Japanese電子放射によるⅢ-Ⅴ族化合物の化学的および幾何学的不規則化
Others
- 2003, 神戸大学ベンチャー・ビジネス・ラボラトリー年報2003, 8,82-87, Japanese光増感剤としてのSiナノ結晶
Others
- 2003, 神戸大学ベンチャー・ビジネス・ラボラトリー年報2003, 8,130-133, JapaneseIV属混晶半導体ナノ結晶の光物性に関する研究
Others
- The Physical Society of Japan (JPS), 03 Sep. 2001, Meeting abstracts of the Physical Society of Japan, 56 (2), 597 - 597, JapanesePhotoluminescence from Si nanocrystals in Si/SiO_2 microcavity
- The Physical Society of Japan (JPS), 03 Sep. 2001, Meeting abstracts of the Physical Society of Japan, 56 (2), 596 - 596, JapaneseAbsorption spectroscopy of carbon onions prepared by annealing diamond nanoparticle
- 01 Sep. 2001, 日本応用磁気学会学術講演概要集 = Digest of ... annual conference on magnetics in Japan, 25, 261 - 261, JapaneseMagnetic properties of Ni_<1-x>Co_x-C nanogranular thin films prepared by co-sputtering method
- The Physical Society of Japan (JPS), 09 Mar. 2001, Meeting abstracts of the Physical Society of Japan, 56 (1), 358 - 358, JapaneseMagnetic properties of CoNi-C nanogranular thin films
- Kobe University, Mar. 2001, Memoirs of the Graduate School of Science and Technology, Kobe University. A, 19, 97 - 103, EnglishCurrent Fluctuation Induced by Visible Light Irradiation on Single-electron Tunneling via Ge Nanocrystals
- The Physical Society of Japan (JPS), 10 Sep. 2000, Meeting abstracts of the Physical Society of Japan, 55 (2), 692 - 692, JapaneseSynthesis and characterization of carbon onion thin films
- The Physical Society of Japan (JPS), 10 Sep. 2000, Meeting abstracts of the Physical Society of Japan, 55 (2), 691 - 691, JapaneseStructural studies of carbon onions by synchrotron X-ray diffraction
- The Physical Society of Japan (JPS), 10 Sep. 2000, Meeting abstracts of the Physical Society of Japan, 55 (2), 582 - 582, JapanesePhotoluminescence and ESR study of SiGe alloy nanocrystals
- 応用物理学会, 10 Jul. 2000, 應用物理, 69 (7), 820 - 824, JapaneseImpurity doping into Si nanocrystals
- The Physical Society of Japan (JPS), 10 Mar. 2000, Meeting abstracts of the Physical Society of Japan, 55 (1), 717 - 717, JapaneseESR Study of Carbon Onions
- The Physical Society of Japan (JPS), 10 Mar. 2000, Meeting abstracts of the Physical Society of Japan, 55 (1), 741 - 741, JapaneseSynthesis and formation mechanism of filled carbon nanocapsuules
- The Physical Society of Japan (JPS), 10 Mar. 2000, Meeting abstracts of the Physical Society of Japan, 55 (1), 797 - 797, JapaneseGrowth and infrared absorption of SiO_2 nanowires
- 2000, 信学技報, OME 200-99, 1 - 6Au超微粒子を埋め込んだナイロン11蒸着膜の構造と物性
- Photoluminescence from Ge-doped Si nanocrystals
Photoluminescence (PL) properties of SiGe alloy nanocrystals (nc-Si_<1-x>Ge_x) as small as 4-5nm in diameter were studied as a function of Ge contents(x). For the sample with x=0 (pure Si nanocrystals), a PL peak was observed at around 1.45eV ; the peak was assigned to the radiative recombination of electron-hole pairs confined in Si nanocrystals. It was found that the PL peak shifts to lower energies as the Ge content(x) increases. The obserbed peak energy located in between that of Si nanocrystals and Ge nanocrystals previously reported.
The Institute of Electronics, Information and Communication Engineers, 09 Dec. 1999, Technical report of IEICE. SDM, 99 (491), 1 - 6, Japanese - The Physical Society of Japan (JPS), 03 Sep. 1999, Meeting abstracts of the Physical Society of Japan, 54 (2), 839 - 839, Japanese27aZ-8 Low frequency Raman scattering from metal nanocrystals embedded in transparent thin films : excitation wavelength dependence
- The Physical Society of Japan (JPS), 03 Sep. 1999, Meeting abstracts of the Physical Society of Japan, 54 (2), 839 - 839, Japanese27aZ-9 Photocurrent in Al_2O_3 films containing Ag nanocrystale
- The Physical Society of Japan (JPS), 03 Sep. 1999, Meeting abstracts of the Physical Society of Japan, 54 (2), 621 - 621, Japanese27pC-4 Photoluminescence from SiGe alloy nanocrystals
- The Physical Society of Japan (JPS), 03 Sep. 1999, Meeting abstracts of the Physical Society of Japan, 54 (2), 621 - 621, Japanese27pC-5 X-band ESR measurement of P-doped Si nanocrystal
- The Physical Society of Japan (JPS), 03 Sep. 1999, Meeting abstracts of the Physical Society of Japan, 54 (2), 773 - 773, Japanese27pE-4 Transformation of carbon onions into diamond by heat-treerment in an oxidizing environment
- The Physical Society of Japan (JPS), 03 Sep. 1999, Meeting abstracts of the Physical Society of Japan, 54 (2), 730 - 730, Japanese24aF-7 Synthesis of filled carbon nanocapsules by heat treatment of diamond nanoparticles and metals
- Single electron tunneling of SiO_2 films containing Si nanocrystals
Electrical transport properties of extremely thin SiO_2 films(〜8nm)containing Si nanocrystals smaller than 2nm in diameter were studied. Coulomb staircases with a step width of about 250mV were observed at low temperatures. Although the Coulomb staircases were smeared out at room temperature, Coulomb blockade was observed even at room temperature.
The Institute of Electronics, Information and Communication Engineers, 10 Dec. 1998, Technical report of IEICE. SDM, 98 (445), 71 - 74, Japanese - The Physical Society of Japan (JPS), 05 Sep. 1998, Meeting abstracts of the Physical Society of Japan, 53 (2), 159 - 159, JapanesePhotoluminescence of rare-earth ion by the energy transfer from Si nanocrystals
- The Physical Society of Japan (JPS), 05 Sep. 1998, Meeting abstracts of the Physical Society of Japan, 53 (2), 159 - 159, JapanesePhotoluminescence from Si Nanocrystals Doped with B or P Atoms III
- The Physical Society of Japan (JPS), 05 Sep. 1998, Meeting abstracts of the Physical Society of Japan, 53 (2), 292 - 292, JapaneseEELS Study of Onion-Like Carbon Produced from Nanocrystalline Diamond
- The Physical Society of Japan (JPS), 10 Mar. 1998, Meeting abstracts of the Physical Society of Japan, 53 (1), 139 - 139, JapanesePhotoluminescence from Er^<3+> excited by the energy transfer from Si and Ge nanocrystals
- The Physical Society of Japan (JPS), 10 Mar. 1998, Meeting abstracts of the Physical Society of Japan, 53 (1), 139 - 139, JapanesePhotoluminescece of Si Nanocrystals Doped with B or P Atoms
- The Physical Society of Japan (JPS), 16 Sep. 1997, Meeting abstracts of the Physical Society of Japan, 52 (2), 192 - 192, Japanese8p-E-4 Photoluminescence of Si Nanocrystals Doped with B or P Atoms
- The Physical Society of Japan (JPS), 16 Sep. 1997, Meeting abstracts of the Physical Society of Japan, 52 (2), 301 - 301, Japanese8a-D-1 Raman Scattering from Onion-Like Carbon Formed by High Temperature Thermal Annealing
- The Physical Society of Japan (JPS), 17 Mar. 1997, Meeting abstracts of the Physical Society of Japan, 52 (1), 346 - 346, Japanese29p-F-2 Single Electron Transport via Ge Nanocrystal
- The Physical Society of Japan (JPS), 17 Mar. 1997, Meeting abstracts of the Physical Society of Japan, 52 (1), 186 - 186, Japanese28a-YE-3 Near-Infrared Photoluminescence from Ge Nanocrystals
- The Physical Society of Japan (JPS), 17 Mar. 1997, Meeting abstracts of the Physical Society of Japan, 52 (1), 186 - 186, Japanese28a-YE-2 Photoluminescence of Er doped into Si-rich SiO_2 films
- Photoluminescence of Er doped Si-rich SiO2 films
We have prepared SiO_2 films containing Si nanocrystals and h by cosputtering Si,SiO_2 and Er_2O_3. These samples showed photo luminescence (PL) peaks at 1.54eV and 0.81eV which can be attributed to electron-hole recombination in Si nanocrystals and intra-4f transition in Er^<3+>, respectively. As the concentration of Er atoms in the films increased, the PL intensity of Si nanocrystals decreased and that of Er increased. This suggests that the PL of Er is mediated by energy transfer from Si nanocrystals to Er^<3+>
The Institute of Electronics, Information and Communication Engineers, 05 Dec. 1996, Technical report of IEICE. SDM, 96 (395), 27 - 31, Japanese - Near-Infrared Photoluminescence from Si Nanocrystals
Photoluminescence (PL) from Si nanocrystals(2.7-5.5nm) embedded in Si0_2 thin films was stud-led. It was found that Si nanocrystals as small as 3-4nm in diameter exhibit a peak in the near infrared region (1.4-1.5eV). As the size decreased, the PL peak shifted to higher energies and its intensity increased. The temperature dependence of the peak energy was found to be very similar to that of the bulk Si crystal. These suggest that the PL peak arises from the recombination of electrons and holes in Si nanocrystals. At low temperature (<150K), another peak probably associated with the defects at Si-SiO_2 interface was observed at about 0.9eV.
The Institute of Electronics, Information and Communication Engineers, 05 Dec. 1996, Technical report of IEICE. SDM, 96 (395), 1 - 7, Japanese - The Physical Society of Japan (JPS), 13 Sep. 1996, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1996 (2), 339 - 339, JapaneseNear-Infrared Photoluminescence from Si Nanocrystals : Temperature dependence of PL Spectra
- The Physical Society of Japan (JPS), 13 Sep. 1996, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1996 (2), 211 - 211, JapaneseElectrical transport via Si nanocrystals dispersed in SiO_2 thin films
- The Physical Society of Japan (JPS), 13 Sep. 1996, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1996 (2), 631 - 631, JapaneseRaman scattering from onion-like carbon
- The Physical Society of Japan (JPS), 13 Sep. 1996, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1996 (2), 562 - 562, JapaneseRaman and electron microscopic study of carbyne prepared by arc discharge
- The Physical Society of Japan (JPS), 15 Mar. 1996, Abstracts of the meeting of the Physical Society of Japan. Annual meeting, 51 (2), 152 - 152, Japanese1a-F-4 Current transport via Si and Ge nanocrystals dispersed in SiO_2 thin films
- The Physical Society of Japan (JPS), 15 Mar. 1996, Abstracts of the meeting of the Physical Society of Japan. Annual meeting, 51 (2), 519 - 519, Japanese1a-J-6 Electrical - transport properties in thin granular Ag-SiO_2 films
- The Physical Society of Japan (JPS), 15 Mar. 1996, Abstracts of the meeting of the Physical Society of Japan. Annual meeting, 51 (2), 269 - 269, Japanese1p-Y-11 Visible Light Emission from Si-rich SiO2 Films : Effect of High Temperature Annealing
- Characterization of B-doped Si Nanocrystals by Raman and Infrared Absorption Spectroscopy
We have prepared B-doped Si nanocrystals by cosputtering of Si, SiO_2 and B_2O_3. The Raman spectra of the samples were found to change depending on the excitation wavelength. The characteristic excitation-wavelength dependence of the spectra can be attributed to discrete-continuum Fano-type interaction between electronic excitations and phonon scattering in Si nanocrystals. In the infrared absorption spectra, we also observed a peak which is considered to arise from the resonant excitation of surface plasmons in Si nanocrystals. These results clearly suggest that B atoms are efficiently incorporated into Si nanocrystals.
The Institute of Electronics, Information and Communication Engineers, 08 Dec. 1995, Technical report of IEICE. SDM, 95 (400), 17 - 23, Japanese - The Physical Society of Japan (JPS), 12 Sep. 1995, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1995 (2), 491 - 491, Japanese29p-PSB-7 Optical Properties of SiC Fine Particels Embedded in SiO_2 Matrices
- The Physical Society of Japan (JPS), 12 Sep. 1995, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1995 (2), 490 - 490, Japanese29p-PSB-3 Optical Properties of Gas-Evaporated Carbon Nanoparticles
- The Physical Society of Japan (JPS), 12 Sep. 1995, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1995 (2), 235 - 235, Japanese27a-Z-10 Resonant Raman Scattering of Mesoscopic Particles of Group IV Elements Embedded in SiO_2 Matrices
- The Physical Society of Japan (JPS), 12 Sep. 1995, Abstracts of the meeting of the Physical Society of Japan. Sectional meeting, 1995 (2), 156 - 156, Japanese28p-YA-1 Preparation and Raman Spectra of Impurity-doped Si Microcrystals
- The Physical Society of Japan (JPS), 12 Mar. 1992, 年会講演予稿集, 47 (2), 226 - 226, Japanese27a-F-1 Photoluminescence Spectra of SiO_2-Ge Composite Films
- The Physical Society of Japan (JPS), 12 Mar. 1992, 年会講演予稿集, 47 (2), 227 - 227, Japanese27a-F-3 Photoluminescence Spectra from CdS_XSe_<1-X> Microcrystals Embedded in SiO_2 Matrices
- The Physical Society of Japan (JPS), 12 Mar. 1992, 年会講演予稿集, 47 (2), 227 - 227, Japanese27a-F-2 Surface-Enhanced Raman Scattering from SiO_2-Ag Composite Films
- The Physical Society of Japan (JPS), 12 Sep. 1991, 年会講演予稿集, 46 (2), 249 - 249, Japanese29p-H-5 Low-frequency Raman Scattering from Microcrystals
- The Physical Society of Japan (JPS), 12 Sep. 1991, 年会講演予稿集, 46 (2), 247 - 247, Japanese29p-H-1 Raman Scattering from Ge Microcrystals Embedded in Al_2O_3 Marix II
- The Physical Society of Japan (JPS), 12 Sep. 1991, 年会講演予稿集, 46 (2), 247 - 247, Japanese29p-H-2 Raman Scattering from CdS and CdSe Microcrystals Embedded in SiO_2 Matrices
- The Physical Society of Japan (JPS), 11 Mar. 1991, 春の分科会講演予稿集, 1991 (2), 192 - 192, Japanese24a-W-4 Infrared Absorption of SiO_2-Ge Composite Films
- The Physical Society of Japan (JPS), 11 Mar. 1991, 春の分科会講演予稿集, 1991 (2), 196 - 196, Japanese24a-W-12 Low-frequency Raman Scattering from Ag Microcrystals
- The Physical Society of Japan (JPS), 12 Sep. 1990, 秋の分科会講演予稿集, 1990 (2), 433 - 433, Japanese4a-PS-1 Ge Microcrystals in Solid Matrices : Effects of Matrices
- The Physical Society of Japan (JPS), 12 Sep. 1990, 秋の分科会講演予稿集, 1990 (2), 434 - 434, Japanese4a-PS-3 Infrared Absorption of SiO_2-Ge Composit Films
- The Physical Society of Japan (JPS), 16 Mar. 1990, 年会講演予稿集, 45 (2), 396 - 396, JapaneseRaman Scattering from Ge Microcrystals Embedded in SiO2 Thin Films
- The Physical Society of Japan (JPS), 12 Sep. 1989, 秋の分科会講演予稿集, 1989 (2), 377 - 377, Japanese3p-S-11 Optical Absorption of Ag Microcrystals : Effects of Aggregation
- The Physical Society of Japan (JPS), 28 Mar. 1989, 年会講演予稿集, 44 (2), 378 - 378, Japanese29a-TG-6 Optical Properties of Ge Microcrystals Embedded in SiO_2 Matrix
- 一般社団法人日本物理学会, 16 Sep. 1988, 秋の分科会講演予稿集, 1988 (2), 395 - 395, Japanese4p-B4-15 SiO_2マトリックス中のGe微粒子のラマン散乱
- 一般社団法人日本物理学会, 27 Mar. 1987, 年会講演予稿集, 42 (2), 401 - 401, Japanese29p-H-7 SiGe微粒子膜のラマン散乱II(表面・界面)
Books etc
- Others, ㈱シーエムシー･リサーチ, Mar. 2018, Japanese量子ドット・マイクロLEDディスプレイと関連材料の技術開発 (Technical Development of Quantum-dot・Micro LED Display and their Material)
Scholarly book
- Others, CRC Press, Aug. 2017, EnglishSilicon Nanomaterials Sourcebook, Low-Dimensional Structures Nanopowders, Nanowires
Scholarly book
- Others, 情報機構, Jun. 2017, Japanese量子ドット材料の技術と応用展開
Scholarly book
- Joint work, Wiley, Mar. 2017, English, ISBN: 9783527340378Micro- and Nanophotonic Technologies
Scholarly book
- Joint editor, Pan Stanford Publishing, Sep. 2016, English, ISBN: 9789814669764Silicon Nanophotonics - Basic Principles, Present Status, and Perspectives (Second Edition)
Scholarly book
- Joint work, InTech, Aug. 2016, English, ISBN: 9789535125761Zeolites - Useful Minerals
Scholarly book
- Joint work, シー エムシー出版, 2010, Japaneseナノシリコンの最新技術と応用展開
Scholarly book
