Directory of Researchers
| Hattori Yoshiaki |  |
| Graduate School of Engineering / Department of Electrical and Electronic Engineering | |
| Assistant Professor | |
| Electro-Communication Engineering |
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
Research Activities
Research Areas
Awards
Dec. 2019 第16回薄膜材料デバイス研究会, スチューデントアワード, フルオロベンゼンチオールを電極表⾯に修飾した有機薄膜トランジスタ
Nov. 2018 第15回薄膜材料デバイス研究会, スチューデントアワード, フルオロベンゼンチオール修飾による金表面の制御と有機トランジスタ応用
Japan society
Mar. 2016 日本応用物理学会, 学術講演会講演奨励賞
Published Papers
Abstract Exfoliated flakes of layered materials, such as hexagonal boron nitride (hBN) and graphite with a thickness of several tens of nanometers, are used to construct van der Waals heterostructures. A flake with a desirable thickness, size, and shape is often selected from many exfoliated flakes placed randomly on a substrate using an optical microscope. This study examined the visualization of thick hBN and graphite flakes on SiO2/Si substrates through calculations and experiments. In particular, the study analyzed areas with different atomic layer thicknesses in a flake. For visualization, the SiO2 thickness was optimized based on the calculation. As an experimental result, the area with different thicknesses in a hBN flake showed different brightness in the image obtained using an optical microscope with a narrow band-pass filter. The maximum contrast was 12% with respect to the difference of monolayer thickness. In addition, hBN and graphite flakes were observed by differential interference contrast (DIC) microscopy. In the observation, the area with different thicknesses exhibited different brightnesses and colors. Adjusting the DIC bias had a similar effect to selecting a wavelength using a narrow band-pass filter.
IOP Publishing, 09 May 2023, Nanotechnology, 34 (29), 295701 - 295701[Refereed]
Scientific journal
- Elsevier BV, Jan. 2023, Thin Solid Films, 764, 139631 - 139631
[Refereed]
Scientific journal
Abstract We propose a visualization technique for identifying an exfoliated monolayer hexagonal boron nitride (hBN) flake placed on a SiNx/Si substrate. The use of a Si substrate with a 63 nm thick SiNx film enhanced the contrast of monolayer hBN at wavelengths of 480 and 530 nm by up to 12% and −12%, respectively. The maximum contrast for the Si substrate with SiNx is more than four times as large as that for a Si substrate with a ∼90 or ∼300 nm SiO2 film. Based on the results of the reflectance spectrum measurement and numerical calculations, the enhancement is discussed.
IOP Publishing, 01 Aug. 2022, Applied Physics Express, 15 (8), 086502 - 086502[Refereed]
Scientific journal
A trimethylsilyl-monolayer modified by vacuum ultraviolet (VUV) light has been investigated for use in solution-processed organic thin-film transistors (OTFTs). The VUV irradiation changed a hydrophobic trimethylsilyl-monolayer formed from hexamethyldisilazane vapor into a hydrophilic surface suitable for solution processing. The treated surface was examined via water contact angle measurement and X-ray photoelectron spectroscopy. An appropriate irradiation of VUV light enabled the formation of a dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT) film on a modified monolayer by spin-coating. Consequently, the C8-BTBT-based OTFT with a monolayer modified for an optimal VUV irradiation time exhibited a field-effect mobility up to 4.76 cm2 V−1 s−1. The partial monolayer modification with VUV can be adapted to a variety of solution-processes and organic semiconductors for prospective printed electronics.