- Joint work, Wiley-VCH, 2010, EnglishSilicon Nanocrystals: Fundamentals, Synthesis and Applications
Scholarly book
- Joint work, オーム社, 2006, Japaneseエコマテリアルハンドブック
Scholarly book
Presentations
- 第67回応用物理学会春季学術講演会, 14 Mar. 2020, Japanese, TOKYO, Japan, Domestic conferenceSpherical Silicon Nanoparticle Color Inks Enabled by Mie Resonances
Oral presentation
- 第67回応用物理学会春季学術講演会, 13 Mar. 2020, Japanese, TOKYO, Japan, Domestic conferenceColloidal Solution of Silicon Nanospheres for All Dielectric Metafluid
Oral presentation
- 第67回応用物理学会春季学術講演会, 13 Mar. 2020, Japanese, TOKYO, Japan, Domestic conferenceHydrogen evolution by silicon quantum dot photocatalyst
Oral presentation
- 2019年 神戸大学研究基盤センター「若手フロンティア研究会2019」, 19 Dec. 2019, Japanese, KOBE, Japan, Domestic conferenceMie 共鳴により発色するシリコンナノ粒子インク
Poster presentation
- 2019年 神戸大学研究基盤センター「若手フロンティア研究会2019」, 19 Dec. 2019, Japanese, KOBE, Japan, Domestic conferenceシリコン量子ドット光触媒による水素生成
Poster presentation
- 2019年 神戸大学研究基盤センター「若手フロンティア研究会2019」, 19 Dec. 2019, Japanese, KOBE, Japan, Domestic conferenceシリコン量子ドットの電気泳動
Poster presentation
- 2019年 神戸大学研究基盤センター「若手フロンティア研究会2019」, 19 Dec. 2019, Japanese, KOBE, Japan, Domestic conference高屈折率誘電体ナノディスクアレイの光学応答制御
Poster presentation
- 2019年 神戸大学研究基盤センター「若手フロンティア研究会2019」, 19 Dec. 2019, Japanese, KOBE, Japan, Domestic conferenceフォトクロミック色素を含む多層膜系の Fano 共鳴
Poster presentation
- 2019年 神戸大学研究基盤センター「若手フロンティア研究会2019」, 19 Dec. 2019, Japanese, KOBE, Japan, Domestic conference高屈折率誘電体ナノワイヤの光学特性
Poster presentation
- 第30回 光物性研究会, 2019, Japanese, KYOTO, Japan, Domestic conferenceDielectric Meta-atoms Exhibiting Optical Magnetism
Poster presentation
- 日本光学会ナノオプティクス研究グループ 第26回研究討論会, 2019, Japanese, TOKYO, Japan, Domestic conference球形シリコン Mie 共振器による光の指向性制御
[Invited]
Oral presentation
- MRS Fall Meeting & Exhibit, 2019, English, BOSTON, United States, International conference, Co-authored internationallyControlling Emission of WS2 Monolayer with a Spherical Silicon Mie Resonator
Oral presentation
- The International Symposium on Plasmonics and Nano-photonics (iSPN2019), 2019, English, KOBE, Japan, International conferenceEngineering directional scattering of Mie resonator
Poster presentation
- The International Symposium on Plasmonics and Nano-photonics (iSPN2019), 2019, English, KOBE, Japan, International conferenceColloidal Silicon Nanoresonators for All-Dielectric Photonics
Poster presentation
- 14th IEEE Nanotechnology Materials and Devices Conference (IEEE NMDC 2019), 2019, English, STOCKHPLM, Sweden, International conferenceDonor and Acceptor Pair Luminescence in Colloidal Silicon Quantum Dots
[Invited]
Oral presentation
- SemiconNano2019, 2019, English, KOBE, Japan, International conferenceDonor and Acceptor Pair Luminescence in Colloidal Silicon Quantum Dots
[Invited]
Oral presentation
- IUMRS-ICA 2019, 20th International Union of Materials Research Societies Conference, 2019, English, PERTH, Australia, International conferenceResonant Silicon Nanoparticles as Efficient Optical Nanoantennas
Oral presentation
- 第80回応用物理学会秋季学術講演会, 20 Sep. 2019, English, HOKKAIDO, Japan, Domestic conferencePhotochromic control of Fano resonance in multilayer structures
Poster presentation
- 第80回応用物理学会秋季学術講演会, 20 Sep. 2019, Japanese, HOKKAIDO, Japan, Domestic conferenceDirectional optical nanoantenna by an interference between Mie resonance of high-refractive-index dielectric nanosphere and LSPR of metal nanocap
Oral presentation
- 第80回応用物理学会秋季学術講演会, 20 Sep. 2019, Japanese, HOKKAIDO, Japan, Domestic conferenceSilicon Nanoparticle Ink Showing Color by Mie Resonance
Oral presentation
- 第80回応用物理学会秋季学術講演会, 20 Sep. 2019, Japanese, HOKKAIDO, Japan, Domestic conference, Co-authored internationallyControlling Emission of WS2 Monolayer with a Spherical Silicon Mie Resonator
Oral presentation
- 第80回応用物理学会秋季学術講演会, 19 Sep. 2019, Japanese, HOKKAIDO, Japan, Domestic conferenceCyclic Voltammetry of Silicon Quantum Dots
Oral presentation
- 第80回応用物理学会秋季学術講演会, 19 Sep. 2019, Japanese, HOKKAIDO, Japan, Domestic conferenceElectrophoresis of Silicon Quantum Dots
Oral presentation
- 第80回応用物理学会秋季学術講演会, 19 Sep. 2019, Japanese, HOKKAIDO, Japan, Domestic conferenceHydrogen Evolution by Silicon Quantum Dot Photocatalyst
Oral presentation
- 第80回応用物理学会秋季学術講演会, 19 Sep. 2019, Japanese, HOKKAIDO, Japan, Domestic conferenceColloidal Silicon Nanoparticles for Photonic Color Inks
Oral presentation
- 第80回応用物理学会秋季学術講演会, 19 Sep. 2019, Japanese, HOKKAIDO, Japan, Domestic conferenceFabrication of high-index dielectric nanodisk arrays and their optical responses (I)
Poster presentation
- 第80回応用物理学会秋季学術講演会, 18 Sep. 2019, Japanese, HOKKAIDO, Japan, Domestic conferenceHydrogen evolution by silicon quantum dot photocatalyst
Poster presentation
- MRS Spring Meeting & Exhibit, 2019, English, PHOENIX, United States, International conferenceSize Dependent Donor and Acceptor Pair Recombination in Colloidal Silicon Quantum Dots
Oral presentation
- MRS Spring Meeting & Exhibit, 2019, English, PHOENIX, United States, International conferenceHybridized Plasmonic Gap Mode in Gold Nanorod on Mirror Nanoantenna for Spectrally Tailored Emission Enhancement
Oral presentation
- The 7th International Conference on Light-Emitting Devices and Their Industrial Applications (LEDIA2019) in Optics & Photonics International Congress 2019, 2019, English, KANAGAWA, Japan, International conferenceLuminescence property of boron and phosphorus co-doped silicon quantum dots
[Invited]
Oral presentation
- 2018年 第66回応用物理学会春季学術講演会, 2018, Japanese, Domestic conference広範囲にサイズ制御したコロイドシリコンナノ粒子の光学特性
Invited oral presentation
- 2018年 第67回応用物理学会春季学術講演会, 2018, Japanese, Domestic conferenceホウ素とリンを同時ドープしたシリコン量子ドットの成長機構
Oral presentation
- 2018年 第68回応用物理学会春季学術講演会, 2018, Japanese, Domestic conferenceシリカナノ粒子塗布薄膜を用いたポータブル呼気センサ
Oral presentation
- 2018年 第65回応用物理学会春季学術講演会, 2018, Japanese, Domestic conferenceFano resonances in all-dielectric multilayer structure
Oral presentation
- 2017年第64回応用物理学会春季学術講演会, Mar. 2017, Japanese, 横浜市, Domestic conference不純物ドープシリコン量子ドットの単一ドット分光
Oral presentation
- 2017年第64回応用物理学会春季学術講演会, Mar. 2017, Japanese, 横浜市, Domestic conference不純物ドーピングによるシリコン量子ドットの輻射再結合レート増大(Ⅰ)
Oral presentation
- 2017年第64回応用物理学会春季学術講演会, Mar. 2017, Japanese, 横浜市, Domestic conference水分散性シリコン量子ドットベース光触媒材料の開発（Ⅰ）
Oral presentation
- 2017年第64回応用物理学会春季学術講演会, Mar. 2017, Japanese, 横浜市, Domestic conference水素終端全無機シリコンナノ結晶を用いた塗布型薄膜トランジスタ
Oral presentation
- 2017年第64回応用物理学会春季学術講演会, Mar. 2017, Japanese, 横浜市, Domestic conference金属イオンを用いた凝集制御によるシリコン量子ドット高次元構造の形成
Poster presentation
- 2017年第64回応用物理学会春季学術講演会, Mar. 2017, Japanese, 横浜市, Domestic conferenceシリコンナノ結晶塗布薄膜を用いた湿度センサの開発
Poster presentation
- 2017年第64回応用物理学会春季学術講演会, Mar. 2017, Japanese, 横浜市, Domestic conferenceシリコンナノ結晶塗布薄膜のガスセンサへの応用
Oral presentation
- 2017年第64回応用物理学会春季学術講演会, Mar. 2017, Japanese, 横浜市, Domestic conferenceSiナノ結晶塗布薄膜における抵抗変化現象
Oral presentation
- 2017年第64回応用物理学会春季学術講演会, Mar. 2017, Japanese, 横浜市, Domestic conferenceMetal Film Over Nanosphere構造におけるシリコン量子ドット単層膜の吸収断面積および発光再結合レートの同時増強
Oral presentation
- 2017年第64回応用物理学会春季学術講演会, Mar. 2017, Japanese, 横浜市, Domestic conferenceAtom Probe Tomographyによる不純物ドープシリコンナノ結晶の構造評価
Oral presentation
- 2017年第64回応用物理学会春季学術講演会, Mar. 2017, Japanese, 横浜市, Domestic conferenceAlナノキャップ構造の表面プラズモン共鳴による紫外アップコンバージョン増強
Oral presentation
- 2017年 第78回応用物理学会秋季学術講演会, 2017, Japanese, Domestic conference生体の第二光学窓領域に発光を示す水分散性シリコン量子ドット
Oral presentation
- 2017年 第78回応用物理学会秋季学術講演会, 2017, Japanese, Domestic conference水素終端シリコンナノ結晶塗布薄膜の光電流応答
Oral presentation
- 2017年 第78回応用物理学会秋季学術講演会, 2017, Japanese, Domestic conference金属イオンを用いたシリコン量子ドット高次構造の形成
Oral presentation
- 2017年 第78回応用物理学会秋季学術講演会, 2017, Japanese, Domestic conferenceナノ結晶塗布薄膜を利用した抵抗変化型呼気検出センサ
Oral presentation
- 2017年 第78回応用物理学会秋季学術講演会, 2017, Japanese, Domestic conferenceシリコン量子ドットの形状制御による基板上への配列制御
Oral presentation
- 2017年 第78回応用物理学会秋季学術講演会, 2017, Japanese, Domestic conferenceシリコンナノ結晶塗布薄膜によるフレキシブル抵抗変化型メモリ
Oral presentation
- 2017年 第78回応用物理学会秋季学術講演会, 2017, Japanese, Domestic conferenceコロイド状シリコン球の作製と誘電体ナノアンテナへの応用
Oral presentation
- 2017年 第78回応用物理学会秋季学術講演会, 2017, Japanese, Domestic conferenceコロイド状シリコンナノ粒子の広範囲サイズ制御とその光学特性
Oral presentation
- European Materials Research Society Spring Meeting and Exhibit, 2017, English, International conferenceSurface Plasmon Enhanced Photoluminescence from Silicon Quantum Dots Monolayer
Oral presentation
- 18th International Conference on Physics of Light-Matter Coupling in Nanostructures, 2017, English, International conferenceSize-Dependent Energy Level Structures in Donor and Acceptor Codoped Silicon Quantum Dots
Poster presentation
- 2017 European Materials Research Society Fall Meeting and Exhibit, 2017, English, International conferenceSilicon Quantum Dots and their Impact on Different Cell Types
Oral presentation
- 2017 European Materials Research Society Fall Meeting and Exhibit, 2017, English, International conferenceSilicon Nanocrystals in Highly Scattering Media -Broadband Enhancement of Effective Absorption Cross Section
Oral presentation
- 2017年 第78回応用物理学会秋季学術講演会, 2017, Japanese, Domestic conferenceMetal Nano Particle on Mirror構造におけるシリコン量子ドットの発光制御特性(III)
Oral presentation
- European Materials Research Society Spring Meeting and Exhibit, 2017, English, International conferenceFormation of Laminated Films of Silicon Quantum Dot Monolayers from the Colloidal Solution
Oral presentation
- 2017 European Materials Research Society Fall Meeting and Exhibit, 2017, English, International conferenceColloidal Si Nanospheres with Diameters Raging from 1 to 250 nm –Photoluminescence and Mie Resonances
Oral presentation
- IEEE SENSORS 2017, 2017, English, International conferenceBattery-Powered Wearable Respiration Sensor Chip with Nanocrystal Thin Film
Poster presentation
- 2017年 第78回応用物理学会秋季学術講演会, 2017, Japanese, Domestic conferenceAlを用いた金属ー誘電体多層膜系でのFano共鳴
Oral presentation
- The 2nd Workshop on Silicon-Based Micro- and Nano-Structures and Their Applications, Jan. 2017, English, Hangzhou,China, International conferenceSurface Plasmon Enhanced Photoluminescence from Silicon Quantum Dots
[Invited]
Invited oral presentation
- 神戸大学研究基盤センター「若手フロンティア研究会2016」, Dec. 2016, Japanese, 神戸市, Domestic conference有機分子によるP, B同時ドープSiナノ結晶の表面修飾
Poster presentation
- 神戸大学研究基盤センター「若手フロンティア研究会2016」, Dec. 2016, Japanese, 神戸市, Domestic conference有機色素脱色によるシリコン量子ドットの光触媒活性の評価
Poster presentation
- 神戸大学研究基盤センター「若手フロンティア研究会2016」, Dec. 2016, Japanese, 神戸市, Domestic conference磁場アセンブリ法による2次元ナノギャップ配列構造の自発的形成
Poster presentation
- 神戸大学研究基盤センター「若手フロンティア研究会2016」, Dec. 2016, Japanese, 神戸市, Domestic conference金属ナノ構造/シリコン量子ドット複合体の発光特性評価
Poster presentation
- 神戸大学研究基盤センター「若手フロンティア研究会2016」, Dec. 2016, Japanese, 神戸市, Domestic conference金ナノキャップ構造の表面プラズモン共鳴による希土類ドープナノ粒子のアップコ ンバージョン増強
Poster presentation
- 神戸大学研究基盤センター「若手フロンティア研究会2016」, Dec. 2016, Japanese, 神戸市, Domestic conference化学ドーピングによるシリコンナノ結晶コロイドの光学特性制御
Poster presentation
- 神戸大学研究基盤センター「若手フロンティア研究会2016」, Dec. 2016, Japanese, 神戸市, Domestic conferenceポーラスシリコンを用いた3次元微細曲面構造の形成
Poster presentation
- 神戸大学研究基盤センター「若手フロンティア研究会2016」, Dec. 2016, Japanese, 神戸市, Domestic conferenceボトムアップ法によるシリコンナノ結晶を用いた単電子トランジスタの作製
Poster presentation
- 神戸大学研究基盤センター「若手フロンティア研究会2016」, Dec. 2016, Japanese, 神戸市, Domestic conferenceシリコンナノ結晶塗布薄膜における表面状態と電気伝導特性の関係
Poster presentation
- 神戸大学研究基盤センター「若手フロンティア研究会2016」, Dec. 2016, Japanese, 神戸市, Domestic conferenceMNPoM構造におけるSi量子ドットの発光特性制御
Poster presentation
- 2016 MRS Fall Meeting & Exhibit, Nov. 2016, English, Boston,USA, International conferenceSurface Plasmon-Enhanced Upconversion in Rare-earth doped Nanoparticles with Au Nanocaps
Oral presentation
- 2016 MRS Fall Meeting & Exhibit, Nov. 2016, English, Boston,USA, International conferenceElectrical Characteristics of Codoped Silicon-Nanocrystal Films in Various Gas Environment
Oral presentation
- 2016 MRS Fall Meeting & Exhibit, Nov. 2016, English, Boston,USA, International conferenceControl of Light Emission from Silicon Quantum Dots Coupled to Plasmonic Nanoantennas
Oral presentation
- 8th International Conference on Nanomaterials -Research & Application, Oct. 2016, English, Brno,Czech Republic, International conferenceSurface Plasmon Enhanced Photoluminescence from Silicon Quantum Dots
[Invited]
Invited oral presentation
- International Conference on Self-Assembly in Confined Spaces, Oct. 2016, English, San Sebastian,Spain, International conferenceSpeccific Binding of Codoped Silicon Nanocrystal on Self-Assembled Monolayer
Poster presentation
- 第77回応用物理学会秋季学術講演会, Sep. 2016, Japanese, 新潟市, Domestic conference磁場アセンブリ法による2次元ナノギャップ配列構造の自発的形成
Oral presentation
- 第77回応用物理学会秋季学術講演会, Sep. 2016, Japanese, 新潟市, Domestic conference化学ドーピングによるシリコンナノ結晶コロイドの光学特性制御
Oral presentation
- 第77回応用物理学会秋季学術講演会, Sep. 2016, Japanese, 新潟市, Domestic conferenceシリコンナノ結晶・金ナノ結晶複合塗布薄膜の形成
Oral presentation
- 第77回応用物理学会秋季学術講演会, Sep. 2016, Japanese, 新潟市, Domestic conferenceシランカップリング反応によるシリコン量子ドットの表面修飾
Oral presentation
- The 14th International Conference on Near-Field Optics, Nanophotonics, and Related Techniques, Sep. 2016, English, 浜松市, International conferenceStructural Color Generation Based on Surface Plasmonic Resonance Using Self-assembled Array of Charged Nano-spheres
Poster presentation
- The 14th International Conference on Near-Field Optics, Nanophotonics, and Related Techniques, Sep. 2016, English, 浜松市, International conferenceSecond Harmonic Generation in Metal/Insulator/Metal Structure Consisting of Ge-doped SiO2 Thin Film as Insulator
Oral presentation
- The 26th biennial conference of the Condensed Matter Division of the European Physical Society, Sep. 2016, English, Groningen,The Netherlands, International conferenceLigand-free B and P co-doped Si quantum dots
[Invited]
Invited oral presentation
- 第77回応用物理学会秋季学術講演会, Sep. 2016, Japanese, 新潟市, Domestic conferenceFilm - coupled nanoparticle 構造におけるシリコンナノ結晶の発光特性(Ⅱ)
Oral presentation
- 第77回応用物理学会秋季学術講演会, Sep. 2016, Japanese, 新潟市, Domestic conferenceBiドープSiOxNy薄膜の近赤外発光特性
Oral presentation
- 第77回応用物理学会秋季学術講演会, Sep. 2016, Japanese, 新潟市, Domestic conferenceB,P 同時ドープシリコンナノ結晶塗布薄膜の光電流特性およびインピーダンス解析
Oral presentation
- European Materials Research Society, 2016 Spring Meeting, May 2016, English, Lille,France, International conferenceSynthesis of silicon-noble metal hybrid nanoparticle
Public symposium
- European Materials Research Society, 2016 Spring Meeting, May 2016, English, Lille,France, International conferenceSize-dependence of HOMO, LUMO and Fermi levels of B and P codoped Si nanocrystals
Public symposium
- 229th ECS Meeting, May 2016, English, San Diego,USA, International conferenceSilicon-Based Nano-Composites Made from All-Inorganic Colloidal Silicon Nanocrystal
[Invited]
Invited oral presentation
- European Materials Research Society, 2016 Spring Meeting, May 2016, English, Lille,France, International conferenceOrganic Functionalization of near-infrared luminescent silicon nanocrystals
Public symposium
- European Materials Research Society, 2016 Spring Meeting, May 2016, English, Lille,France, International conferenceMeasurement of absorption cross section of silicon nanomaterials: Do we lose or gain by dispersing bulk material into nanoparticles?
Public symposium
- European Materials Research Society, 2016 Spring Meeting, May 2016, English, Lille,France, International conferenceApplication of fluorescent co-doped silicon nanocrystals in cell biology
Public symposium
- 2016 MRS Spring Meeting & Exhibit, Apr. 2016, English, Phoenix,USA, International conferenceSurface Plasmon Enhanced Absorption Cross-Section of Silicon Quantum Dots in Gold Nanoparticle Composites
Poster presentation
- 2016 MRS Spring Meeting & Exhibit, Apr. 2016, English, Phoenix,USA, International conferenceSilicon nanocrystal-based metal-semiconductor hybrid nanoparticles
Public symposium
- 2016 MRS Spring Meeting & Exhibit, Apr. 2016, English, Phoenix,USA, International conferenceP and B Doped Silicon Nanocrystals in Biological Environment
Public symposium
- 2016 MRS Spring Meeting & Exhibit, Apr. 2016, English, Phoenix,USA, International conferenceConfinement of Donors and Doping Efficiency in Embedded and Freestanding Silicon Nanocrystals
Public symposium
- 2016 MRS Spring Meeting & Exhibit, Apr. 2016, English, Phoenix,USA, International conferenceColloidal Silicon Nanocrystals with High Boron and Phosphorus Concentration Shells
[Invited]
Invited oral presentation
- The 63th JSAP Spring Meeting, Mar. 2016, Japanese, The Japan Society of Applied Physics, 東京工業大学大岡山キャンパス, Domestic conferenceOptical properties of organic functionalized water-dispersible silicon nanocrystals
Oral presentation
- The 63th JSAP Spring Meeting, Mar. 2016, Japanese, The Japan Society of Applied Physics, 東京工業大学大岡山キャンパス, Domestic conferenceStructural Color Generation Based on Surface Plasmonic Resonance
Oral presentation
- The 63th JSAP Spring Meeting, Mar. 2016, Japanese, The Japan Society of Applied Physics, 東京工業大学大岡山キャンパス, Domestic conferenceLuminescence properties of bioconjugate of gold nanoparticle and silicon quantum dot
Oral presentation
- The 63th JSAP Spring Meeting, Mar. 2016, Japanese, The Japan Society of Applied Physics, 東京工業大学大岡山キャンパス, Domestic conferencePhotoluminescence properties of Au nanorod-Si quantum dot composites
Oral presentation
- The 63th JSAP Spring Meeting, Mar. 2016, Japanese, The Japan Society of Applied Physics, 東京工業大学大岡山キャンパス, Domestic conferenceUpconversion Enhancement of Rare-earth doped Nanoparticles with Au Nanocap
Oral presentation
- The 63th JSAP Spring Meeting, Mar. 2016, Japanese, The Japan Society of Applied Physics, 東京工業大学大岡山キャンパス, Domestic conferenceFabrication of preferentially oriented polycrystalline ZnO films on metal films and it’s second order nonlinear optical properties for plasmonic applications
Oral presentation
- 2016 MRS Spring Meeting & Exhibit, Mar. 2016, English, European Materials Research Society, Phoenix Convention Center, International conferenceSurface Plasmon Enhanced Absorption Cross-Section of Silicon Quantum Dots in Gold Nanoparticle Composites
Keynote oral presentation
- 2016 MRS Spring Meeting & Exhibit, Mar. 2016, English, European Materials Research Society, Phoenix Convention Center, International conferenceSilicon nanocrystal-based metal-semiconductor hybrid nanoparticles
Keynote oral presentation
- 2016 MRS Spring Meeting & Exhibit, Mar. 2016, English, European Materials Research Society, Phoenix Convention Center, International conferenceP and B Doped Silicon Nanocrystals in Biological Environment
Keynote oral presentation
- The 63th JSAP Spring Meeting, Mar. 2016, Japanese, The Japan Society of Applied Physics, 東京工業大学大岡山キャンパス, Domestic conferenceSecond harmonic generation from metal-insulator-metal(MIM) consisting of Ge doped SiO2 thin film as insulator
Oral presentation
- The 63th JSAP Spring Meeting, Mar. 2016, Japanese, The Japan Society of Applied Physics, 東京工業大学大岡山キャンパス, Domestic conferenceLuminescence properties of Si nanocrystals in film - coupled nanoparticle
Oral presentation
- 2016 MRS Spring Meeting & Exhibit, Mar. 2016, English, European Materials Research Society, Phoenix Convention Center, International conferenceColloidal Silicon Nanocrystals with High Boron and Phosphorus Concentration Shells
[Invited]
Invited oral presentation
- The 63th JSAP Spring Meeting, Mar. 2016, Japanese, The Japan Society of Applied Physics, 東京工業大学大岡山キャンパス, Domestic conferenceEnergy level structure of boron and phosphorus codoped silicon nanocrystals（Ⅱ）
Oral presentation
- The 63th JSAP Spring Meeting, Mar. 2016, Japanese, The Japan Society of Applied Physics, 東京工業大学大岡山キャンパス, Domestic conferenceObservation of Coulomb Blockade on B and P Codoped Si Nanocrystals
Oral presentation
- The 63th JSAP Spring Meeting, Mar. 2016, Japanese, The Japan Society of Applied Physics, 東京工業大学大岡山キャンパス, Domestic conferenceSurface functionalization of P and B codoped silicon nanocrystals by allylamine
Oral presentation
- 若手フロンティア研究会2015, Dec. 2015, Japanese, 神戸大学 百年記念会館, Domestic conference金ナノ粒子シリコンナノ結晶複合体の発光特性評価
Poster presentation
- 若手フロンティア研究会2015, Dec. 2015, Japanese, 神戸大学 百年記念会館, Domestic conferenceビスマスドープシリコンナイトライド薄膜の近赤外発光特性
Poster presentation
- 第26回光物性研究会, Dec. 2015, Japanese, 神戸大学 百年記念会館, Domestic conferenceシリコンナノ結晶塗布薄膜の光電流特性
Poster presentation
- 若手フロンティア研究会2015, Dec. 2015, Japanese, 神戸大学 百年記念会館, Domestic conferenceシリコンナノ結晶塗布薄膜の光電流特性
Poster presentation
- 第26回光物性研究会, Dec. 2015, Japanese, 神戸大学 百年記念会館, Domestic conferenceシリコンナノ結晶ソリッドにおけるナノ結晶間エネルギー移動
Poster presentation
- Nanophotonics in Asia 2015, Dec. 2015, Japanese, 大阪大学中之島センター, International conferenceUpconversion Luminescence of Rare-Earth-Doped Y2O3 Nanoparticle with Metal Nano-Cap
Poster presentation
- 若手フロンティア研究会2015, Dec. 2015, Japanese, 神戸大学 百年記念会館, Domestic conferenceEnhancement of SHG from Ge-doped SiO2 by metal-insulator-metal structure
Poster presentation
- Nanophotonics in Asia 2015, Dec. 2015, Japanese, 大阪大学中之島センター, International conferenceEnhancement of SHG from Ge-doped SiO2 by metal-insulator-metal structure
Poster presentation
- 第26回光物性研究会, Dec. 2015, Japanese, 神戸大学 百年記念会館, Domestic conferenceDielectric-loaded surface plasmon polaritonによる配向多結晶ZnO薄膜のSHG増強
Poster presentation
- 若手フロンティア研究会2015, Dec. 2015, Japanese, 神戸大学 百年記念会館, Domestic conferenceB,P同時ドープシリコンナノ結晶のエネルギー準位構造
Poster presentation
- 第26回光物性研究会, Dec. 2015, Japanese, 神戸大学 百年記念会館, Domestic conferenceAtomi Layer Deposition法による誘電体多層膜粒子の作製及び光の状態密度制御
Poster presentation
- Workshop on "Silicon Nanocrystals -Fundamental Physics, Plasmonic Nano-composites, Biomedical Applications", Nov. 2015, English, International conferenceMetal/silicon-nanocrystal-doupled system Ⅰ- radiative rate engineering
Keynote oral presentation
- Workshop on "Silicon Nanocrystals -Fundamental Physics, Plasmonic Nano-composites, Biomedical Applications", Nov. 2015, English, Kobe University, International conferenceAll-Inorganic colloidal silicon nanocrystals
Keynote oral presentation
- One-day Czech-Japan Workshop on Nanoparticles fo Bio-Applications, Sep. 2015, English, Pilsen, International conferenceComposites of water dispersible silicon nanocrystals
[Invited]
Invited oral presentation
- The 77th JSAP Autumn Meeting, Sep. 2015, Japanese, The Japan Society of Applied Physics, 名古屋国際会議場, Domestic conferenceLuminescence properties of dielectric multilayered particles prepared by Atomic Layer Deposition
Oral presentation
- Workshop on Nanomaterials for Energy Applications, Sep. 2015, English, Advanced Industrial Science and TEchnology, Tsukuba, International conferenceAll-inorganic colloidal silicon nanocrystals -surface modification by boron and phosphorus co-doping
[Invited]
Invited oral presentation
- European Materials Research Society 2015 Fall Meeting, Sep. 2015, English, European Materials Research Society, Warsaw, International conferenceAll-inorganic colloidal silicon nanocrystals -surface modification by boron and phosphorus co-doping
[Invited]
Invited oral presentation
- European Materials Research Society 2015 Spring Meeting, May 2015, English, European Materials Research Society, Lille, International conferenceStructure and optical properties of B and P co-doped Si nanocrystals
[Invited]
Invited oral presentation
- 第６２回応用物理学会春季学術講演会, 2015, Japanese, Domestic conference水蒸気酸化によるポーラスシリコンの3次元構造形成
Oral presentation
- 電子情報通信学会 シリコン材料・デバイス研究会, 2015, Japanese, Domestic conference空孔率制御によるポーラスシリコン膜の自己組織的3次元微細構造形成
Oral presentation
- 第６２回応用物理学会春季学術講演会, 2015, Japanese, Domestic conference金ナノ粒子-シリコンナノ結晶複合体の発光特性（I)
Oral presentation
- 第６２回応用物理学会春季学術講演会, 2015, Japanese, Domestic conferenceプラズモニック多層ナノ粒子によるアップコンバージョン増強(I)
Oral presentation
- 2015年電子情報通信学会総合大会, 2015, Japanese, Domestic conferenceシリコンナノ結晶の多様な発光特性と医療・バイオ応用への期待
Invited oral presentation
- 第６２回応用物理学会春季学術講演会, 2015, Japanese, Domestic conferenceシリコンナノ結晶ソリッドにおけるナノ結晶間相互作用(Ⅱ)
Oral presentation
- 第６２回応用物理学会春季学術講演会, 2015, Japanese, Domestic conferenceシリコンナノ結晶コロイド塗布薄膜の形成と評価（II）
Oral presentation
- 2014年第61回応用物理学会春季学術講演会, 2014, Japanese, Domestic conference塗布によるSiナノ結晶薄膜の作製 (Ⅰ)
Oral presentation
- 第75回応用物理学会秋季学術講演会, 2014, Japanese, Domestic conference第二次高調波発生によるGeO2多結晶の配向方向決定
Oral presentation
- 第25回光物性研究会(2014), 2014, Japanese, Domestic conference第二次高調波発生によるGeO2多結晶のイメージング解析
Poster presentation
- 神戸大学研究基盤センター「 若手フロンティア研究会２０１４ 」, 2014, Japanese, Domestic conference全無機コロイド状シリコンゲルマニウムナノ結晶の作製と評価
Poster presentation
- 第75回応用物理学会秋季学術講演会, 2014, Japanese, Domestic conference銀ナノキャップ構造による希土類ドープナノ粒子のアップコンバージョン発光増強
Oral presentation
- 第25回光物性研究会(2014), 2014, Japanese, Domestic conference金属ナノキャップを有する希土類ドープY2O3ナノ粒子のアップコンバージョン発光
Poster presentation
- 神戸大学研究基盤センター「 若手フロンティア研究会２０１４ 」, 2014, Japanese, Domestic conference金属ナノキャップを有する希土類ドープY2O3アップコンバージョンナノ粒子の開発
Poster presentation
- 2014年第61回応用物理学会春季学術講演会, 2014, Japanese, Domestic conferenceラマン散乱によるB,P同時ドープコロイド状Siナノ結晶の構 造評価
Oral presentation
- 2014年第61回応用物理学会春季学術講演会, 2014, Japanese, Domestic conferenceパルスレーザー照射によるシリコンナノ結晶の表面改質
Oral presentation
- 神戸大学研究基盤センター「 若手フロンティア研究会２０１４ 」, 2014, Japanese, Domestic conferenceシリコンナノ結晶塗布膜の形成と評価
Poster presentation
- 第75回応用物理学会秋季学術講演会, 2014, Japanese, Domestic conferenceシリコンナノ結晶ソリッドにおけるナノ結晶間相互作用
Oral presentation
- 第75回応用物理学会秋季学術講演会, 2014, Japanese, Domestic conferenceシリコンナノ結晶コロイド塗布薄膜の形成と評価
Oral presentation
- 第75回応用物理学会秋季学術講演会, 2014, Japanese, Domestic conferenceコロイド状Si1-xGex ナノ結晶の塗布によるナノ結晶薄膜の作製と評価（I）
Oral presentation
- 2014年第61回応用物理学会春季学術講演会, 2014, Japanese, Domestic conferenceコロイド状Si1-xGex ナノ結晶の作製と光学特性（II）
Oral presentation
- 2014 MRS Fall Meeting & Exhibit, 2014, English, International conferenceUpconversion from Rare-Earth Doped Y2O3 Nanoparticles with Metal Nano-Caps
Oral presentation
- 2014 MRS Fall Meeting & Exhibit, 2014, English, International conferenceSynthesis of n- and/or p-type Impurity Doped Silicon Nanocrystals from Hydrogen Silsesquioxane
Poster presentation
- 第75回応用物理学会秋季学術講演会, 2014, Japanese, Domestic conferenceSiNx薄膜による第二次高調波発生
Oral presentation
- Kista Science Seminars, 2014, English, International conferenceSilicon Nanocrystals as Optoelectronic Materials
Public discourse
- 2014 MRS Fall Meeting & Exhibit, 2014, English, International conferenceSecond harmonic generation in amorphous Si-rich silicon nitride thin films with a wide range of Si concentration
Poster presentation
- 2014 MRS Fall Meeting & Exhibit, 2014, English, International conferenceSecond harmonic generation from amorphous Gex(SiO2)1-x thin films
Poster presentation
- 2014 MRS Fall Meeting & Exhibit, 2014, English, International conferenceRoom Temperature Imprinting of Nano-porous Glass Prepared from Phase-Separated Glass
Poster presentation
- 2014 MRS Fall Meeting & Exhibit, 2014, English, International conferencePolrization-sensitive second harmonic generation of a-quartz like GeO2 polycrystals
Poster presentation
- 2014 MRS Spring Meeting & Exhibit, 2014, English, International conferenceControlling HOMO-LUMO Gap of Colloidal Silicon Nanocrystals in a Wide Range by n- and p-Type Impurity Codoping
Poster presentation
- Tossa workshop 2014 – Silicon Nanocrystals: Science and Applications, 2014, English, International conferenceBoron and Phosphorus Codoped All-Inorganic Colloidal Silicon Nanocrystals
Nominated symposium
- 2014 MRS Spring Meeting & Exhibit, 2014, English, International conferenceAll-Inorganic Colloidal Silicon Nanocrystals-Surface Modification by Heavy Doping of Boron and Phosphorus
Oral presentation
- One-day Czech-Japan Workshop on Advancement of Silicon Nanophotonics I, 2014, English, International conferenceAll-Inorganic Colloidal Silicon Nanocrystals
Nominated symposium
- Workshop on "Advancement of Group IV Nanostructures Nanophotonics and Nanoelectronics", 2014, English, International conferenceAll-Inorganic Colloidal Silicon Nanocrystal
Nominated symposium
- 第24回日本MRS年次大会, 2014, Japanese, Domestic conferenceAll-inorganic Colloidal Silicon Germanium Alloy Nanocrystals with the Formation of High Boron and Phosphorus Concentration Hydrophilic Shell
Poster presentation
- 2014 MRS Spring Meeting & Exhibit, 2014, English, International conferenceAll-inorganic Colloidal Silicon Germanium Alloy Nanocrystals -High Solution Dispersibility by the Formation of High Boron and Phosphorus Concentration Shell-
Poster presentation
- 春季第60回応用物理学会講演会, Mar. 2013, Japanese, 応用物理学会, 神奈川県, Domestic conference誘電体多層膜粒子の作製及びその発光特性
Oral presentation
- 春季第60回応用物理学会講演会, Mar. 2013, Japanese, 応用物理学会, 神奈川県, Domestic conference有機分子表面修飾無しで極性溶媒分散性を有するP,B同時ドープSiナノ結晶
Oral presentation
- 春季第60回応用物理学会講演会, Mar. 2013, Japanese, 応用物理学会, 神奈川県, Domestic conference表面修飾無しで水分散性を有するSiナノ結晶
Oral presentation
- 春季第60回応用物理学会講演会, Mar. 2013, Japanese, 応用物理学会, 神奈川県, Domestic conference表面修飾基を持たないP,B同時ドープSiナノ結晶コロイド
Oral presentation
- 春季第60回応用物理学会講演会, Mar. 2013, Japanese, 応用物理学会, 神奈川県, Domestic conference金属ハーフシェル構造によるY2O3:Er,Ybナノ粒子のアップコンバージョン発光増強
Oral presentation
- 春季第60回応用物理学会講演会, Mar. 2013, Japanese, 応用物理学会, 神奈川県, Domestic conference近赤外-可視発光Siナノ結晶コロイドの開発
Oral presentation
- 春季第60回応用物理学会講演会, Mar. 2013, Japanese, 応用物理学会, 神奈川県, Domestic conferenceビスマスドープシリコンオキシナイトライド薄膜の近赤外発光（II）
Oral presentation
- 春季第60回応用物理学会講演会, Mar. 2013, Japanese, 応用物理学会, 神奈川県, Domestic conferenceコロイド状Geナノ結晶の作製と光学特性(II)
Oral presentation
- 春季第60回応用物理学会講演会, Mar. 2013, Japanese, 応用物理学会, 神奈川県, Domestic conferencePhotosensitization of europium ions by silver clusters in zeolite
Oral presentation
- 春季第60回応用物理学会講演会, Mar. 2013, Japanese, 応用物理学会, 神奈川県, Domestic conferenceGeドープシリカ薄膜からの第2次高調波発生
Oral presentation
- 第24回光物性研究会(2013), 2013, Japanese, Domestic conference誘電体多層膜粒子による光の状態密度制御
Poster presentation
- 第74回応用物理学会秋季学術講演会, 2013, Japanese, Domestic conference分相性ポーラスガラスの室温インプリント加工による光学素子作製
Oral presentation
- 2013年度精密工学会秋季大会学術講演会, 2013, Japanese, Domestic conference不純物ドーピングによるシリコンナノ結晶の物性制御
[Invited]
Invited oral presentation
- 第74回応用物理学会秋季学術講演会, 2013, Japanese, Domestic conference化学センシングに向けた室温インプリント加工によるポーラスシリカマイクロチューブの作製と光学特性評価
Oral presentation
- 第74回応用物理学会秋季学術講演会, 2013, Japanese, Domestic conferenceコロイド状 SiGe ナノ結晶の作製と光学特性(I)
Oral presentation
- 第24回光物性研究会(2013), 2013, Japanese, Domestic conferenceSiNｘ薄膜による第2次高調波発生とその起源
Poster presentation
- 第74回応用物理学会秋季学術講演会, 2013, Japanese, Domestic conferenceSiNｘ薄膜による第2次高調波発生
Oral presentation
- 第74回応用物理学会秋季学術講演会, 2013, Japanese, Domestic conferencen型、p型不純物同時ドーピングによる近赤外-可視発光コロイド状Siナノ結晶の開発
Oral presentation
- European Materials Research Society, Spring Meeting, 2013, English, International conferenceNear-infrared luminescent silicon nanocrystals dispersible in water without surface functionalization
Poster presentation
- 223rd ECS meeting, 2013, English, International conferencen- and p-type impurity co-doped and compensated Si nanocrystals in silicate and in solution
[Invited]
Invited oral presentation
- Growth of Impurity-doped Group IV Semiconductor Nanocrystals by Sputtering, 2013, English, International conferenceGrowth of Impurity-doped Group IV Semiconductor Nanocrystals by Sputtering
[Invited]
Invited oral presentation
- 第24回光物性研究会(2013), 2013, Japanese, Domestic conferenceGex(SiO2)1-x薄膜からの第2次高調波発生
Poster presentation
- 2013 MRS Fall Meeting & Exhibit, 2013, English, International conferenceEu-doping Induced Improvement on the Second Harmonic Generation of ZnO Nanowires
Oral presentation
- 2013 MRS Fall Meeting & Exhibit, 2013, English, International conferenceEnhanced Red Luminescence of Rare Earth Ions by Silver Clusters/Ions in Zeolites
Oral presentation
- 2013 MRS Fall Meeting & Exhibit, 2013, English, International conferenceControl of Photonic Mode Density inside a Core of a Multi-Layered Dielectric Sphere
Oral presentation
- 2013 JSAP-MRS Joint Symposia, 2013, English, Domestic conferenceControl of photoluminescence properties of rare earth ions in the core of a multi-layered dielectric sphere
Oral presentation