Corresponding, IOP Publishing, 01 Jun. 2022, Japanese Journal of Applied Physics, 61 (SE), SE1012 - SE1012[Refereed]
Scientific journal
Abstract Hexagonal boron nitride (h-BN) is an important insulating layered material for two-dimensional heterostructure devices. Among many applications, few-layer h-BN films have been employed as superior tunneling barrier films. However, it is difficult to construct a heterostructure with ultra-thin h-BN owing to the poor visibility of flakes on substrates, especially on a metallic surface substrate. Since reflectance from a metallic surface is generally high, a h-BN film on a metallic surface does not largely influence reflection spectra. In the present study, a thin Au layer with a thickness of ∼10 nm deposited on a Si substrate with a thermally grown SiO2 was used for visualizing h-BN flakes. The thin Au layer possesses conductivity and transparency. Thus, the Au/SiO2/Si structure serves as an electrode and contributes to the visualization of an ultra-thin film according to optical interference. As a demonstration, the wavelength-dependent contrast of exfoliated few-layer h-BN flakes on the substrate was investigated under a quasi-monochromatic light using an optical microscope. A monolayer h-BN film was recognized in the image taken by a standard digital camera using a narrow band-pass filter of 490 nm, providing maximum contrast. Since the contrast increases linearly with the number of layers, the appropriate number of layers is identified from the contrast. Furthermore, the insulating property of a h-BN flake is examined using a conductive atomic force microscope to confirm whether the thin Au layer serves as an electrode. The tunneling current through the h-BN flake is consistent with the number of layers estimated from the contrast.IOP Publishing, 05 Feb. 2022, Nanotechnology, 33 (6), 065702 - 065702[Refereed]
Scientific journal
- American Chemical Society (ACS), 15 Jul. 2021, The Journal of Physical Chemistry C, 125 (27), 14991 - 14999
[Refereed]
Scientific journal
An organic semiconductor film made of diphenyl derivative dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DPh-DNTT) has high carrier mobility. However, this mobility may be greatly affected by the crystal orientation of the DPh-DNTT's first layer. Polarization Raman microscopy is widely used to quantitatively analyze the molecular orientation, and thus holds great potential as a powerful tool to investigate the crystal orientation of monolayer DPh-DNTT with high spatial resolution. In this study, we demonstrate polarization Raman imaging of monolayer DPh-DNTT islands for crystal orientation analysis. We found that the DPh-DNTT sample indicated a strong dependence of the Raman intensity on the incident polarization direction. Based on the polarization dependence, we developed an analytical method of determining the crystal orientation of the monolayer DPh-DNTT islands and experimentally confirmed that our technique was highly effective at imaging the islands' crystal orientation with a spatial resolution of a few hundred nanometers.
Corresponding, 13 Apr. 2021, ACS omega, 6 (14), 9520 - 9527, English, International magazine[Refereed]
Scientific journal
Pentacene metal-oxide-semiconductor (MOS) capacitors with a SiO(2)dielectric treated by oxygen plasma have been studied by capacitance-voltage (C-V) measurements to investigate the energy distribution of the interface states. Oxygen plasma treatment, which is used for control of the threshold voltage in pentacene thin-film transistors, shifted theC-Vcurves of pentacene MOS capacitors to a positive gate voltage as well as the transfer curves of pentacene thin-film transistors (TFTs). The shift is explained by electrons captured at interface states generated by oxygen plasma treatment. The interface states capturing the electrons are expected to locate at low energy levels. The energy distribution of the interface states locating at middle or high energy levels was extracted by a method equivalent to the Terman method. By use of the method in two steps, the interface state densities distributed at middle and high energy levels (D(M)andD(H)) were separately obtained.D(M)andD(H)were of the order of 10(10)-10(12)cm(-2)eV(-1), and increased with an increase in plasma treatment time.
IOP PUBLISHING LTD, Dec. 2020, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 53 (50), English[Refereed]
Scientific journal
The initial stage of organic semiconductor film formation greatly affects the properties of films, which are used in organic devices including thin-film transistors and light-emitting diodes. Organic monolayer islands that are formed on a suitable substrate can be observed with a conventional optical microscope. Furthermore, the use of a polarized microscope allows the determination of the refractive index and crystal orientation of islands. Here, we report organic monolayer islands of 2,9-diphenyl-dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DPh-DNTT) deposited on a Si substrate with thermally grown SiO2 to investigate the crystal orientation of islands by polarized light microscopy. The observation of DPh-DNTT islands under polarized quasi-monochromatic light reveals that reflection intensity depends on both the crystal orientation and irradiation wavelength. A comparison between experimental and calculated reflection intensities provides an estimate of an anisotropic complex refractive index in the plane. The crossed-polarized microscopy image of a SiO2/Si substrate with DPh-DNTT islands shows that the contrast between the islands and SiO2 surface is sensitive to the angle between the polarizer and analyzer and depends on the direction of crystal orientation. The dependence of reflection contrast, which can be explained by the anisotropic extinction coefficient, is used to confirm crystal orientation.
American Chemical Society (ACS), 12 Aug. 2020, ACS applied materials & interfaces, 12 (32), 36428 - 36436, English, International magazine[Refereed]
Scientific journal
The capacitance characteristics of pentacene metal-oxide-semiconductor (MOS) capacitors with a large uncovered pentacene area have been investigated. The capacitance measured was examined by assuming that the uncovered area is represented by a distributed constant circuit. The frequency dependence of the capacitance was reproduced by an equation derived based on the assumption. The sheet resistance for the uncovered area of a MOS capacitor was calculated as a function of the gate voltage from the capacitance measured. The mobility of a MOS capacitor with an uncovered area was estimated by fitting a curve to the gate voltage dependence of the sheet resistance, and was in the range of 0.48-0.64 cm(2) V-1 s(-1). In addition, the mobilities were compared with those calculated from the current-voltage characteristics of pentacene transistors fabricated on the same substrate. (c) 2020 The Japan Society of Applied Physics
IOP PUBLISHING LTD, Mar. 2020, JAPANESE JOURNAL OF APPLIED PHYSICS, 59 (3), 036503 - 036503, English[Refereed]
Scientific journal
Mixed monolayers consisting of 4-fluorobenzenethiolate and 1-octadecanethiolate on Au surfaces were formed by immersing in an ethanol solution of 4-fluorobenzenethiol (FBT), and subsequently by immersing in that of 1-octadecanethiol (ODT). To obtain systematically a mixed monolayer, the formation of FBT- and ODT-monolayers was investigated with respect to the reaction time and concentration of the solution. The monolayer formed on a Au surface was evaluated based on the work function, the water contact angle, and the X-ray photoelectron spectroscopy (XPS) spectra measured. The XPS measurement of substrates prepared for formation of a mixed monolayer exhibited F 1s and C 1s spectra supporting the presence of a mixed monolayer consisting of 4-fluorobenezenethiolate and 1-octadecanethiolate. (C) 2019 The Japan Society of Applied Physics
IOP PUBLISHING LTD, Mar. 2020, JAPANESE JOURNAL OF APPLIED PHYSICS, 59 (SD), SDDA09 - SDDA09, English[Refereed]
Scientific journal
The formation and stability of a benzenedithiol monolayer on a Si substrate with a Au layer have been investigated to obtain a monolayer having high thermal stability as compared to that formed by use of a benzenethiol derivative. The monolayer was formed by immersing into an ethanol solution of 1,2-benzenedithiol (BDT). The work function of BDT-monolayer surface was measured for the investigation. The association constant for the adsorption of the molecules was estimated from the change of the work function. The subsequent annealing of the substrate with a BDT-monolayer at 500 K or lower did not lead to the change of the work function. Substrates with a BDT-monolayer were also examined using X-ray photoelectron spectroscopy (XPS). The work function and XPS spectra measured indicated that a BDT-monolayer formed on a Au surface is stable to annealing at temperatures up to about 473 K. (C) 2019 The Japan Society of Applied Physics
IOP PUBLISHING LTD, Mar. 2020, JAPANESE JOURNAL OF APPLIED PHYSICS, 59 (SD), SDDA03 - SDDA03, English[Refereed]
Scientific journal
Surface properties of Au electrodes modified by benzenethiol derivatives with a fluorine atom(s) have been methodically researched based on measurements of the work function and the contact angles. Benzenethiol derivatives with a fluorine atom(s) at ortho, meta, and/or para position were used for modification in this work. The measured work function was in a relatively wide range between 4.24-6.02 eV. The work function change from a bare Au surface was explained on the principle of dipole moments obtained by quantum chemical calculation. The water contact angle was found to vary between 64.8 degrees and 97.7 degrees. Furthermore, the surface tension was calculated from the measured contact angles of water and ethylene glycol. The calculated surface tension was reviewed from the perspective of the position of the substitute in the benzenethiol derivative. In addition, organic thin-film transistors (TFTs) with drain and source electrodes modified with 2-fluorobenzenethiol (2-FBT), 3-fluorobenzenethiol (3-FBT) or pentafluorobenzenethiol (PFBT) were characterized as other evaluations of the modified Au surface. The contact resistance in the TFT increased in the order of PFBT, 3-FBT and 2-FBT. The increase of the contact resistance was consistent with the decrease in the work function.