- European Materials Research Society, Spring Meeting, 2013, English, International conferenceColloidal silicon nanocrystals with inorganic atomic ligands
Oral presentation
- International Conference on Solid State Devices and Materials (SSDM-2013), 2013, English, Domestic conferenceAluminum Doped Core-Shell Type ZnO/ZnS Nanowires: Structural and Photoluminescence Studies
Oral presentation
- 2013年度東北大学金属材料研究所ワークショップ「格子欠陥が挑戦する新エネルギー・環境材料開発」, 2013, Japanese, Domestic conferenceAll-Inorganic Near-Infrared Luminescent Colloidal Silicon Nanocrystals -High Dispersibility in Polar Liquid by Phosphorus and Boron Co-doping
[Invited]
Invited oral presentation
- 第23回日本MRS年次大会, 2013, Japanese, Domestic conferenceAll-Inorganic Near-Infrared Luminescent Colloidal Silicon Nanocrystals
Poster presentation
- 第349回蛍光体同学会講演会, 2013, Japanese, Domestic conferenceAg クラスター\／Ag イオンと希土類イオンを 共添加したゼオライトの発光特性
[Invited]
Invited oral presentation
- 第23回光物性研究会, Dec. 2012, Japanese, 光物性研究会, 大阪府, Domestic conference誘電体多層膜フォトニック粒子による光の状態密度制御
Poster presentation
- 第23回光物性研究会, Dec. 2012, Japanese, 光物性研究会, 大阪府, Domestic conference有機分子による表面修飾無しで極性溶媒分散性を有する P、B 同時ドープ Si ナノ結晶の近赤外発光特性
Poster presentation
- 光エレクトロニクス研究会, Dec. 2012, Japanese, 電気通情報通信学会, 東京都, Domestic conference不純物をドープしたSiナノ結晶の3次の非線形光学応答-Biドーピングによる非線形光学応答の増強
Oral presentation
- 第23回光物性研究会, Dec. 2012, Japanese, 光物性研究会, 大阪府, Domestic conferencePhotosensitization of europium ions by silver clusters in zeolite
Poster presentation
- Pacific Rim Meeting on Electrochemical and Solid-state Science (PRiME) 2012, Oct. 2012, English, The Electrochemical Society, Honolulu, USA, International conferenceThree-Dimensional Structure of (110) Porous Silicon with In-Plane Optical Birefringence
Oral presentation
- 秋季第75回 応用物理学会学術講演会, Sep. 2012, Japanese, 応用物理学会, 愛媛県, Domestic conference誘電体多層膜フォトニック粒子による発光制御
Oral presentation
- 秋季第77回 応用物理学会学術講演会, Sep. 2012, Japanese, 応用物理学会, 愛媛県, Domestic conference表面修飾無しで極性溶媒分散性を有するSiナノ結晶
Oral presentation
- 秋季第74回 応用物理学会学術講演会, Sep. 2012, Japanese, 応用物理学会, 愛媛県, Domestic conferenceナノポーラスシリコンの室温インプリント加工によるテラヘルツ帯ワイヤグリッド偏光子作製
Oral presentation
- 秋季第78回 応用物理学会学術講演会, Sep. 2012, Japanese, 応用物理学会, 愛媛県, Domestic conferenceコロイド状Geナノ結晶の作製と光学特性（Ⅰ）
Oral presentation
- IUMRS-International Conference on Electronic Materials 2013, Sep. 2012, English, International Union of Materials Research Societies, Yokohama, International conferenceUpconversion luminescence of Er and Yb co-doped NaYF4 nanoparticles with metal shells
Oral presentation
- 秋季第76回 応用物理学会学術講演会, Sep. 2012, Japanese, 応用物理学会, 愛媛県, Domestic conferenceP,B同時ドープSiナノ結晶ソリッドの作製と発光特性
Oral presentation
- IUMRS-International Conference on Electronic Materials 2012, Sep. 2012, English, International Union of Materials Research Societies, Yokohama, International conferenceEnhancement of upconversion luminescence of Al2O3: Er3+, Yb3+ thin films by small assemblies of Au nanorods
Oral presentation
- Nanophotonics in Asia 2012, Sep. 2012, English, Advanced Nano Photonics Research and Education Center in Asia, Kanazawa, International conferenceControl of photonic mode density inside a core of a multi-layered sphere as a new three dimensional photonic crystal
Poster presentation
- 秋季第73回 応用物理学会学術講演会, Sep. 2012, Japanese, 応用物理学会, 愛媛県, Domestic conferenceBiドープシリコンオキシナイトライド薄膜の近赤外発光特性（Ⅰ）
Oral presentation
- 第17回シリコンフォトニクス研究会, Jul. 2012, Japanese, シリコンフォトニクス時限専門研究会, 神戸市, Domestic conference不純物ドーピングによるシリコンナノ結晶の物性制御
Invited oral presentation
- ナノ学会第10回大会, Jun. 2012, Japanese, ナノ学会, 大阪府, Domestic conference誘電体多層膜粒子による三次元フォトニック結晶の作製
Oral presentation
- ナノ学会第11回大会, Jun. 2012, Japanese, ナノ学会, 大阪府, Domestic conferenceゼオライト／ポリマー近赤外発光透明コンポジットの作製
Oral presentation
- Fifth Internatinal Conference on Optical, Optoelectronic and Photonic Materials and Applications 2012, Jun. 2012, English, ICOOPMA14, Nara, Japan, International conferencePhotoluminescence Properties of Phosphorus and Boron Codoped Silicon Quantum Dots dispersed in solution
Poster presentation
- Fifth Internatinal Conference on Optical, Optoelectronic and Photonic Materials and Applications 2012, Jun. 2012, English, ICOOPMA13, Nara, Japan, International conferenceNon-Resonant Third Order Nonlinear Optical Responses of Impurity-Doped Silicon Nanocrystals
Oral presentation
- Fifth Internatinal Conference on Optical, Optoelectronic and Photonic Materials and Applications 2012, Jun. 2012, English, ICOOPMA12, Nara, Japan, International conferenceLuminescence Properties of Bismuth-doped Oxidized Nanoporous Silicon Thin Films
Poster presentation
- Fifth Internatinal Conference on Optical, Optoelectronic and Photonic Materials and Applications 2012, Jun. 2012, English, ICOOPMA15, Nara, Japan, International conferenceAll-inorganic Near Infrared Luminescent Colloidal Silicon Quantum Dot
Oral presentation
- Silicon in space, May 2012, English, Laboratory Astrophysics and Cluster Physics Group, Loveno di Menaggio, Italy, International conferenceOptical properties of impurity-doped silicon nanocrystals
[Invited]
Invited oral presentation
- Materials Research Society 2014 Spring Meeting, Apr. 2012, English, Materials Research Society, San Francisco, USA, International conferenceSurfactant-free silicon nanocrystal colloids -controlling dispersibility of silicon nanocrystals in polar liquids by impurity doping
Oral presentation
- Materials Research Society 2012 Spring Meeting, Apr. 2012, English, Materials Research Society, San Francisco, USA, International conferenceNonlinear Optical Properties of Impurity Doped Silicon Nanocrystals
Oral presentation
- Materials Research Society 2013 Spring Meeting, Apr. 2012, English, Materials Research Society, San Francisco, USA, International conferenceExperimental Determination of the Location of Electrically Active Boron Atoms in Boron-doped Silicon Nanocrystals
Oral presentation
- 春季第59回応用物理学会講演会, Mar. 2012, Japanese, 応用物理学会, 早稲田大学 早稲田キャンパス, Domestic conference誘電体多層膜粒子によるアップコンバージョン発光増強
Oral presentation
- 春季第59回応用物理学会講演会, Mar. 2012, Japanese, 応用物理学会, 早稲田大学 早稲田キャンパス, Domestic conference表面修飾無しで極性溶媒に高い分散性を有するSiナノ結晶コロイド(II)
Oral presentation
- 平成23年度 イノベーション推進事業成果報告会, Mar. 2012, Japanese, 神戸大学連携創造本部, 神戸市, Domestic conference深紫外-遠赤外光用サブ波長構造光学素子の開発
Oral presentation
- 春季第59回応用物理学会講演会, Mar. 2012, Japanese, 応用物理学会, 早稲田大学 早稲田キャンパス, Domestic conferenceナノポーラスシリコンへの室温インプリント加工によるテラヘルツ帯ワイヤグリッド偏光子作製
Poster presentation
- 春季第59回応用物理学会講演会, Mar. 2012, Japanese, 応用物理学会, 早稲田大学 早稲田キャンパス, Domestic conferencePhosphorus ドーピングによるSiliconナノ結晶の非共鳴非線形光学応答の増強
Poster presentation
- 春季第59回応用物理学会講演会, Mar. 2012, Japanese, 応用物理学会, 早稲田大学 早稲田キャンパス, Domestic conferenceAgオーバーレイヤによるY2O3;Yb,Er粒子のアップコンバージョン発光増強
Oral presentation
- 光エレクトロニクス研究会, Dec. 2011, Japanese, 光エレクトロニクス専門委員会, 東京都港区 機械振興会館, Domestic conference紫外光用ポーラスシリカトゥルーゼロオーダー波長板
Oral presentation
- 若手フロンティア研究会2012, Dec. 2011, Japanese, 神戸大学研究基盤センター, 神戸市, Domestic conferenceビスマスドープシリカ/シリコンリッチシリカ多層膜からの近赤外発光
Poster presentation
- Workshop on Innovation and Pioneering Technology 2011, Dec. 2011, English, Kobe University, KOBE University Centennial Hall, International conferenceThree-dimensional structures of (110) porous silicon with in-plane optical birefringence
Poster presentation
- Workshop on Innovation and Pioneering Technology 2011, Dec. 2011, English, Kobe University, KOBE University Centennial Hall, International conferenceSolution-dispersible and near-infrared emitting Si nanocrystal without surface functionalization
Poster presentation
- Workshop on Innovation and Pioneering Technology 2011, Dec. 2011, English, Kobe University, 神戸市, International conferenceLuminescence properties of Bi-doped oxidized porous silicon thin films
Poster presentation
- 2nd International Conference on Advanced Nanomaterials and Nanotechnology, Dec. 2011, English, Indian Institute of Technology Guwahati, Guwahati, India, International conferenceLinear and non-linear optical properties of donor and/or acceptor doped silicon nanocrystals
Invited oral presentation
- Workshop on Innovation and Pioneering Technology 2011, Dec. 2011, English, Kobe University, KOBE University Centennial Hall, International conferenceEnhancement of upconversion luminescence of Al2O3: Er3+; Yb3+ thin films by small assemblies of Au nanorods
Poster presentation
- Workshop on Innovation and Pioneering Technology 2011, Dec. 2011, English, Kobe University, KOBE University Centennial Hall, International conferenceBroadband near infrared luminescence from Bi-doped silica/Si rich SiO2 multilayer film
Poster presentation
- 若手フロンティア研究会2011, Dec. 2011, Japanese, 神戸大学研究基盤センター, 神戸大学百年記念館, Domestic conferenceBroadband near infrared emission in Bi-doped oxidized nanoporous silicon thin films
Poster presentation
- 若手フロンティア研究会2011, Dec. 2011, Japanese, 神戸大学研究基盤センター, 神戸大学百年記念館, Domestic conferenceAuナノロッドの表面プラズモン励起によるEr,Yb共添加Al2O3薄膜のアップコンバージョン発光増強
Poster presentation
- Workshop on Innovation and Pioneering Technology 2011, Dec. 2011, English, Kobe University, KOBE University Centennial Hall, International conferenceAcceptor-related photoluminescence from B-doped Si nanocrystals
Poster presentation
- 若手フロンティア研究会2011, Dec. 2011, Japanese, 神戸大学研究基盤センター, 神戸大学百年記念館, Domestic conference(110)ポーラスシリコンの三次元構造解析
Poster presentation
- 第16回シリコンフォトニクス研究会, Nov. 2011, Japanese, シリコンフォトニクス時限専門研究会, 電気通信大学, Domestic conference有機分子表面修飾無しで極性溶媒分散性を有するシリコンナノ結晶コロイドの開発
Poster presentation
- Materials Research Society 2011 Fall Meeting, Nov. 2011, English, Materials Research Society, Boston, USA, International conferenceZero-Phonon Optical Transitions in Si Nanocrystals
Oral presentation
- 2011 Materials Research Society Fall Meeting, Nov. 2011, English, Materials Research Society, Hynes Convention Center, Boston, USA, International conferenceBroadband near-Infrared Luminescence from Bi-Doped Zeolite-Polymer Composites
Poster presentation
- 2011 Materials Research Society Fall Meeting, Nov. 2011, English, Materials Research Society, Hynes Convention Center, Boston, USA, International conferenceAll-Inorganic Solution-Dispersible Silicon Nanocrystals-Controlling Dispersibility by Impurity Doping
Poster presentation
- 第72回 応用物理学会学術講演会, Sep. 2011, Japanese, 応用物理学会, 山形県, Domestic conference面内に屈折率異方性を有するポーラスシリコンの三次元構造解析
Oral presentation
- 第72回 応用物理学会学術講演会, Sep. 2011, Japanese, 応用物理学会, 山形県, Domestic conferenceアモルファスシリコン固相結晶化の成膜条件依存性
Oral presentation
- 第72回 応用物理学会学術講演会, Sep. 2011, Japanese, 応用物理学会, 山形県, Domestic conferenceOptical properties of bismuth-doped pure nanoporous silica thin film
Poster presentation
- 第72回 応用物理学会学術講演会, Sep. 2011, Japanese, 応用物理学会, 山形県, Domestic conferenceDoping concentration dependence of the optical properties of bismuth doped zeolites
Poster presentation
- 第72回 応用物理学会学術講演会, Sep. 2011, Japanese, 応用物理学会, 山形大学 小白川キャンパス, Domestic conferenceBoronドーピングによるSiliconナノ結晶の非線形光学特性の向上
Oral presentation
- 第72回 応用物理学会学術講演会, Sep. 2011, Japanese, 応用物理学会, 山形大学 小白川キャンパス, Domestic conferenceBiドープシリカ/シリコンリッチシリカ多層膜の近赤外発光特性
Poster presentation
- European Materials Research Society (E-MRS) 2011 Fall Meeting, Sep. 2011, English, Europian Materials Research Society, Warsaw, Poland, International conferenceBi-doped nano-fluorescence materials
[Invited]
Invited oral presentation
- 第72回 応用物理学会学術講演会, Sep. 2011, Japanese, 応用物理学会, 山形大学 小白川キャンパス, Domestic conferenceAuナノロッドの表面プラズモン励起によるEr,Yb共添加Al2O3薄膜のアップコンバージョン発光増強
Poster presentation
- ナノ学会第9会大会, Jun. 2011, Japanese, ナノ学会, 北海道大学 学術交流会館, Domestic conference溶液中に分散したP,B同時ドープSiナノ結晶の発光特性
Poster presentation
- ナノ学会第9会大会, Jun. 2011, Japanese, ナノ学会, 北海道, Domestic conference溶液に分散したP,B同時ドープSiナノ結晶の発光特性
Oral presentation
- ナノ学会第9会大会, Jun. 2011, Japanese, ナノ学会, 北海道大学 学術交流会館, Domestic conference溶液に分散したBドープSiナノ結晶の発光特性
Poster presentation
- ナノ学会第9会大会, Jun. 2011, Japanese, ナノ学会, 北海道, Domestic conference紫外光用異方性ナノ構造トゥルーゼロオーダー波長板
Poster presentation
- はりま産学交流会 創造例会, May 2011, Japanese, はりま産学交流会, 姫路商工会議所, Domestic conferenceポーラスシリコン・ポーラスシリカサブ波長光学素子
Invited oral presentation
- European Materials Research Society (E-MRS) 2011 Spring Meeting, May 2011, English, Europian Materials Research Society, Acropolis Congress Center, Nice, France, International conferenceNonlinear optical properties of P- or B-doped Si nanocrystals
Poster presentation
- European Materials Research Society (E-MRS) 2011 Spring Meeting, May 2011, English, Europian Materials Research Society, Acropolis Congress Center, Nice, France, International conferenceBroadband near-infrared emission of Bismuth ions sensitized by Silicon nanocrystals
Poster presentation
- Materials Research Society 2011 Spring Meeting, Apr. 2011, English, Materials Research Society, San Francisco, USA, International conferenceEfficient near-infrared luminescence and energy transfer in Nd-Bi codoped zeolites
Oral presentation
- ナノ構造・物性 第3回研究会, Mar. 2011, Japanese, 神戸市, Domestic conference有機ナノワイヤ配向膜に誘起された表面プラズモンの異方性伝搬
Oral presentation
- 2011年春季 第58回 応用物理学関係連合講演会, Mar. 2011, Japanese, 応用物理学会, 厚木市, Domestic conference表面プラズモンにより励起した単一Si量子ドットの発光特性
Oral presentation
- 2011年春季 第58回 応用物理学関係連合講演会, Mar. 2011, Japanese, 応用物理学会, 厚木市, Domestic conference紫外光用サブ波長構造トゥルーゼロオーダー波長板
Oral presentation
- ナノ構造・物性 第3回研究会, Mar. 2011, Japanese, 神戸市, Domestic conference金属-誘電体-金属構造における励起子-表面プラズモン相互作用
Oral presentation
- 2011年春季 第58回 応用物理学関係連合講演会, Mar. 2011, Japanese, 応用物理学会, 厚木市, Domestic conference金ナノロッドによるEr イオンのアップコンバージョン発光の増強
Oral presentation
- 2011年春季 第58回 応用物理学関係連合講演会, Mar. 2011, Japanese, 応用物理学会, 厚木市, Domestic conferenceSiナノ結晶とBiイオンを同時ドープしたSiO2 薄膜の広帯域近赤外発光
Oral presentation
- 2011年春季 第58回 応用物理学関係連合講演会, Mar. 2011, Japanese, 応用物理学会, 厚木市, Domestic conferenceP,B同時ドープSiナノ結晶のサイズ分布制御と発光特性
Oral presentation
- 蛍光体同学会, Feb. 2011, Japanese, 蛍光体同学会, 東京都千代田区, Domestic conferenceシリコンナノ結晶をベースとする発光材料
[Invited]
Invited oral presentation
- 若手フロンティア研究会2010, Dec. 2010, Japanese, 神戸大学研究基盤センター, 神戸大学百年記念館, Domestic conference不純物ドーピングによるシリコンナノ結晶の非線形光学特性の増大
Poster presentation
- 第20回日本MRS学術シンポジウム学術講演会, Dec. 2010, English, 横浜市, Domestic conference紫外領域で機能するポーラスシリカトゥルーゼロオーダー波長板の作製
Poster presentation
- 第20回日本MRS学術シンポジウム学術講演会, Dec. 2010, English, 横浜市, Domestic conference過剰Si添加Biドープガラス薄膜の広帯域近赤外発光
Oral presentation
- 第21回光物性研究会, Dec. 2010, Japanese, 大阪市, Domestic conference“Efficient near-infrared emission from Nd-Bi codoped zeolites
Poster presentation
- 第21回光物性研究会, Dec. 2010, Japanese, 大阪市, Domestic conferenceポーラスシリカ紫外光用トゥルーゼロオーダー波長板
Poster presentation
- 第21回光物性研究会, Dec. 2010, Japanese, 光物性研究会, 大阪市立大学 学術情報総合センター, Domestic conferencePドーピングによるSiナノ結晶の3次の非線形光学応答の増大とそのメカニズムに関する研究
Poster presentation
- Workshop on Information, Nano and Photonics Technology 2010 (WINP Tech 2010), Dec. 2010, English, 神戸市, Domestic conferencePhotoluminescence from n-type and p-type impurity co-doped Si nanocrystal/borophosilicate glass multilayer film
Poster presentation
- 第20回日本MRS学術シンポジウム学術講演会, Dec. 2010, English, 横浜市, Domestic conferenceP,B同時ドープSiナノ結晶/BPSG多層膜の発光特性
Poster presentation
- 第21回光物性研究会, Dec. 2010, Japanese, 大阪市, Domestic conferencen型不純物とp型不純物を同時ドーピングしたSiナノ結晶の発光特性
Poster presentation
- 第20回日本MRS学術シンポジウム学術講演会, Dec. 2010, English, 横浜市, Domestic conferenceEnhancement of the nonlinear optical properties of Si nanocrystals by impurity-doping
Poster presentation
- 第20回日本MRS学術シンポジウム学術講演会, Dec. 2010, English, 横浜市, Domestic conferenceEnhancement of the nonlinear optical
Poster presentation
- Workshop on Information, Nano and Photonics Technology 2010 (WINP Tech 2010), Dec. 2010, English, 神戸市, Domestic conferenceEnhancement of near-infrared luminescence from neodymium in zeolites by codoping bismuth
Poster presentation
- 第21回光物性研究会, Dec. 2010, Japanese, 大阪市, Domestic conferenceEfficient near-infrared emission from Nd-Bi codoped zeolites
Poster presentation
- Workshop on Information, Nano and Photonics Technology 2010 (WINP Tech 2010), Dec. 2010, English, 神戸市, Domestic conferenceBroadband near-infrared photoluminescence in Bi-doped SiOx films
Poster presentation
- 第21回光物性研究会, Dec. 2010, Japanese, 大阪市, Domestic conferenceBiドープ過剰 Si添加SiO2薄膜の近赤外発光
Poster presentation
- Workshop on Information, Nano and Photonics Technology 2010 (WINP Tech 2010), Dec. 2010, English, 神戸市, Domestic conferenceBirefringent porous silica true zero-order wave plate operating in the ultraviolet range
Poster presentation
- 励起ナノプロセス研究会 第6回研究会, Nov. 2010, Japanese, 堺市, Domestic conferenceSi ナノ結晶からのエネルギー移動による希土類イオンの励起
[Invited]
Invited oral presentation
- 3rd International Congress on Ceramics, Nov. 2010, English, 大阪市, International conferenceHighly Fluorescent Bismuth Doped Aluminosilicate/Silica Core-Shell Nanoparticles for Multifunctional Near Infrared Bioimaging
Oral presentation
- The 6th International Workshop on Nano-scale Spectroscopy and Nanotechnology, Oct. 2010, English, 神戸市, International conferenceEnhanced Fluorescence of Dye Layers on Nonmetallic Nanoparticles