IOP PUBLISHING LTD, Mar. 2020, FLEXIBLE AND PRINTED ELECTRONICS, 5 (1), English[Refereed]
Scientific journal
Submonolayer two-dimensional (2D) islands of diphenyl dinaphthothienothiophene with various shapes and densities (N) were formed on a SiO2/Si substrate by controlling substrate temperature and the surface treatment for SiO2 in vacuum deposition to investigate the growth mechanism on the basis of their morphology. The statistical analysis shows that the 2D islands have complex shapes when N is small, and there is a constant relationship between N and the shape complexity of the 2D islands, regardless of the deposition conditions. Because the surface morphology is determined by diffusion coefficients for admolecules on a substrate surface (D-s) and along the edge of a 2D island (D-edg), the relationship between (N, shape complexity) and (D-s, D-edg) is studied. The statistical analysis indicates that D-edg is almost independent of the surface conditions and is instead determined by interactions with molecules constructing the 2D island. Therefore, D-edg is considered as a material-dependent parameter to control the morphology for growing high-quality films in vacuum deposition.
AMER CHEMICAL SOC, Jan. 2020, JOURNAL OF PHYSICAL CHEMISTRY C, 124 (1), 1064 - 1069, English[Refereed]
Scientific journal
The growth mechanism of 2,9-diphenyl-dinaphtho [2,3-b:2',3'-f]thieno [3,2-b]thiophene (DPh-DNTT) thin-films prepared by vacuum deposition was investigated based on the morphological crystallinity of the obtained films. In addition to atomic force microscopy, which is commonly used for imaging surface morphology, optical microscopy was also positively used for the same purpose. The technique allows the quick and easy evaluation of thin films. The optical microscopy images show that DPh-DNTT films grew according to a layer-by-layer growth mode. Each layer grew as flat two-dimensional (2D) islands with a thickness of about 2.3 nm, where DPh-DNTT molecules stand almost vertically on the substrate. The height difference between layers provided a color contrast in these images, which visualizes the initial 2D island on the Si substrate with thermally grown SiO2 and fractal-shape 2D islands on top surface. By using the method, a monolayer of isolated and round 2D islands, with a diameter of approximately 4 mu m, formed at a high substrate temperature on a SiO2 surface that had been previously treated with O-2 plasma or UV-O-3. The presence of a DPh-DNTT layer on the substrate was also confirmed by micro-Raman measurement.
ELSEVIER, Nov. 2019, ORGANIC ELECTRONICS, 74, 245 - 250, English[Refereed]
Scientific journal
The thin-films of 2,9-diphenyl-dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DPh-DNTT) prepared by vacuum deposition was observed by the optical microsope. By applying the dark-field mode in observation and/or image processing after imaging appropriately, morphological structure with a resolution of a few nanometers height was visualized easily and quickly. The technique can be used in a similar to atomic force microscopy, which is commonly used for imaging surface morphology. Moreover, the vibrational modes of a DPh-DNTT molecule calculated by quantum chemistry program is described as well as the comparison of the experimental Raman spectra for identification. The presented data are produced as part of the main work entitled "The Growth Mechanism and Characterization of Few-layer Diphenyl Dinaphthothienothiophene Films Prepared by Vacuum Deposition" (Hattori et al., 2019). (C) 2019 The Author(s). Published by Elsevier Inc.
ELSEVIER, Oct. 2019, DATA IN BRIEF, 26, 104522 - 104522, English, International magazine[Refereed]
Scientific journal
Pentacene thin-film transistors (TFTs) with controlled threshold voltages have been applied to a ring oscillator consisting of enhancement/depletion inverters for evaluation of the dynamic characteristics. The threshold voltage control was demonstrated by using oxygen plasma treatment to the SiO2 gate dielectric prepared by rf sputtering. The surface roughness of the SiO2 gate dielectric depended on the sputtering condition. The use of flat SiO2 gate dielectrics contributed to the improvement of the field-effect mobilities in pentacene TFTs. As a result, the ring oscillator operated at supply voltages of 15-25 V. The oscillation frequency was consistent with the result of circuit simulation for the ring oscillator. (C) 2019 The Japan Society of Applied Physics
IOP PUBLISHING LTD, Apr. 2019, JAPANESE JOURNAL OF APPLIED PHYSICS, 58 (SB), SBBJ04, English[Refereed]
Scientific journal
Hexagonal boron nitride (h-BN) is an important insulating substrate for two-dimensional (2D) heterostructure devices and possesses high dielectric strength comparable to SiO2. Here, we report two clear differences in their physical properties. The first one is the occurrence of Fermi level pinning at the metal/h-BN interface, unlike that at the metal/SiO2 interface. The second one is that the carrier of Fowler-Nordheim (F-N) tunneling through h-BN is a hole, which is opposite to an electron in the case of SiO2. These unique characteristics are verified by I-V measurements in the graphene/h-BN/metal heterostructure device with the aid of a numerical simulation, where the barrier height of graphene can be modulated by a back gate voltage owing to its low density of states. Furthermore, from a systematic investigation using a variety of metals, it is confirmed that the hole F-N tunneling current is a general characteristic because the Fermi levels of metals are pinned in the small energy range around similar to 3.5 eV from the top of the conduction band of h-BN, with a pinning factor of 0.30. The accurate energy band alignment at the h-BN/metal interface provides practical knowledge for 2D heterostructure devices.