Poster presentation
- 第71回応用物理学会学術講演会, Sep. 2010, Japanese, 応用物理学会, 長崎市, Domestic conference近赤外発光センタードープナノ構造
[Invited]
Invited oral presentation
- 第71回応用物理学会学術講演会, Sep. 2010, Japanese, 応用物理学会, 長崎大学文教キャンパス, Domestic conferenceSiナノ結晶の非線形光学特性(III) -不純物ドーピングの効果-
Oral presentation
- 11th IUMRS International Conference in Asia, Sep. 2010, English, Qingdao, China, International conferenceHighly Fluorescent Bismuth Doped Aluminosilicate/Silica Core-Shell Nanocomposites for Near Infrared Bioimaging
Poster presentation
- 第71回応用物理学会学術講演会, Sep. 2010, Japanese, 応用物理学会, 長崎市, Domestic conferenceEfficient near infrared emission from ytterbium by broadband sensitization of bismuth in zeolites
Oral presentation
- 第71回応用物理学会学術講演会, Sep. 2010, Japanese, 応用物理学会, 長崎市, Domestic conferenceBiドープSiOx薄膜の広帯域近赤外発光
Oral presentation
- 14th International Symposium on Ultrafast Phenomena in Semiconductors (14th UFPS), Aug. 2010, English, Vilnius, Lithuania, International conferenceOptical Properties of Intrinsic and Impurity-Doped Silicon Nanocrystals
[Invited]
Invited oral presentation
- 11th International Conference on Near-field Optics, Nanophotonics & Related Techniques, Aug. 2010, English, Beijing, China, International conferenceFluorescence enhancement caused by nonmetallic particles
Poster presentation
- KJF 2010 International Conference on Organic Materials for Electronics and Photonics, Aug. 2010, English, 北九州市, International conferenceEnhanced light emission from an organic emitting layer embedded in metal-insulator-metal structures
Poster presentation
- 11th International Conference on Near-field Optics, Nanophotonics & Related Techniques, Aug. 2010, English, Beijing, China, International conferenceAnisotropic Propagation of Surface Plasmon Polaritons Induced by Oriented Molecular Over Layers
Poster presentation
- European Materials Research Society (E-MRS) 2010 Spring Meeting, Jun. 2010, English, Strasbourg, International conferenceNonlinear Optical Properties of Impurity Doped Si Nanocrystals
[Invited]
Invited oral presentation
- ナノ学会第8回大会, May 2010, Japanese, ナノ学会, 岡崎市, Domestic conference銀微粒子に吸着したポリインのPVAコンポジット膜の作製
Oral presentation
- ナノ学会第8回大会, May 2010, Japanese, ナノ学会, 岡崎市, Domestic conferenceSi微粒子による有機色素の蛍光増強
Oral presentation
- The International Conference on NANOPHOTONICS 2010, May 2010, English, つくば市, International conferenceOptical property of erbium/bismuth codoped zeolites
Oral presentation
- The International Conference on NANOPHOTONICS 2010, May 2010, English, つくば市, International conferenceAnisotropic propagation of Surface Plasmon Polaritons Caused by Organic Nanowire Layers
Oral presentation
- 2010 MRS Spring Meeting, Apr. 2010, English, San Francisco, USA, International conferenceOptical Properties of Impurity Doped Si Nanocrystals
[Invited]
Invited oral presentation
- 2010年春季 第57回 応用物理学会関係連合講演会, Mar. 2010, Japanese, 応用物理学会, 平塚市, Domestic conference面プラズモン励起によるシリコンナノ結晶の発光増強
[Invited]
Invited oral presentation
- 2010年春季 第57回 応用物理学会関係連合講演会, Mar. 2010, Japanese, 応用物理学会, 平塚市, Domestic conferenceSPP異方性伝播による有機ナノワイヤの配向性評価
Poster presentation
- 2010年春季 第57回 応用物理学会関係連合講演会, Mar. 2010, Japanese, 応用物理学会, 平塚市, Domestic conferenceSiナノ結晶の非線形光学特性(II) -Pドーピングによる効果-
Poster presentation
- 2010年春季 第57回 応用物理学会関係連合講演会, Mar. 2010, Japanese, 応用物理学会, 平塚市, Domestic conferenceMIM構造中に埋め込まれた有機色素の発光増強
Poster presentation
- 物性研短期研究会 「顕微分光とナノサイエンスの発展」, Feb. 2010, Japanese, 柏市, Domestic conference顕微ラマン分光法によるシリコンナノワイヤーの不純物分布評価
[Invited]
Invited oral presentation
- 第14 回 <けいはんな>新産業創出交流センター シーズフォーラム, Jan. 2010, Japanese, 大阪市, Domestic conferenceシリコン近赤外光学素子
[Invited]
Invited oral presentation
- 「ナノ構造・物性部会」第2回研究会, Jan. 2010, Japanese, ナノ学会, 神戸市, Domestic conferenceSPP異方性伝播による有機ナノワイヤの配向性評価
Oral presentation
- 若手フロンティア研究会2009, Dec. 2009, Japanese, 神戸市, Domestic conference面内に高屈折異方性を有するポーラスシリコンにおける深さ方向の屈折率異方性評価
Poster presentation
- 第19回 日本MRS学術シンポジウム, Dec. 2009, English, 横浜市, Domestic conference複屈折性ポーラスシリコンにおける深さ方向の屈折率評価|Investigation of refractive index in the thickness direction of birefringent porous silicon
Poster presentation
- 第19回 日本MRS学術シンポジウム, Dec. 2009, English, 横浜市, Domestic conference単一P-type/intrinsic シリコンナノワイヤ中の活性不純物分布の評価|Distribution of electricallyactive impurities in single P-type/intrinsic silicon nanowires
Oral presentation
- 若手フロンティア研究会2009, Dec. 2009, Japanese, 神戸市, Domestic conferenceラマン散乱によるP型半導体ナノワイヤの評価
Poster presentation
- 第19回 日本MRS学術シンポジウム, Dec. 2009, English, 横浜市, Domestic conferenceThird-order nonlinear optical propeties of Si nanocrystals embedded in SiO2 prepared by a cosputtering method
Poster presentation
- Workshop on Information, Nano and photonics Technology 2009 (WINP Tech 2009), Dec. 2009, English, 神戸市, Domestic conferenceThird-order nonlinear optical properties of Si nanocrystals
Poster presentation
- 第20回 光物性研究会, Dec. 2009, English, 大阪市, Domestic conferenceSuperbroadband near infrared emission from bismuth doped high-silica nanocrystalline zeolites
Poster presentation
- 若手フロンティア研究会2009, Dec. 2009, Japanese, 神戸市, Domestic conferenceSiクラスターをドープしたSiO2薄膜の非線形光学特性
Poster presentation
- 第20回 光物性研究会, Dec. 2009, Japanese, 大阪市, Domestic conferencePドープシリコンナノ結晶の三次非線形光学特性
Poster presentation
- 第19回 日本MRS学術シンポジウム, Dec. 2009, English, 横浜市, Domestic conferencePreparation and luminescence properties of erbium/bismuth codoped zeolites
Oral presentation
- Workshop on Information, Nano and photonics Technology 2009 (WINP Tech 2009), Dec. 2009, English, 神戸市, Domestic conferenceNear-infrared photoluminescence in Bi-doped-glass/Si-nanocrystals multilayer film
Poster presentation
- Workshop on Information, Nano and photonics Technology 2009 (WINP Tech 2009), Dec. 2009, English, 神戸市, Domestic conferenceIn-plane and depth direction refractive indices of birefringent porous silicon
Poster presentation
- Workshop on Information, Nano and photonics Technology 2009 (WINP Tech 2009), Dec. 2009, English, 神戸市, Domestic conferenceBoron Distribution in in-situ Boron-doped Individual Si Nanowires Grown by a Vapor Liquid Solid Process
Poster presentation
- 第19回 日本MRS学術シンポジウム, Dec. 2009, English, 横浜市, Domestic conferenceBi ドープガラス/Si ナノ結晶多層膜の広帯域近赤外発光
Poster presentation
- 第20回 光物性研究会, Dec. 2009, Japanese, 大阪市, Domestic conferenceBiドープガラス/Siナノ結晶多層膜の広帯域近赤外発光
Poster presentation
- 第12回 シリコンフォトニクス研究会, Nov. 2009, Japanese, 電子情報通信学会, 東京都文京区, Domestic conference不純物ドープシリコンナノ結晶の三次非線形光学特性
Poster presentation
- The 7th Asia-Pacific Conference on Near-Field Optics, Nov. 2009, English, Jeju Island, Korea, International conferenceSurface-Enhanced Raman Scattering of Size-Selected Polyynes (C8H2) Adsorbed on Silver Particles
Poster presentation
- The 7th Asia-Pacific Conference on Near-Field Optics, Nov. 2009, English, Jeju Island, Korea, International conferenceQuenching-Free Fluorescence Enhancement Caused by Nonmetallic Small Particles: Rhodamine B on GaP Particle Layers
Oral presentation
- 第12回 シリコンフォトニクス研究会, Nov. 2009, Japanese, 電子情報通信学会, 東京都文京区, Domestic conferenceBiドープガラス/Siナノ結晶多層膜の広帯域近赤外発光
Poster presentation
- 216th ECS Meeting, Oct. 2009, English, Vienna, Austria, International conferenceControlling the degree of the optical anisotropy of birefringent porous silicon
Oral presentation
- 2009年秋季 第70回 応用物理学会 学術講演会, Sep. 2009, Japanese, 応用物理学会, 富山市, Domestic conference複屈折性ポーラスシリコンにおける面内及び深さ方向の光学異方性評価
Poster presentation
- 2009年秋季 第70回 応用物理学会 学術講演会, Sep. 2009, Japanese, 応用物理学会, 富山市, Domestic conference不純物ドープSiナノ結晶
[Invited]
Invited oral presentation
- 2009年秋季 第70回 応用物理学会 学術講演会, Sep. 2009, Japanese, 応用物理学会, 富山市, Domestic conferenceラマン散乱による p-type/intrinsic, intrinsic/p-type Si ナノワイヤの評価(II)
Poster presentation
- International conference on nanoscience and technology, Sep. 2009, English, ChinaNANO 2009, Beijing, China, International conferenceSuperbroadband Near-Infrared Emission from Bismuth Embedded Zeolites and Their Derivatives
Oral presentation
- 2009年秋季 第70回 応用物理学会 学術講演会, Sep. 2009, Japanese, 応用物理学会, 富山市, Domestic conferenceSiナノ結晶、Er共添加SiO2薄膜におけるEr3+の励起断面積
Poster presentation
- 2009年秋季 第70回 応用物理学会 学術講演会, Sep. 2009, Japanese, 応用物理学会, 富山市, Domestic conferenceSiナノ結晶の非線形光学特性(I)
Poster presentation
- 2009年秋季 第70回 応用物理学会 学術講演会, Sep. 2009, Japanese, 応用物理学会, 富山市, Domestic conferenceBi doped glass/SiOx多層膜の広帯域近赤外発光
Poster presentation
- “Trends in Nanotechnology” (TNT2009), Sep. 2009, English, Barcelona, Spain, International conferenceA General Route to Efficient Near-Infrared Emission of Optically Active Nanozeolites
Oral presentation
- 静岡大学電子工学研究所 招待講演会, Aug. 2009, Japanese, 静岡大学電子工学研究所, 浜松市, Domestic conferenceシリコンナノ構造からの発光:ドーパントの効果
[Invited]
Invited oral presentation
- CECAM Workshop “Dopants and Impurities in Semiconducting Nanowires”, Jul. 2009, English, Ecole Polytechnique Fédérale de Lausanne (EPFL), and Centre Européen de Calcul Atomique et Moléculaire (CECAM), Lausanne, Switerland, International conferenceRaman Characterization of p-type Impurities in Individual Silicon and Silicon Germanium Nanowires
[Invited]
Invited oral presentation
- 24th International Conference on Defects in Semiconductors (ICDS-24), Jul. 2009, English, St. Petersburg, Russia, International conferenceImpurity Doping in Silicon Nanowires and Nanocrystals
[Invited]
Invited oral presentation
- The 14th International Conference on Modulated Semiconductor Structures, Jul. 2009, English, 神戸市, International conferenceBoron and Germanium Distribution in Individual Boron-doped Si1-xGex Alloy Nanowires Grown by a Vapor Liquid Solid process
Oral presentation
- Fourth International Conference on Surface Plasmon Photonics SPP4, Jun. 2009, English, Amsterdam, the Netherlands, International conferenceEnhanced Light Emision Mediated by Radiative Surface Plasmons in Metal-Insulator-Metal Structures
Oral presentation
- Fourth International Conference on Surface Plasmon Photonics SPP4, Jun. 2009, English, Amsterdam, the Netherlands, International conferenceAnisotropic propagation of surface plasmon polaritons caused by oriented molecular overlayer
Poster presentation
- ナノ学会第7回大会, May 2009, Japanese, ナノ学会, 東京都文京区, Domestic conference複屈折性ポーラスシリコンの屈折率異方性制御
Poster presentation
- ナノ学会第7回大会, May 2009, Japanese, ナノ学会, 東京都文京区, Domestic conference液相中レーザーアブレーションにより作製した銀コロイドによるポリインの表面増強ラマン散乱
Poster presentation
- ナノ学会第7回大会, May 2009, Japanese, ナノ学会, 東京都文京区, Domestic conferenceAnisotropic propagation of surface plasmon polaritons caused by oriented molecular overlayer
Poster presentation
- 春季第56回応用物理学会関係連合講演会, Mar. 2009, Japanese, 応用物理学会, つくば市, Domestic conference複屈折性ポーラスシリコンで作製した波長板の特性制御
Oral presentation
- 春季第56回応用物理学会関係連合講演会, Mar. 2009, Japanese, 応用物理学会, つくば市, Domestic conference銀アイランド膜の表面プラズモン励起によるEr、Ybを共添加したナノ粒子のアップコンバージョン発光増強
Oral presentation
- 第7回プラズモニクスシンポジウム, Mar. 2009, Japanese, プラズモニクス研究会, 徳島県, Domestic conference金属/誘電体/金属構造に埋め込まれた有機色素の発光増強メカニズム
Oral presentation
- 春季第56回応用物理学会関係連合講演会, Mar. 2009, Japanese, 応用物理学会, つくば市, Domestic conferenceラマン散乱による単一BドープSi1-xGexナノワイヤーの評価
Poster presentation
- 春季第56回応用物理学会関係連合講演会, Mar. 2009, Japanese, 応用物理学会, つくば市, Domestic conferenceNi2+ doped glass ceramics/Si多層膜の広帯域近赤外発光
Poster presentation
- 第7回プラズモニクスシンポジウム, Mar. 2009, English, プラズモニクス研究会, 徳島県, Domestic conferenceAnisotropic Propagation of Surface Plasmon Polaritons Caused by Oriented Molecular Overlayer
Oral presentation
- 若手フロンティア研究会2008, Dec. 2008, Japanese, 神戸大学, 神戸市, Domestic conference金属ナノ構造の表面プラズモン励起によるシリコンナノ結晶の発光増強
Poster presentation
- Marerial Research Society 2008 Fall Meeting, Dec. 2008, English, Materials Research Society (MRS), Boston, USA, International conferenceRaman Characterization of Active Impurities in Single Boron-doped Si1-xGex Alloy Nanowires
Oral presentation
- 2008 MRS Fall Meeting, Dec. 2008, English, MRS, Boston, USA, International conferenceErbium silicate nanorods: promising building blocks for optical devices
Oral presentation
- Marerial Research Society 2008 Fall Meeting, Dec. 2008, English, Materials Research Society (MRS), Boston, USA, International conferenceDistribution of active impurities in single silicon nanowire
Oral presentation
- Materials Research Society 2008 Fall Meeting, Dec. 2008, English, Materials Research Society (MRS), Boston, USA, International conferenceDichroic Rugate Filters Based on Birefringent Porous Silicon
Oral presentation
- Workshop on Information, Nano and photonics Technology 2008, Nov. 2008, English, 神戸大学, 神戸市, Domestic conferenceRaman characterization of electrically-active impurities in boron-doped silicon nanowire
Poster presentation
- Workshop on Information, Nano and photonics Technology 2008, Nov. 2008, English, 神戸大学, 神戸市, Domestic conferenceEnhancement of luminescence from silicon nanocrystals via coupling to surface plasmon
Poster presentation
- Workshop on Information, Nano and photonics Technology 2008, Nov. 2008, English, 神戸大学, 神戸市, Domestic conferenceDichroic Rugate Filters Based on Birefringent Porous Silicon
Poster presentation
- 214th ECS Meeting, Oct. 2008, English, ECS, Honolulu, USA, International conferenceDesign and Fabrication of Extended-Bandwidth Rugate Filters Made of Porous Silicon
Oral presentation
- 第69回応用物理学会学術講演会, Sep. 2008, Japanese, 応用物理学会, 名古屋市, Domestic conference複屈折性ポーラスシリコンを用いたダイクロイック・ルゲートフィルター
Oral presentation
- 第69回応用物理学会学術講演会, Sep. 2008, Japanese, 応用物理学会, 名古屋市, Domestic conference表面プラズモン励起によるSiナノ結晶の発光増強
Oral presentation
- 第69回応用物理学会学術講演会, Sep. 2008, Japanese, 応用物理学会, 名古屋市, Domestic conferenceラマン散乱による単一Si1-xGexナノワイヤーの評価
Oral presentation
- 第69回応用物理学会学術講演会, Sep. 2008, Japanese, 応用物理学会, 名古屋市, Domestic conferenceRaman散乱によるp-type/intrinsic , intrinsic/p-type Siナノワイヤ中のドーピングプロファイルの評価
Oral presentation
- The fifth international workshop on Active-Matrix FlatPanel Displays and Devices (AM-FPD 08) -TFT Technologies and FPD Materials, Jul. 2008, English, 不明, 東京都, International conferenceOptical Properties of Si Nanocrystals
Invited oral presentation
- The 15th International Conference on Luminescence and Otical Spectroscopy of Condensed Matter, Jul. 2008, English, Laboratoire Physico-Chimie des Materiaux Luminescents, Unicersite Claude Bernard Lyon 1, Centre National de la Recherche Scientifique, Unicersite de Lyon, Lyon, France, International conferenceEnhanced Photoluminescence from Dye Layers Embedded in Metal-Insulator-Metal Structures
Poster presentation
- E-MRS 2008 Spring Meeting, May 2008, English, Materials Research Society (MRS), Strasbourg, France, International conferenceRaman characterization of electrically-active impurities in boron-doped silicon nanowire
Oral presentation
- E-MRS 2008 Spring Meeting, May 2008, English, Materials Research Society (MRS), Strasbourg, France, International conferencePhotoluminescence and electron spin resonance studies of impurity compensated silicon nanocrystals
Oral presentation
- ナノ学会第6回大会, May 2008, Japanese, ナノ学会, 福岡市, Domestic conferenceMIM構造に埋め込まれた色素の発光増強
Poster presentation
- SEDWAL (Sensitized Er doped waveguide amplifier/laser) Workshop 2008, Apr. 2008, English, 不明, Levico Terme - Trento,Italy, International conferenceModification of luminescence properties of Er doped Si nanocrystals near a metal thin film
Invited oral presentation
- 春季第55回応用物理学会関係連合講演会, Mar. 2008, Japanese, 応用物理学会, 千葉県, Domestic conferenceVLS法によるSi1-xGexナノワイヤーの成長機構
Oral presentation
- 春季第55回応用物理学会関係連合講演会, Mar. 2008, Japanese, 応用物理学会, 千葉県, Domestic conferenceVLS法により成長したBドープSiナノワイヤーのB濃度分布
Oral presentation
- 春季第55回応用物理学会関係連合講演会, Mar. 2008, Japanese, 応用物理学会, 千葉県, Domestic conferenceMIM構造中に埋め込まれた色素の発光特性II
Oral presentation
- 電気情報通信学会シリコン材料・デバイス研究会(SDM), Dec. 2007, Japanese, 電気情報通信学会, 奈良県, Domestic conferenceシリコンナノ結晶の物性と応用
Invited oral presentation
- 第18回光物性研究会, Dec. 2007, Japanese, 光物性研究会, 大阪府, Domestic conferenceSiナノ結晶からErへのエネルギー移動レートの分布解析
Poster presentation
- 第18回日本MRS学術シンポジウム, Dec. 2007, Japanese, 日本MRS, 東京都, Domestic conferenceSensitized Generation of Singlet Oxygen by Allylamine-Terminated Hydrophilic Porous Si
Poster presentation
- 第18回日本MRS学術シンポジウム, Dec. 2007, Japanese, 日本MRS, 東京都, Domestic conferenceroughnessを持つ金薄膜近傍におけるSiナノ結晶の発光特性
Poster presentation
- 若手フロンティア研究会2007, Dec. 2007, Japanese, 神戸大学, 神戸市, Domestic conferenceMIM構造中に埋め込まれた色素の発光特性
Poster presentation
- 若手フロンティア研究会2007, Dec. 2007, Japanese, 神戸大学, 神戸市, Domestic conferenceMIM構造のモードを利用した色素の発光増強
Poster presentation
- 若手フロンティア研究会2007, Dec. 2007, English, 神戸大学, 神戸市, Domestic conferenceEffects of molecular orientation on surface plasmon-coupled emission patterns
Poster presentation
- 2007 Materials Research Society (MRS) fall meeting, Nov. 2007, English, Materials Research Society (MRS), Boston,USA, International conferencePhotoluminescence Properties of Silicon Nanocrystals near a Metal Thin Film
Invited oral presentation
- 第68回応用物理学会学術講演会, Sep. 2007, Japanese, 応用物理学会, 北海道, Domestic conference有機色素を吸着させたポーラスシリコンによる一重項酸素生成
Oral presentation
- 第68回応用物理学会学術講演会, Sep. 2007, Japanese, 応用物理学会, 北海道, Domestic conference表面プラズモン励起によるEr3+のアップコンバージョン発光の増強
Oral presentation
- 第68回応用物理学会学術講演会, Sep. 2007, Japanese, 応用物理学会, 北海道, Domestic conference最大エントロピー法による半導体ナノ結晶の発光減衰曲線解析
Oral presentation
- 第68回応用物理学会学術講演会, Sep. 2007, Japanese, 応用物理学会, 北海道, Domestic conferenceラマン散乱によるBドープSiナノワイヤのドーピング濃度評価
Oral presentation
- 第68回応用物理学会学術講演会, Sep. 2007, Japanese, 応用物理学会, 北海道, Domestic conferenceポーラスシリコンを用いた広帯域ルゲートフィルター
Oral presentation
- 第68回応用物理学会学術講演会, Sep. 2007, Japanese, 応用物理学会, 北海道, Domestic conferenceP,BをドーピングしたSiナノ結晶の電子スピン共鳴
Oral presentation
- 第68回応用物理学会学術講演会, Sep. 2007, Japanese, 応用物理学会, 北海道, Domestic conferenceMIM構造中に埋め込まれた色素の発光特性
Oral presentation
- ナノオプティクス研究グループ第16回研究討論会, Jul. 2007, Japanese, ナノオプティクス研究グループ, 神戸市, Domestic conference表面プラズモンポラリトン励起によるシリコンナノ結晶の発光増強
Invited oral presentation
- 神戸大学連携創造本部先端研究推進部門2007年度第5回ナノ・フォトニクス技術セミナー, Jul. 2007, Japanese, 神戸大学連携創造本部先端研究推進部門, 神戸市, Domestic conference金属薄膜近傍におけるシリコンナノ結晶の発光特性
Others
- Third International Conference on Surface Plasmon Photonics SPP3, Jun. 2007, English, Dijon,France, International conferenceEffects of molecular orientation on surface plasmon-coupled emission patterns
Poster presentation
- ナノ学会第5回大会, May 2007, English, ナノ学会, つくば市, Domestic conference配向分子による表面プラズモン励起発光
Poster presentation
- 第54回応用物理学関係連合講演会, Mar. 2007, English, 応用物理学会, 青山学院大学, International conference表面修飾したポーラスSiからの酸素分子へのエネルギー移動による一重項酸素の生成
[Invited]
Invited oral presentation
- 第54回応用物理学関係連合講演会, Mar. 2007, English, 応用物理学会, 青山学院大学, International conference表面プラズモンポラリトン励起によるSiナノ結晶の発光増強
[Invited]
Invited oral presentation
- 量子エレクトロニクス研究会「シリコンフォトニクス」, Jan. 2007, English, 上智大学軽井沢セミナーハウス, International conference希土類ドープシリコンナノ結晶
[Invited]
Invited oral presentation
- 第17回光物性研究会, Dec. 2006, English, 光物性研究会, 大阪市立大学, International conferenceSiナノ結晶の発光量子効率
[Invited]
Invited oral presentation
- 第17回日本MRS学術シンポジウム, Dec. 2006, English, 日本大学, International conferenceMeasurement of the Quantum Efficiency of Silicon Nanocrystals through a Controlled Photonic Mode Density
[Invited]
Invited oral presentation
- 2nd Workshop on “Impurity Based Electroluminescent Devices and Materials,”, Oct. 2006, English, Wakayama, Japan, International conferencePhotoluminescence Properties of Impurity-doped Si Nanocrystals
[Invited]
Invited oral presentation
- 日本物理学会2006年秋季大会, Sep. 2006, English, 日本物理学会, 千葉大学, International conference金薄膜近傍におけるErイオンのアップコンバージョン発光の増強に関する研究
[Invited]
Invited oral presentation
- 日本物理学会2006年秋季大会, Sep. 2006, English, 応用物理学会, 千葉大学, International conferenceSiナノ結晶の発光量子効率
[Invited]
Invited oral presentation
- 9th International Conference on Near-field Optics, Sep. 2006, English, Lausanne Swiss,, International conferenceEnhancement of energy transfer rate by surface plasmons in Ag islands film
[Invited]
Invited oral presentation
- 第67回応用物理学関係連合講演会, Aug. 2006, English, 応用物理学会, 立命館大学(びわこ・くさつキャンパス), International conference水中におけるポーラスSiからのエネルギー移動による一重項酸素生成
[Invited]
Invited oral presentation
- 第67回応用物理学関係連合講演会, Aug. 2006, English, 応用物理学会, 立命館大学(びわこ・くさつキャンパス), International conference金薄膜近傍におけるErのアップコンバージョン発光増強
[Invited]
Invited oral presentation
- 第67回応用物理学関係連合講演会, Aug. 2006, English, 応用物理学会, 立命館大学(びわこ・くさつキャンパス), International conferenceシリコンナノ結晶の発光特性と光増感作用
[Invited]
Invited oral presentation
- Tsukuba Satellite Symposium on Single Molecule and Tip-enhanced Raman Scattering, Aug. 2006, English, Tsukuba, Japan, International conferenceVibrational properties of hydrogen-capped polyyne: Normal Raman and surface-enhanced Raman study
[Invited]
Invited oral presentation
- 第67回応用物理学関係連合講演会, Aug. 2006, English, 応用物理学会, 立命館大学(びわこ・くさつキャンパス), International conferencePをドーピングしたSi ナノ結晶の電子スピン共鳴
[Invited]
Invited oral presentation
- JSTナノテクノロジー分野別バーチャルラボ成果報告会, Jul. 2006, Japanese, JST, 東京国際フォーラム, Domestic conference光増幅素子作製のためのSiナノ結晶・Er共添加石英膜の光導波特性
Poster presentation
- 13th International Symposium on Small Particles and Inorganic Clusters (ISSPIC13), Jul. 2006, English, Goteborg, Sweden, International conferenceVibrational properties of hydrogen-capped polyyne: Normal Raman and surface-enhanced Raman study
[Invited]
Invited oral presentation
- 13th International Symposium on Small Particles and Inorganic Clusters (ISSPIC13), Jul. 2006, English, Goteborg, Sweden, International conferenceProduction and Characterization of Hydrogen-Capped Linear Carbon Molecules
[Invited]
Invited oral presentation
- International Workshop on Nanostructured Materials (Nanomat), Jun. 2006, English, Antalya, Turkey, International conferenceModification of luminescence properties of Er doped Si nanocrystals near a metal thin film
[Invited]
Invited oral presentation
- ナノ学会第4回大会, May 2006, English, ナノ学会, 神戸市, International conference水中におけるポーラスSiを光増感剤とした一重項酸素の生成
[Invited]
Invited oral presentation
- European Material Research Society 2006 Spring Meeting, May 2006, English, Nice, France, International conferenceSize dependence of photoluminescence quantum efficiency of Si nanocrystals
[Invited]
Invited oral presentation
- ナノ学会第4回大会, May 2006, English, ナノ学会, 神戸市, International conferencePをドーピングしたSiナノ結晶の電子スピン共鳴
[Invited]
Invited oral presentation
- European Material Research Society 2006 Spring Meeting, May 2006, English, Nice, France, International conferenceModification of the energy transfer from Si nanocrystals to Er ions near a Au layer wavelength dependence
[Invited]
Invited oral presentation
- 2006 MRS spring meeting, Symposium I “Silicon-Based Microphotonics,” I2., Apr. 2006, English, San Francisco, USA, International conferenceSilicon Dioxide Films Containing Silicon Nanocrystals and Er ions Modification of Spontaneous Emission Rate and Energy Transfer Rate by Metal Thin Films
[Invited]
Invited oral presentation
- 第53回応用物理学関係連合講演会, Mar. 2006, Japanese, 武蔵工業大学, Domestic conference貴金属ナノ粒子が埋め込まれた磁性ガーネット膜の分光エリプソメトリー
Oral presentation
- 日本物理学会第61回年次大会, Mar. 2006, Japanese, 愛媛大学・松山大学, Domestic conference貴金属ナノコンポジット膜の分光エリプソメトリー
Oral presentation
- 第53回応用物理学関係連合講演会, Mar. 2006, Japanese, 武蔵工業大学, Domestic conferenceSiナノ結晶増感Erエミッタ
Invited oral presentation
- 第53回応用物理学関係連合講演会, Mar. 2006, Japanese, 武蔵工業大学, Domestic conferenceSiナノ結晶の発光量子効率
Oral presentation
- Porous Semiconductors Science and Technology, 5th International Conference, Mar. 2006, English, Sitges-Barcelona ,Spain, International conferenceSinglet oxygen formation by porous silicon in solution
Oral presentation
- Porous Semiconductors-Science and Technology, 5th International Conference, Mar. 2006, English, Sitges-Barcelona ,Spain, International conferenceForm birefringence of anisotropically nanostructured silicon
Oral presentation
- 電子情報通信学会研究会 レーザ・量子エレクトロニクス研究会, Jan. 2006, Japanese, 電子情報通信学会, 神戸大学, Domestic conferenceSi・Erを共添加したSiO2膜の導波路型光増幅器への応用
Oral presentation
- 1st Workshop on Doping of Semiconductor Nanostructures, Jan. 2006, English, Washington DC, USA, International conferenceOptical Properties of Impurity-doped Si Nanocrystals
Invited oral presentation
- 第16回光物性研究会, Dec. 2005, Japanese, 大阪市立大学, Domestic conference不純物をドープしたSiナノ結晶のフォトルミネッセンスと電子スピン共鳴
Poster presentation
- Materials Research Society 2005 fall meeting, Nov. 2005, English, Hynes Convention Ctr., Boston, MA, USA, International conferenceTime-resolved Photoluminescence Studies of Energy Transfer from Excitons in Si Nanocrystals to Oxygen Molecules
Oral presentation
- Materials Research Society 2005 fall meeting, Nov. 2005, English, Boston, MA, USA, International conferenceManeto-Optical Kerr Effects of Magnetic Garnet Thin Films Incorporating Gold Nanoparticles: A Possible Coupling between Localized Surface Plasmons and Magnetio-Optical Effects
Oral presentation
- Materials Research Society 2005 fall meeting, Nov. 2005, English, Boston, MA, USA, International conferenceEnhancement of Radiative Recombination Rate of Excitons in Si Nanocrystals on Au Thin Films
Oral presentation
- The 5th Asia-Pacific Conference on Near-field Optics, Nov. 2005, English, Niigata, Japan, International conferenceEnhancement of photoluminescence form Yb and Er co-doped Al2O3 films by an asymmetric metal cavity
Poster presentation
- Materials Research Society 2005 fall meeting, Nov. 2005, English, Boston, MA, USA, International conferenceEnhancement of 1.54 μm Emission from Er and Yb co-doped Al2O3 Films by Au Thin Film
Oral presentation
- 応物学会講演会, Sep. 2005, Japanese, 応用物理学会, 徳島大学, Domestic conference平面導波路型光アンプ開発のための光導波損失評価
Poster presentation
- 次世代シーズ懇話会 第2回 ナノテクノロジー・材料分野, Sep. 2005, Japanese, NEDO技術開発機構 ナノテクノロジー・材料技術開発部, 川崎日航ホテル, Domestic conferenceSiナノ結晶をベースとする一重項酸素発生光増感剤の開発－発生メカニズムの解明及び、化学、生物、食品分野への応用の探求－
Oral presentation
- 第66回応用物理学会学術講演会, Sep. 2005, Japanese, 徳島大学, Domestic conferenceAu薄膜によるEr、Yb同時ドープAl2O3薄膜の発光増強
Oral presentation
- International Conference on Defects in Semiconductors, Jul. 2005, English, Awaji-island, Japan, International conferenceOptical properties of Si nanocrystals embedded in SiOxNy thin film
Oral presentation
- ナノ学会第3回大会, May 2005, Japanese, 仙台市民会館, Domestic conference不純物をドープしたSiナノ結晶の発光特性
Poster presentation
- ナノ学会第3回大会, May 2005, Japanese, 仙台市民会館, Domestic conference水中レーザー照射によるフラーレン水溶性コロイド溶液の調製
Oral presentation
- The 10th International Conference on New Diamond Science and Technology, May 2005, English, Tsukuba, Japan, International conferenceSynthesis of polyynes by laser ablation of diamond nanoparticles suspended in solution
Oral presentation
- Surface Plasmon Photonics 2, May 2005, English, Graz, Austria, International conferenceEnergy transfer from Si nanocrystals to Er ions near a gold surface
Oral presentation
- European Materials Research Society 2005 spring meeting, May 2005, English, Strasbourg, France, International conferenceEnergy Transfer from Si Nanocrystals to Er ions
Invited oral presentation
- 第1回シリコン・フォトニクス研究会, Apr. 2005, Japanese, 電子情報通信学会, 電気通信大学スカイオフィス, Domestic conference不純物をドープしたSiナノ結晶の発光特性
Oral presentation
- 第52回応用物理学関係連合講演会, Apr. 2005, Japanese, 埼玉大学, Domestic conferenceSiナノ結晶からErイオンへの共鳴エネルギー移動過程
Oral presentation
- 第1回シリコン・フォトニクス研究会, Apr. 2005, Japanese, 電子情報通信学会, 電気通信大学スカイオフィス, Domestic conferenceSiナノ結晶からErイオンへの共鳴エネルギー移動過程
Oral presentation
- 第1回シリコン・フォトニクス研究会, Apr. 2005, Japanese, 電子情報通信学会, 電気通信大学スカイオフィス, Domestic conferenceSiOxNy薄膜中のSiナノ結晶の発光特性
Oral presentation
- 第1回シリコン・フォトニクス研究会, Apr. 2005, Japanese, 電子情報通信学会, 電気通信大学スカイオフィス, Domestic conferenceErとSiナノ粒子を同時ドープしたSiO2薄膜へのAl添加効果
Oral presentation
- 第52回応用物理学関係連合講演会, Apr. 2005, Japanese, 埼玉大学, Domestic conferenceAlとSiとEr3+を含むSiO2薄膜の光学特性
Oral presentation
- 第52回応用物理学関係連合講演会、予稿集第3分冊 1638, Mar. 2005, Japanese, 応用物理学会, 埼玉大学, Domestic conference窒素をドーピングしたナノSi/SiO2薄膜の発光特性
Oral presentation
- 神戸大学研究活性化シンポジウム, Mar. 2005, Japanese, 神戸大学, 神戸大学, Domestic conferenceSiナノ結晶の光物性と光機能性
Oral presentation
- 第52回応用物理学関係連合講演会、予稿集第3分冊 1631, Mar. 2005, Japanese, 応用物理学会, 埼玉大学, Domestic conferenceNH3ガス処理によるErドープSiO2Sol-Gel薄膜の発光増強
Oral presentation
- 2005 MRS springl meeting,Abstract 510, Mar. 2005, Japanese, 未記入, San Fransisco,USA, International conferenceControl of energy tranfer from Si nanocrystals to Er ions by altering photonic mode density
Oral presentation
- 第52回応用物理学関係連合講演会、予稿集第3分冊 1631, Mar. 2005, Japanese, 応用物理学会, 埼玉大学, Domestic conferenceAlとSiとEr3+を含むSiO2薄膜の光学特性
Oral presentation
- 独立行政法人新エネルギー・産業技術開発機構、平成16年度研究助成事業成果報告会、予稿集 74-79, Jan. 2005, Japanese, 未記入, 東京国際フォーラム, Domestic conferenceSiナノ結晶をベースとする一重項酸素生成増感剤の開発－発生メカニズムの解明及び、科学、生物、食品分野への応用の探求
Oral presentation
- 2005 MRS springl meeting Symposium V,Abstract 510, Jan. 2005, Japanese, 未記入, San Fransisco,USA, International conferenceEnergy Exchange between Si Nanocrystals and Er ions
Oral presentation
- 第15回光物性研究会、予稿集 153, Dec. 2004, Japanese, 光物性研究会, 京都大学, Domestic conference不純物ドーピングによるSiナノ結晶の発光特性制御
Oral presentation
- 第15回光物性研究会、予稿集 349, Dec. 2004, Japanese, 光物性研究会, 京都大学, Domestic conferenceポーラスシリコンによる一重項酸素生成メカニズムに関する研究
Oral presentation
- 第15回光物性研究会、予稿集 345, Dec. 2004, Japanese, 光物性研究会, 京都大学, Domestic conferenceシリコンナノ結晶を光増感剤とした一重項酸素生成の高効率化に関する研究
Oral presentation
- 第15回日本MRS学術シンポジウム、予稿集 165, Dec. 2004, Japanese, 未記入, 日本大学, Domestic conferenceSiナノ結晶の光増感作用を利用した一重項酸素の生成
Oral presentation
- 第15回光物性研究会、予稿集 157, Dec. 2004, Japanese, 光物性研究会, 京都大学, Domestic conferenceErとSiナノ結晶を同時ドープしたSiO2薄膜の高Er濃度領域における発光特性
Oral presentation
- 第15回光物性研究会、予稿集 65, Dec. 2004, Japanese, 光物性研究会, 京都大学, Domestic conferenceAuナノ結晶によるEr3+ドープSiO2sol-gel薄膜の発光増強
Oral presentation
- 2004 MRS fall meeting Symposium F,Abstract 175, Nov. 2004, Japanese, 未記入, Boston,USA, International conferencePhotoluminescence properties of Rare-earth ions and/or Shallow impurities doped Si nanocrystals
Oral presentation
- 2004 MRS fall meeting Symposium F,Abstract 172, Nov. 2004, Japanese, 未記入, Boston,USA, International conferenceGeneration of Singlet Oxygen at Room Temperature Mediated by Enegy Tranfer from Si Nanocrystals
Oral presentation
- 2004 MRS fall meeting Symposium F "Group IV Semiconductor nanostructures",Abstract 173, Nov. 2004, Japanese, 未記入, Boston,USA, International conferenceControl of Photoluminescence Properties of Si Nanocrystals by Simultaneously Doping n and type Impurities
Oral presentation
- 12th International Symposium on Sall Prticles and Iorganic Custers(ISSPIC),Abstract A-1V-6, Sep. 2004, Japanese, 未記入, Nanjing,China, International conferenceThe mechanism of nergy transfer from Si nanovrystal to erbium ions in SiO2
Oral presentation
- 12th International Symposium on Sall Prticles and Iorganic Custers(ISSPIC),Abstract B-V11-6, Sep. 2004, Japanese, 未記入, Nanjing,China, International conferenceSynthesis of polyynes by laser ablation of diamond nanoparticles suspended in solution
Oral presentation
- 12th International Symposium on Sall Prticles and Iorganic Custers(ISSPIC),Abstract A-11-8, Sep. 2004, Japanese, 未記入, Nanjing,China, International conferenceSinglet Oxygen Formation by the Energy Transfer from Si Nanocrystals
Oral presentation
- 12th International Symposium on Sall Prticles and Iorganic Custers(ISSPIC),Abstract A-1V-5, Sep. 2004, Japanese, 未記入, Nanjing,China, International conferenceOptical properties of Er and Si-nanocrystal co-deped SiO2 films at heigh Er concentration regime
Oral presentation
- The 20th General Conference of the Condensed Matter Division European Physical Society,Abstract 157, Jul. 2004, Japanese, 未記入, Prague, International conferenceResonant Character of Raman Scattering in Single-wall Carbon nanotubes Confirmed by Photoluminescence Measurements
Oral presentation
- 第27回フラーレン・ナノチューブ総合シンポジウム、予稿集 165, Jul. 2004, Japanese, 未記入, 東京大学, Domestic conferencePreparetion of an aqueous colloidal solution of fullerenes by laser ablation in water
Oral presentation
- The 20th General Conference of the Condensed Matter Division European Physical Society,Abstract 126, Jul. 2004, Japanese, 未記入, Prague, International conferenceCurvature Influence on Carbon Nanotube Electronic Structure:Modelling and Photoluminescence Experiments
Oral presentation
- ナノ学会第２回大会、学術総合センター・一橋記念講堂、予稿集 72, May 2004, Japanese, ナノ学会, 未記入, Domestic conference高Er濃度Er/Si/SiO2混合膜の発行特性
Oral presentation
- 第19回希土類討論会, May 2004, Japanese, 未記入, 大阪大学, Domestic conferenceSiナノ結晶によるEr3+の光増感作用
Oral presentation
- E-MRS 2004 Spring Meeting A1-P1.33, May 2004, Japanese, 未記入, Strasbourg,France, International conferencePhotosensitization of Organic Moleciles by Silicon Nanocrystals
Oral presentation
- E-MRS 2004 Spring Meeting, May 2004, Japanese, 未記入, Strasbourg,France, International conferencePhotoluminescence Properties of Rare-earth lons and/or Shallow Impurity Doped Silicon Nanocrystals
Oral presentation
- E-MRS 2004 Spring Meeting A1-P1.33, May 2004, Japanese, 未記入, Strasbourg,France, International conferenceComplex Optical Diagnostics of Single-wall Carbon Nanotubes Grown and Treated by Different Techniques
Oral presentation
- 第51回応用物理学会関係連合講演会 予稿集第3分冊 p.1623, Mar. 2004, Japanese, 応用物理学会, 東京, Domestic conference同時スパッタ法によって作製したErSiO化合物の発光特性
Oral presentation
- 第51回応用物理学会関係連合講演会 予稿集第3分冊 p.1597, Mar. 2004, Japanese, 応用物理学会, 東京, Domestic conferenceSiナノ結晶（ポーラスSi）の光増感作用
Oral presentation
- 4th International Conference Porus Semiconductor Science and Technology., Mar. 2004, English, 未記入, Cullera-Valencia, Spain, International conferenceSinglet Oxygen Formation by Porus Si in Solution.(Extended abstract O-06 pp.26-27)
Oral presentation
- International Winterschools on Electronic Properties of Novel Materials(IWEPNM) IWEPNM 2004 with the title "MOLECULAR MANOSTRUCTURES", Mar. 2004, English, 未記入, Kirchberg Tirol, Austria, International conferenceROOM-TEMOERATURE RAMAN and OPTICAL CARBON NANOTUBES.
Oral presentation
- 4th International Conference Porus Semiconductor Science and Technology., Mar. 2004, English, 未記入, Cullera-Valencia Spain., International conferencePhotosensitization of Oxygen Molecules by Exciton confined in Silicon Nanocrystals.(Extended abstact O-06 pp.29)
Oral presentation
- 4th International Conference Porus Semiconductor Science and Technology., Mar. 2004, English, 未記入, Cullera-Valencia, Spain, International conferenceOptical devices based on anistropically nanostructured silicon.(Extended abstruct O-30 pp.74-75)
Oral presentation
- 4th International Conference Porus Semiconductor Science and Technology., Mar. 2004, English, 未記入, Cullera-Valencia, Spain, International conferenceLight Amplification in a liquid network confined in a porous matrix.(Extended abstruct O-30 pp.120-121)
Oral presentation
- 第51回応用物理学会関係連合講演会 予稿集第3分冊 p.1593, Mar. 2004, Japanese, 応用物理学会, 東京, Domestic conferenceB,Pを同時ドープしたSiナノ結晶の発光特性（Ⅲ）
Oral presentation
- Nanotech 2004, 2004, Japanese, 未記入, Batz sur mer,France, International conferenceComplex Optical Characterization of Carbon Peapod
Oral presentation
- 2003 MRS fall meeting, Nov. 2003, English, 未記入, USA, International conferenceElectornic Energy Transfer from Photoexcited Silicon Nanocrystals to Molecular Oxygen.
Oral presentation
- The International Conference on Advanced Laser Technologies 11th Annual Meeting (ALT03)Focused on Biomedical Optics., Sep. 2003, English, 未記入, Bedfordshire,UK, International conferencePhotosensitization of Oxygen Molecules by Exciton confined in Silicon Nanocrystals.
Oral presentation
- 第64回応用物理学学術講演会 予稿集第3分冊 p.1297, Aug. 2003, Japanese, 応用物理学会, 福岡, Domestic conference複屈折特性を持つポーラスSiの偏光ラマン散乱
Oral presentation
- 第64回応用物理学学術講演会 予稿集第3分冊 p.1298, Aug. 2003, Japanese, 応用物理学会, 福岡, Domestic conferenceSiナノ結晶からのエネルギー移動による一重項酸素の生成
Oral presentation
- 第64回応用物理学学術講演会 予稿集第3分冊 p.1310, Aug. 2003, Japanese, 応用物理学会, 福岡, Domestic conferenceSiナノ結晶からEr3+へのエネルギー移動
Oral presentation
- European Materials Research Society Spring Meeting (E-MRS 2003), Jun. 2003, English, 未記入, Strasbourg France, International conferenceEvalution of the Energy Transfer Rate Between Erbium Ions and Silicon Nanocrystals in Silicon Dioxide.
Oral presentation
- European Materials Research Society Spring Meeting (E-MRS 2003), Jun. 2003, English, 未記入, Strasbourg, France, International conferenceEnergy Transfer from Silicon Nanocrystals to Erbium Ions- What is the Factor Determining the Energy Transfer Rate?
Oral presentation
- 2003 MRS Spring Meeting, Apr. 2003, English, 未記入, San Francisco, USA, International conferencePhotosensitization of Oxygen Molecules by Excitons Confined in Silicon Nanocrystals. (Abstract p.186)
Oral presentation
- 2003 MRS Spring Meeting, Apr. 2003, English, 未記入, San Francisco, USA, International conferenceOptical properties of Silicon Nanocrystal Assembly -Effect of Inpurity Atoms and Impurity Molecules.(Abstract p.186)
Oral presentation
- 第50回応用物理学関係連合講演会, 2003, Japanese, 応用物理学会, 神奈川大学, Domestic conferenceポーラスSiからのエネルギー移動による一重項酸素の生成
Others
- ナノ学会創立大会, 2003, Japanese, ナノ学会, 神戸, Domestic conferenceナノメートルサイズ領域でのSi結晶の新しい機能－光増感剤としてのSiナノ結晶－
Oral presentation
- 第64回応用物理学学術講演会 予稿集第3分冊 p.1296, 2003, Japanese, 応用物理学会, 福岡, Domestic conferenceB, Pを同時ドープしたSiナノ結晶の発光特性（Ⅱ）
Oral presentation
- 第50回応用物理学関係連合講演会, 2003, Japanese, 応用物理学会, 神奈川大学, Domestic conferenceB,Pを同時ドープしたSiナノ結晶の発光特性
Others
Association Memberships
Research Projects
- 日本学術振興会, 科学研究費助成事業 基盤研究(B), 基盤研究(B), 神戸大学, 01 Apr. 2021 - 31 Mar. 2025トロイダル双極子共鳴のデバイス応用に向けたメタサーフェスプラットホームの構築
- 日本学術振興会, 科学研究費助成事業 基盤研究(B), 基盤研究(B), 東京工業大学, 01 Apr. 2021 - 31 Mar. 2024アキラル構造からなる光角運動量ソーターの多空間同時光計測による研究
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Fund for the Promotion of Joint International Research (Fostering Joint International Research (B)), Fund for the Promotion of Joint International Research (Fostering Joint International Research (B)), Kobe University, 09 Oct. 2018 - 31 Mar. 2024Development of biophotonics and photochemical applications of silicon quantum dots in collaboration with a consortium established for the formation of "Silicon Nanomaterials Center" founded by US NSF
- 日本学術振興会, 科学研究費助成事業 挑戦的研究(萌芽), 挑戦的研究(萌芽), 神戸大学, 28 Jun. 2019 - 31 Mar. 2022シリコン量子ドット薄膜のキャリア精密制御とマトリックスエンジニアリング
シリコン量子ドットは，環境親和性・生体親和性の高い新ナノ材料であり，既存の半導体デバイス・プロセスと高い整合性を有している．本研究では，独自に開発したコア／シェル構造シリコン量子ドットの塗布薄膜の電気伝導特性を向上させ，それにより実用レベルの光・電子デバイスを実現するための基盤技術を確立することを目的とする．そのために，薄膜形成技術の開発，ドーピングによるキャリア制御，シリコン量子ドット間を金属イオンや金属ナノ粒子で架橋した複合薄膜の形成による電子移動度の向上等に関する研究を行う．本年度は、以下の研究を実施した。 i) コロイド状シリコン量子ドットを基板上に塗布する方法で、シリコン量子ドット光電極を作製した。水溶媒中において従来のシリコン量子ドットから作製した光電極では、量子ドットの自己酸化に起因するアノード電流が観測されたが、コア／シェル構造シリコン量子ドットでは、カソード電流（プロトンの還元電流）が観測された。カソード電流の大きさは量子ドットのサイズに依存することが明らかになった。 ii) シリコン量子ドット光電極の性能向上を目的に、助触媒としてプラチナナノ粒子を付加する方法の開発を行った。シリコン量子ドット分散溶液に塩化プラチナ酸を加えることにより量子ドット表面にプラチナナノ粒子を成長させる方法を試みた。その結果、複合ナノ粒子は形成されたが、光電極としての機能は消失した。そこで、シリコン量子ドット光電極表面にあらかじめ形成したプラチナナノ粒子の溶液を塗布する方法を検討し、この方法では光電極として機能することを確認した。 iii) 同様に、シリコン量子ドットとグラフェンもしくは酸化グラフェンのナノ粒子の複合構造の検討を行った。様々なプロセスと構造について検討を行い、現在のところグラフェンナノ粒子層とシリコン量子ドット層の積層構造で最も良好な光電極特性が得られている。
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Grant-in-Aid for Scientific Research (C), Kobe University, 01 Apr. 2019 - 31 Mar. 2022Photofunctional Near-Field Fano Resonances in Multilayer Systems and Their Applications
現在までの研究で、多層膜系で出現するFano共鳴の根源は、ブロードな共鳴を示す平面導波路内での局所電場がFano共鳴の挙動を示すことにあることが示唆されてきた。通常、導波路内の局所電場の振舞いは、電磁気理論計算によって推測されるのみで、直接実験で観測することはできない。昨年度は、この弱点を克服するため、導波路層に蛍光色素をドープし、導波路内の局所電場によって励起される色素からの発光スペクトルを観測することにより、局所電場を直接的にモニターできることを示した。今年度は、この技術をさらに発展させ実験を継続するとともに、局所電場の振舞いをさらに詳しく理論解析した。その結果、以下のような成果が得られた。 １．蛍光測定による局所電場の直接観察：多層膜系のFano共鳴は、ブロードな導波モードとシャープな導波モードの結合により達成される。２つの導波路に異なる発光波長を持つ蛍光色素をドープし、異なる波長で発光をモニターすることにより、２つの導波路の局所電場を別々に追跡することに成功した。この方法を用いて、モード間結合の強さを系統的に変化させ、Fano挙動の変化、さらには結合モードと局所場との関係性を明らかにすることができた。今回観測された、発光スペクトルの特異な形状は、種々のセンサーや、増強分光等に応用が可能である。 ２．導波路層内の電場解析：ブロードな共鳴を示す導波路層内の電場分布を詳細に検討した結果、導波路層内の位置によって異なるFano形状が実現されていることが判明した。さらに、異なるFano形状を層の全体に渡って積分した結果もFano形状になることが分かった。これは、ミクロとマクロ両方のスケールでFano形状が実現されていることを物語っている。
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), Kobe University, Apr. 2016 - Mar. 2020, Principal investigator
Silicon quantum dots are known to have high biocompatibility and biodegradability, and are expected as new nanofluorescent materials that replace conventional heavy metal-based quantum dots in the biophotonics field. The purpose of this study was to establish the fundamental technology that is essential for the application of silicon quantum dots to biophotonics. For water-dispersible silicon quantum dots developed by our group, optimization of the structure, reduction of the size distribution, development of surface modification technology, and development of the technology to bind antibody were performed. Furthermore, fluorescent bioimaging by using the silicon quantum dots was demonstrated and the cytotoxicity was examined. Development of a plasmonic substrate for the enhancement of the sensitivity of fluorescent biosensors was performed and a high performance plasmonic substrate was realized.
Competitive research funding
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Grant-in-Aid for Scientific Research (C), Kobe University, Apr. 2016 - Mar. 2019
Over the past ten years, Fano resonances in metallic and dielectric nanostructures and metamaterials have been extensively studied. However, the nanofabrication of the nanostructures and metamaterials requires high cost procedures and time consuming. Furthermore, it is not easy to achieve high Q resonances due to fabrication imperfections. To overcome these difficulties, we attempted to realize and control high Q Fano resonances using planar multilayer structures, which can be fabricated easily by low cost procedures in short time. We could realize the Fano resonance with a Q value as high as 2800, which is much higher than the values reported so far. Incorporating photofunctional dye molecules into the multilayer structures, we succeeded in controlling the Fano resonance by irradiation of external light.
Competitive research funding
- 国際科学技術共同研究推進事業（戦略的国際共同研究プログラム）（SICORP）, 2016, Principal investigator【SICORP】金属－IV族半導体ナノ複合体のナノフォトニクス：単一ナノ粒子から機能性集合体まで
Competitive research funding
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research, Grant-in-Aid for Challenging Exploratory Research, Kobe University, Apr. 2012 - Mar. 2015, Principal investigator
Colloidal silicon (Si) nanocrystals have been attracting significant attention as a precursor for a future printable electronics and in biomedical applications. In this project, we will develop Si nanocrystals that can be dispersed in polar solvents without organic capping. We have succeed in developing boron (B) and phosphorus (P) co-doped Si nanocrystals and found that the co-doped nanocrystals can be dispersed in polar solvents without any surface functionalization processes. From detailed structural analyses, we showed that the surface of co-doped nanocrystals are covered by high B and P concentration shells and the shells induce negative potential, which prevent agglomeration of nanocrystals by electrostatic repulsions. We succeeded in controllingl the size of nanocrystals from 1 to 14 nm, which resulted in very wide tunable range of the luminescence energy (0.85-1.85 eV). We also succeeded in producing high quality Si nanocrystal solids by spin-coating colloidal solutions.
Competitive research funding
- 日本学術振興会, 特別研究員奨励費, 特別研究員奨励費, 神戸大学, Apr. 2012 - Mar. 2015, Principal investigator
半導体ナノワイヤは，量子サイズ効果によりバルク半導体結晶には見られない興味深い物性を示す事から電子デバイス材料として注目されている。本研究では環境親和性が高い2種類の半導体材料，シリコン（Si)と酸化亜鉛（ZnO)，のナノワイヤの物性をさらに制御し，より有用な材料を創成することを目的に，ドーピングによる格子歪の導入，無機‐無機もしくは無機‐有機ヘテロ構造ナノワイヤの形成を行う。本年度は，以下の研究を実施した。 １）Siナノ結晶への歪の導入と三次非線形光学応答の増大。ボールミリングにより直径10－42nm程度のSiナノ結晶を作製し，X線回折とTEMにより歪を評価した。歪の導入がSiナノ結晶の3次非線形光学応答に及ぼす影響について研究を行ったところ，2光子吸収係数と非線形屈折率が歪量に依存して変化することが明らかになった。特に歪量0.2－0.5％の領域において2光子吸収係数が単調に減少し非線形屈折率が単調に増加することを見出した。本研究の結果は，歪の導入による特性制御がSiナノ構造の非線形光学素子応用において有効であることを示している。 ２）EuドーピングによるZnOナノワイヤの第二次高調波発生（SHG）増強。ZnOナノワイヤは高い第二次高調波発生（SHG）効率を有することが知られている。不純物のドーピングによる結晶格子歪の導入によりZnOナノワイヤのSHG効率をさらに増大することを試みた。その結果，ユーロピウム（Eu）ドーピングによりSHGが大きく増大することを見出した。SHG強度はEu濃度が約0.5 at.%の時に最大となった。有効SHG係数増大のメカニズムを解明するために，フォトルミネッセンススペクトルのシュタルク分裂よりZnO結晶の対称性崩れの大きさを見積もった。有効SHG係数とZnO結晶の対称性崩れの大きさの間に強い相関が見られることから，EuドーピングによるZnO結晶の格子の歪がSHG増大の原因であると考えらえる。
Competitive research funding
- 日本学術振興会, 二国間交流事業（チェコとの共同研究）, 2015, Principal investigator二国間交流「不純物ドープSiナノ結晶：フォトニクス，バイオ応用に向けた新奇ナノマテリアル開発」
Competitive research funding
- 科学技術振興機構, 国際科学技術共同研究推進事業（SICORP）, 2015, Principal investigator金属-IV族半導体ナノ複合体のナノフォトニクス：単一ナノ粒子から機能性集合体まで
Competitive research funding
- 二国間交流事業（チェコとの共同研究）, 2014, Principal investigator二国間交流「不純物ドープSiナノ結晶：フォトニクス，バイオ応用に向けた新奇ナノマテリアル開発」
Competitive research funding
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), Kobe University, 2011 - 31 Mar. 2015, Principal investigator
The purpose of this work is to realize new silicon (Si) nanocrystal-based functional materials by impurity doping in combination with the quantum size effects. In nanocrystals, confined excitons can interact with impurities on the surface. Therefore, chemical elements with very small solid solubility in bulk Si crystal can be doped to Si nanocrystals. We will develop Si nanocrystals in which different kinds of impurity atoms, e.g., n- and p-type shallow impurities, rare earth ions, bismuth ions, etc., are doped and reveal the linear and nonlinear optical properties.
Competitive research funding
- 研究成果最適展開支援プログラム フィージビリティスタディステージ 探索タイプ 一般型, 2011, Principal investigatorA-STEP「サブ波長構造紫外光用トゥルーゼロオーダー波長板の開発」
Competitive research funding
- 日本学術振興会, 科学研究費助成事業 特定領域研究, 特定領域研究, 神戸大学, 2009 - 2010非金属系ナノ構造による光電場増強機能の創出
金属ナノ構造を用いた蛍光増強の場合,励起分子が金属表面の極く近傍に位置するとき,エネルギー移動によって蛍光がクエンチするという難点があった.本研究は,そのような難点を克服し,蛍光増強の新しい場を提供するため,非金属ナノ構造によるクエンチなしの蛍光増強を実現することを目的としている. 本年度は,昨年度までに得られれたGaP微粒子層上のRohdamine B分子の蛍光増強の結果をさらに発展させ,特に蛍光増強のメカニズムを探る研究を実験,理論の両面から行った.微粒子層としては,GaP微粒子のみならず、新しい方法(パルスレーザーアブレーション法)で作製したSi微粒子についても実験を行った.色素層としては,従来のRohdamine Bの他ににDCMを用いた.また,単純な蛍光スペクトルの測定に加えて,蛍光励起スペクトル,微粒子層の減光スペクトル,散乱スペクトルの測定を行った.また,理論的には電場増強度Q_
の計算に,微粒子のサイズ分布を取り入れた. これらの測定と計算を通じて,以下のような結果が得られた.1)Rhodamine B分子と同様に,DCM分子でも,クエンチ無しでの蛍光増強が見られる.2)サイズの大きいGaP微粒子での蛍光増強では,蛍光励起スペクトルにピークが現れる.3)励起スペクトルのピークは,サイズ分布を取り入れたQ_ の計算結果と定性的に一致する.これらのことは,非金属微粒子層上の有機分子の蛍光増強は,電磁気学的なメカニズムで生じており,特に入射光側の共鳴が増強に効いていることを示唆している. - 科学研究費補助金／特定領域研究, 2010
Competitive research funding
- 日本学術振興会, 科学研究費補助金／特定領域研究, 特定領域研究, 神戸大学, 2008 - 2008
従来は、金属のナノ構造を用いて、表面プラズモン励起に伴う局所電場増強を使うことにより、表面増強ラマン散乱や蛍光増強が達成されていた。ところが、蛍光増強の場合、励起分子が金属表面の極く近傍に位置するとき、エネルギー移動によって蛍光が失活するという難点があった。本研究は、そのような難点を克服し、蛍光増強の新しい場を提供するため、非金属ナノ構造による失活なしの蛍光増強を実現することを目的としている。 本年度は、先ず非金属ナノ構造でも電場増強が可能か否かを明らかにするため、Mie散乱の理論から導かれる近接場増強度を、種々の物質の球形粒子について見積もった。その結果、半導体のGaP及びSiが高い増強度を示し、有力な候補物質であることが判明した。非金属微粒子には、表面プラズモン励起は存在しない。しかしこのような電場増強が得られるのは、微粒子の電磁気的な固有振動が励起されるためであり、今回の計算で予言された増強は、微粒子のTE_1,TM_1モードの励起によるものである。 実験では、ガス中蒸発法により、MgO、ZnO、MoO_3、WO_3、GaPの微粒子層を作製し、その上にDCM又はrhodamine Bの色素分子層を堆積し、蛍光測定を行った。いずれの微粒子層についても、増強度の大小はあるものの、蛍光増強が観測された。特に、GaP微粒子層上に種々の膜厚のrhodamine B層を堆積し増強度を測定したところ、膜厚の減少とともに増強度が増大し、最大で140倍の増強度が得られた。これは、非金属微粒子表面で、失活なしの蛍光増強が実際に生じることを示している。
Competitive research funding
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Grant-in-Aid for Scientific Research (C), Kobe University, 2008 - 2010
In order to realize organic light emitting devices without transparent ITO electrodes, experimental and theoretical studies were performed. Metal-Insulator-Metal (MIM) structures having an organic light emitting layer at the center of the structures were prepared and their emission properties were measured. An intensity enhancement of ~25 was observed in good agreement with theoretical estimates. The intensity enhancement can be well explained in terms of light emission mediated by symmetric surface plasmon polaritons in the MIM structure. Results of simulations for realistic light emitting devices indicate that the light-extraction efficiency is greatly enhanced when an ITO electrode is replaced by an Ag electrode. The present results suggest that organic light emitting devices with high efficiencies can be constructed without ITO electrodes.
Competitive research funding
- 日本学術振興会, 特別研究員奨励費, 特別研究員奨励費, 神戸大学, 2007 - 2009, Principal investigator
受人研究者がこれまで行ってきた、希土類イオンとシリコン(Si)ナノ結晶をドービングしたシリカガラス薄膜に関する研究を拡張し、様々な発光センターとSiナノ結晶を同時にドーピングした多成分ガラス薄膜の開発を行う。このような系ではSiナノ結晶の光増感作用により発光センターを高効率に励起できる可能性がある。研究の長期的な目標は、このような系を用いて既存の光増幅器に取って代わるコンパクトな光増幅器を実現することである。今年度は、発光センターとしてビスマス(Bi)イオンに注目した。Biは、固体中で様々な価数を取り、可視から近赤外領域に非常に広帯域の発光を示す。特に、近赤外領域の発光は、光ファイバー通信用光増幅器への応用から注目を集めている。まず、近赤外領域に高効率に発光するBiドープバルクガラスを作製した。このガラスをターゲットし、スパッタリングによりBiドープガラス薄膜を作製した。作製した薄膜は、近赤外領域に発光を示した。さらに、Biドープガラス薄膜とSiナノ結晶層を交互にスパッタ堆積することにより多層膜試料を形成した。この方法では、発光層と光増感剤(Siナノ結晶)層が別々に形成されるため、作成条件的自由度が高く、それぞれの層を個別に最適化できるというメリットがある。様々な条件で試料を作製し、光学特性の評価を行ったところ、多層膜は単層膜に比べて発光効率が大きく増大することが明らかになった。また、発光励起スペクトルから、Siナノ結晶からのエネルギー移動によるBiイオンの励起を確認することに成功した。以上の研究と並行して、ゼオライト粒子にBiイオンや希土類イオンをドーピングすることにより、高効率近赤外発光粒子を形成する研究を行った。その結果、非常に簡便な方法で、多様な発光センターをゼオライト粒子にドーピングすることに成功した。開発した粒子を出発物質とし、様々な近赤外光デバイスの実現が可能だと考えている。
Competitive research funding
- 日本学術振興会, 科学研究費補助金／特定領域研究, 特定領域研究, 神戸大学, 2007 - 2007, Principal investigator
量子サイズ効果が顕著にあらわれるサイズ領域の半導体に不純物をドーピングすると、その振る舞いはバルク結晶にドーピングしたものと大きく異なる。特に、ドナー、アクセプターのイオン化エネルギーの増大等の本質的な変化が顕著に現れる。本研究は、ボトムアップ方式により不純物をドーピングしたシリコンナノ結晶を作成し、シリコンナノ結晶中の不純物原子の電子状態について基礎的な情報を得ることを目的とする。本研究が対象とするサイズ領域では電気的な評価が非常に困難であるため、光(電磁波)を用いた研究が重要になる。本年度は不純物をドーピングしたシリコンナノ結晶の電子スピン共鳴(ESR)測定よりその電子状態について知見を得ることを目的に研究を行った。その結果,以下のことが明らかになった。(1)シリコンナノ結晶では、不純物濃度が非常に高い状況においても、ESRの温度依存性はCurie則に従う。これは、シリコンナノ結晶が縮退半導体にならないことを示唆している。(2)P,B同時ドーピングシリコンナノ結晶のESRの線幅は単独ドーピングの場合に比べて広い。特に、キャリアが補償されているであろう状況において最大となる。これは、n型とp型の不純物をドーピングしたシリコンナノ結晶においては、キャリアが強く局在することを示唆している。これには、不純物の静電場による局在と量子閉じ込め効果による局在の両方が関与していると考えられる。(3)この強い局在が、室温におけるD-Aペアの強い発光の起源であると考えられる。
Competitive research funding
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A), Grant-in-Aid for Scientific Research (A), Kobe University, 2004 - 2006Research on energy transfer via nanocrystals and their new functionality as optical materials
In this work, a new function of nanocrystals as "energy donor" or "energy transmitter" in an energy transfer process is studied. Followings are the list of results obtained in this work. 1. The mechanism of energy transfer from Si nanocrystals to Er ions is studied and the existence of two different energy transfer processes is revealed. 2. The evidence of the interaction between impurities (P and/or B atoms) in Si nanocrystals and Er ions is shown and efficient deexcitation of Er ions by Auger type energy transfer to impurities in Si nanocrystals is clarified. 3. The rate of energy transfer from Si nanocrystals to Er ions is shown to be modified by placing a metal thin film nearby. The results strongly suggest that the energy transfer efficiency can be enhanced by using a metal layer. 4. The enhancement of PL from Er in glasses by simultaneoulsy doping gold nanocrystals is demonstrated and the contribution of surface plasmon polaritons of Au nanocrystals for the enhancement is clarified. 5. Excitation of surface plasmon polaritons of a gold thin film by energy transfer from Si nanocrystals is demonstrated by placing a gold thin film and organic grating near Si nanocrystals.
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), Kobe University, 2006 - 2008, Principal investigator
「Siナノフォトニクス」と「プラズモニクス」を融合し、新しいナノ複合光学材料を実現することを目的に研究を行った。Si系発光材料に及ぼす金属表面や金属ナノ構造の影響について包括的な研究を行った結果、金属ナノ構造によりSi系発光材料の特性を大きく変化させることができるだけではなく、Siナノ結晶から希土類イオンへのエネルギー移動レートを制御できる可能性があることが明らかになった。また、表面プラズモン励起がアップコンバージョン発光増強に有効であることを示した。
Competitive research funding
- 2006, Principal investigatorSiナノ結晶をベースとする一重項酸素発生光増感剤の開発－発生メカニズムの解明及び、化学、生物、食品分野への応用の探求－
Competitive research funding
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Grant-in-Aid for Scientific Research (C), Kobe University, 2003 - 2005High efficient photoluminescence from isoelectric impurities in quantum confined Si nanocrystals
The purpose of this work is to form an isoelectric trap in Si nanocrystals by simultaneously doping n and p type impurities. We have developed a method to prepare P and B codoped Si nanocrystals, and studied the optical properties in detail as functions of P and B concentration. The photoluminescence intensity of carrier-compensated Si nanocrystals was larger than that of either n or p type impurity doped Si nanocrystals, and sometimes it was larger than that of pure Si nanocrystals. Furthermore, the tunable range of photoluminescence energy is extended to below the bandgap energy of bulk Si crystals. By properly controlling the impurity concentration and size of Si nanocrystals, the photoluminescence energy was controlled from 0.9eV to 1.5eV without losing the intensity so much. The carrier compensated Si nanocrystals also act as an efficient photo-sensitizer for rare-earth ions. It has been demonstrated that the carrier compensated Si nanocrystals can excite Er ions placed nearby quite efficiently. The photoluminescence intensity of Er ions in carrier-compensated Si nanocrystals was larger than that in pure Si nanocrystals. Although we could successfully demonstrate that the formation of isolectric centers in Si nanocrystals is possible and these nanocrystals exhibit characteristic features, which are absent in pure Si nanocrystals, the electronic structures of impurity doped Si nanocrystals are still not fully clarified. In order to extend the functionality of Si nanocrystals and explore the applications, deeper understanding of the electronic structures is indispensable, and will be a target of future research.
- 科学研究費補助金／基盤研究(C), 2005, Principal investigator
Competitive research funding
- 科学研究費補助金／基盤研究(A), 2005
Competitive research funding
- 2005, Principal investigatorSiナノ結晶をベースとする一重項酸素発生光増感剤の開発－発生メカニズムの解明及び、化学、生物、食品分野への応用の探求－
Competitive research funding
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), Kobe University, 2001 - 2003Development of Efficient Si-nanocrystal-sensitized optical waveguide amplifiers
Er doped SiO_2 films containing Si nanocrystals as sensitizers have been investigated for an application to an efficient optical-amplifier. We demonstrate an optical-amplifier gain of 991cm^<-1> measured by the VSL (variable strip length) method at a wavelength of 1.55 μm using a slab waveguide. The amplification in the VSL measurement is observed within irradiation length of 60 μm in the slab waveguide. It has been found that the silicon-nanocrystals size (that is controlled by the annealing temperature) is very important to decrease the waveguide loss caused by excitons generated in the silicon nanocrystals. Core films containing silicon nanocrystals whose diameter is less than 2.7 nm show positive gain (that is amplification), because the above mentioned waveguide-loss is low. Sputtering and microfabrication processes to develop the optical amplifiers are deposition and RIE (reactive ion etching) of core patterns. A uniform core-film (4cmx8cm area) has been achieved on a 4 inch silicon wafer with a uniformity of ± 10 % in the photoluminescence intensity and the film thickness. 6 μm deep patterns in silica films have been fabricated using RIE, which can be used to fabricate the optical amplifiers. If the practical planar waveguide amplifier is realized at the wavelength of 1.55 μm used in optical telecommunication networks, a variety of novel photonic devices can be developed, because a new functionality is added to passive silica-based waveguide components.
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B), Grant-in-Aid for Scientific Research (B), Kobe University, 1999 - 2001Structure and Electronic States of Carbon Onions
In this research project, we have performed a systematic study on the structure, and electronic states of carbon onions and carbon nanocapsules. Major results obtained are summarized as : 1) Structure and electronic states of carbon onions : By annealing the nanodiamond particles 5nm in size in high vacuum, we could mass produce while spherical onions at around 1700℃ and polyhedral onions above 2100℃. Combining the results of high-resolution TEM, EELS, ESR, Raman spectroscopy and X-ray diffraction, we could conclude that the spherical onions have defective structures rather than the perfect fullerene structure. They possess dangling bonds and localized electronic states. On the other hand, the polyhedral onions are more graphitic and contain de-localized πelectrons. 2) Thin films of carbon nanocapsules containing magnetic metallic particles : By means of co-sputtering and post-annealing, we could prepare thin films of carbon nanocapsules containing Ni, and NiCo alloy nanocrystals. By adjusting the alloy composition, the optimum magnetic characteristics could be achieved. 3) Carbon onions as a candidate of interstellar dust : We measured the UV-Visible extinction spectra for carbon onions prepared from nanodiamonds and dispersed in pure water. Measured spectra could successfully be reproduced by theoretical calculations, which assume the aggregation of defective onions dispersed in water. Extending the calculation to an isolated spherical onion placed in vacuum, we could obtain an extinction spectrum that agrees very well with a measured interstellar extinction spectrum. This good agreement strongly suggests that the defective onions are one of the components of the interstellar dust.
- 日本学術振興会, 科学研究費助成事業 奨励研究(A), 奨励研究(A), 神戸大学, 1999 - 2000Siナノ結晶へのn、p型不純物同時ドーピングによるナノpn接合の形成
本研究は、直径数ナノメートル程度のSiナノ結晶に、PやBをドーピングしナノメートルスケールのpn接合を形成することを最終目的としている。前年度までは、Pを低濃度にドープすると欠陥が解消し発光効率が改善すること、及び、ある濃度以上にドープすると、ナノ結晶内部で、Pドーピングにより供給された電子と光励起された電子-正孔対の間でAuger相互作用が可能になり、発光効率が急激に低下することを見出した。本年度は主にSi_<1-x>Ge_x混晶ナノ結晶に対して、不純物ドーピングの影響について研究を行なった。フォトルミネッセンス及び電子スピン共鳴(ESR)測定より、Si_<1-x>Ge_x混晶ナノ結晶の発光効率がSiナノ結晶に比べて非常に低いこと、及びSi_<1-x>Ge_x混晶ナノ結晶の表面には、Geダングリングボンド(Ge Pbセンター)が多数存在し、このダングリングボンドが発光効率低下の原因であることが明らかになった。Si_<1-x>Ge_x混晶ナノ結晶にPをドープすると、欠陥が劇的に解消され、発光効率が10倍以上改善することを見出した。これは、Pにより供給された電子がダングリングボンドを不活性化するためであると考えられる。さらにESR測定より、Pドーピングにより供給された電子は、Ge Pbセンターを優先的に不活性化した後、Si Pbセンター(Si、SiO2界面の酸素欠損欠陥)を不活性化することを明らかにした。可視-赤外光吸収測定を行なったところ、Pを高濃度にドープした試料で、赤外領域に単調に増加する吸収を見出した。この吸収は、伝導帯内の電子の遷移によるものであることから、すべての欠陥が解消すると、Pドーピングにより供給された電子は、自由電子としてふるまうことが明らかになった。本研究により、ナノメートルサイズのSi_<1-x>Ge_x混晶に不純物ドーピングによりキャリア制御が可能であることがはじめて明らかになった。
- 日本学術振興会, 科学研究費助成事業 特定領域研究(A), 特定領域研究(A), 神戸大学, 1999 - 1999ナノ粒子による近接場の局在と増強に関する研究
今年度は、微粒子(フォトニックドット)に局在するフォトンモードを介した共鳴トンネリング現象の解明を試みた。さらに、粗い金属表面上の表面プラズモンに付随する近接場を、ファイバープローブにより直接観測し、近接場の局在状態と表面粗さの関係について調べた。 1.フォトニックドットを介した共鳴フォトントンネリング フォトニックドットとしては誘電体微小球(Polystylene Sphere)を使用した。プリズムから全反射の条件で光を入射し、プリズム底面からEvanescent波を発生し、光のトンネルプロセスをi)Evanescent場によるWhispering Gallery Modes(WGM)の励起、及びii)WGMに付随する近接場のプリズムによるデカップリング、に分けて実験した。いずれの段階においても、WGM励起に対応する共鳴ピークが明確に観測された。 2.粗い金属表面上での表面プラズモン励起 種々の粗さを持つ銀表面を作製し、ATR法により表面プラズモンを励起した。さらに、表面プラズモン励起の条件化で、先端を尖鋭化した光ファイバーでEvanescent波の減衰距離を測定した。その結果、粗い表面上では、プラズモン励起の入射角度を変化させても、減衰距離がほぼ一定になることが見いだされた。
- 日本学術振興会, 科学研究費助成事業 奨励研究(A), 奨励研究(A), 神戸大学, 1998 - 1998不純物をドープした半導体ナノ結晶の作製と光学的特性の解明に関する研究
本研究では、Si、GeのIV族半導体ナノ結晶への不純物ドーピング技術の確立及びその評価技術の確立を目的としています。また、ナノ結晶中の不純物のドーピングに由来する物性変化を明らかにすることを目的としています。前年度は、不純物としてBをドープしたSiナノ結晶の発光を詳細に調べ、BをドーピングするとAuger過程による非発光再結合の割合が増加し、発光効率が低下することを示しました。本年度は主に、Siナノ結晶中にn型の不純物であるPをドーピングすることを試みました。その結果、Pをドーピングすると、Siナノ結晶のバンド端発光の効率が改善されることが明らかになりました。発光スペクトルの温度依存性を詳細に調べた結果、Pをドーピングすることにより、Siナノ結晶表面(Siナノ結晶とSiO_2マトリックスの界面)のダングリングバンドに起因する発光の強度が非常に弱くなることから、ダングリングボンドが減少していることが明らかになりました。さらに、発光減衰特性の測定から、ダングリングボンドの減少がバンド端発光効率の改善の原因であることを明らかにしました。過去に発表されているSiナノ結晶の発光効率を改善する方法は、ほとんどがSiナノ結晶表面を水素で終端するものであり、Pドーピングによる発光効率の改善の報告例はありません。以上の結果は、Siナノ結晶の発光効率を改善するための全く新しい方法を提供するものであり、非常に重要な成果であると考えています。
- 日本学術振興会, 科学研究費助成事業 特定領域研究(A), 特定領域研究(A), 神戸大学, 1998 - 1998SiO_2薄膜に埋め込まれた金属・半導体ナノ結晶の電気伝導特性に関する研究
本研究は、ナノメーターサイズの粒子を用い、室温付近の高温でクーロンブロッケードやクーロンステアケースといった単電子トンネリング現象を示す構造を作製することを目的としています。これまでに、同時スパッタリング法により、Au,Ag,Ge,Si等のナノメーターサイズの結晶を埋め込んだSiO_2薄膜を作成し、その断面方向の電流-電圧特性について研究を行ってきました。本年度は、以下の2つのテーマについて研究を行いました。(1)ナノ結晶のサイズを小さくすることにより、単電子トンネリング現象の発現する温度を高くする。(2)Siナノ結晶へ不純物(P)のドーピングを行い、単電子トンネリング現象への影響を調べる。(1)のテーマに関しては、Siナノ結晶のサイズを2nm程度まで小さくすることにより、室温付近でもクーロンステアケースを示す試料を作成することに成功しました。(2)のテーマに関しては、Pをドーピングすることにより、ドーピングしていない場合に比べて非常に単純で明瞭なクーロンステアケースが現れることを明らかにしました。この原因として、Pドーピングにより、ナノ結晶中に十分な数の自由電子が供給されたこと(Pドーピングを行っていない場合は、ナノ結晶中の自由電子の数はほとんど0であると考えられる)及び、ナノ結晶とSiO_2マトリックスの界面の欠陥が減少すること(発光測定より界面のダングリングボンドの減少を確認)を考えています。
- 日本学術振興会, 科学研究費助成事業 特定領域研究(A), 特定領域研究(A), 神戸大学, 1998 - 1998ナノ粒子による近接場の局在と増強に関する研究
本年度は、エヴァネッセント波の励起法の一つとして長距離伝搬表面プラズモン励起に着目し、非対称な媒質の効果を詳細に調べた。実験に用いた系は、//SF10プリズム/SiO_2ギャップ層/Ag又はAu薄膜/誘電率可変媒質//から成り、632.8nmHe-Neレーザー光を励起光源としATR測定を行った。誘電率可変媒質としては、種々の液体を使用した。可変媒質の誘電率が大きくなるに従って、i)長距離表面プラズモンの伝搬長が増す、ii)金属/媒質界面の電場増強度が上がる、iii)媒質内への電場の侵入長が長くなる、という結果を得た。さらに、昨年度観測されたフォトンの共鳴トンネリングが本当に電子の共鳴トンネリングと同等な現象であるかどうかを明らかにするために、電子の場合にもフォトンの場合にも有効な2×2Transfer Matrix法を用いて理論的考察を行った。その結果、観測されたフォトンの共鳴トンネル現象が電子の共鳴トンネル現象と同等とみなせることが結論された。
- 日本学術振興会, 科学研究費助成事業 重点領域研究, 重点領域研究, 神戸大学, 1997 - 1997ナノ粒子による近接場の局在と増強に関する研究
今年度は以下のような成果を得た。 1.ギャップモードの直接観測:今回、分光測定により微粒子と二次元表面の間に生じるギャップモードの振る舞いを直接的にとらえることを試みた。Al表面上にSpacer LayerとしてSiO_2膜をスッパタリングで着け、その上にAg Island粒子を蒸着で配置した。Spacer Layerの膜厚を種々変化させながら、試料の反射吸収スペクトルを測定した結果、Ag Island粒子による表面プラズモン吸収が観測され、粒子がAl表面から遠ざかるにつれ吸収ピークが長波長シフトすることが見いだされた。これは、ギャップモードに関する理論的予測と一致しており、ギャップモードの存在を直接的に示していると言える。 2.長距離伝搬モードの励起とラマン散乱の増強の観測:ATR法によって銅フタロシアニン膜に長距離伝搬モードを励起し、ラマン散乱の増強の測定を試みた。ATRスペクトルの鋭い落ち込みと同時にラマン強度が約百倍程度増強されていることが観測された。 3."共鳴"フォトントンネリングの観測:フォトンについても、電子と同様な"共鳴"トンネリング現象が存在することを実証した。Al薄膜をSiO_2のスッパタリング膜でサンドイッチした対称な系に、カップリング用及びデカップリング用のプリズムを配置した。ATRスペクトルの鋭い落ち込みに対応した入射角でトンネル光強度の鋭いピークが見られる。この現象は、Al薄膜の長距離伝搬表面プラズモンを介した。フォトンの共鳴トンネリングであると解釈できる。
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C), Grant-in-Aid for Scientific Research (C), Kobe University, 1996 - 1997"Impurity Doping into Semiconductor Nanocrystals"
The aims of this research project are, i) to establish the method of doping impurity atoms into semiconductor nanocrystals, ii) develop the analytical tools for verifying the doping and estimate the degree of doping, and iii) investigate the change in physical properties pf nanocrystals caused by doping, in particular, the optical properties. We could successfully dope B and P atoms into Si nanocrystals by applying the cosputtering technique. The success in doping could be verified by the appearance of Fano-type interference in Raman spectra. We could also successfully observe the change in the photoluminescence spectra caused by doping. The change in the photoluminescence spectra is believed to arise from the creation of excitons bound to the impurity states. Er and Yb ions could also be doped into SiO2 thin films containing Si nanocrystals. In the presence of Si nanocrystals, Er and Yb exhibited strong light emission, while the light emission was very weak, in the absence of Si nanocrystals. The strong light emission is caused by the energy transfer from Si nanocrystals to Er and Yb ions. The present results suggest the possibility of Si-based light emitting devices.
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