AMER CHEMICAL SOC, Apr. 2018, ACS APPLIED MATERIALS & INTERFACES, 10 (14), 11732 - 11738, English, International magazine[Refereed]
Scientific journal
The electrical evaluation of the crystallinity of hexagonal boron nitride (h-BN) is still limited to the measurement of dielectric breakdown strength, in spite of its importance as the substrate for two-dimensional van der Waals heterostructure devices. In this study, physical phenomena for degradation and failure in exfoliated single-crystal h-BN films were investigated using the constant-voltage stress test. At low electrical fields, the current gradually reduced and saturated with time, while the current increased at electrical fields higher than similar to 8MV/cm and finally resulted in the catastrophic dielectric breakdown. These transient behaviors may be due to carrier trapping to the defect sites in h-BN because trapped carriers lower or enhance the electrical fields in h-BN depending on their polarities. The key finding is the current enhancement with time at the high electrical field, suggesting the accumulation of electrons generated by the impact ionization process. Therefore, a theoretical model including the electron generation rate by an impact ionization process was developed. The experimental data support the expected degradation mechanism of h-BN. Moreover, the impact ionization coefficient was successfully extracted, which is comparable to that of SiO2, even though the fundamental band gap for h-BN is smaller than that for SiO2. Therefore, the dominant impact ionization in h-BN could be band-to-band excitation, not defect-assisted impact ionization.
AMER PHYSICAL SOC, Jan. 2018, PHYSICAL REVIEW B, 97 (4), 045425, English[Refereed]
Scientific journal
We report the complete set of dielectric breakdown strength (EBD) for h-BN, that is, 12 MV/cm for out-of-plane EBD is four times higher than that for in-plane EBD and it is larger than that for diamond. The large anisotropy in dielectric constant (i.e., related with band gap) due to the layered structure causes this anisotropy.
Electrochemical Society Inc., 2017, ECS Transactions, 79 (1), 91 - 97, English[Refereed]
International conference proceedings
Improving the film quality in the synthesis of large-area hexagonal boron nitride films (h-BN) for two-dimensional material devices remains a great challenge. The measurement of electrical breakdown dielectric strength (EBD) is one of the most important methods to elucidate the insulating quality of h-BN. In this work, the EBD of high quality exfoliated single-crystal h-BN was investigated using three different electrode structures under different environmental conditions to determine the ideal electrode structure and environment for EBD measurement. A systematic investigation revealed that EBD is not sensitive to contact force or electrode area but strongly depends on the relative humidity during measurement. Once the measurement environment is properly managed, it was found that the EBD values are consistent within experimental error regardless of the electrode structure, which enables the evaluation of the crystallinity of synthesized h-BN at the microscopic and macroscopic level by utilizing the three different electrode structures properly for different purposes. Published by AIP Publishing.
AMER INST PHYSICS, Dec. 2016, APPLIED PHYSICS LETTERS, 109 (25), 253111, English[Refereed]
Scientific journal
Dielectric breakdown has historically been of great interest from the perspectives of fundamental physics and electrical reliability. However, to date, the anisotropy in the dielectric breakdown has not been discussed. Here, we report an anisotropic dielectric breakdown strength (E-BD) for h-BN, which is used as an ideal substrate for two-dimensional (2D) material devices. Under a well-controlled relative humidity, E-BD values in the directions both normal and parallel to the c axis (E-BD perpendicular to c and E-BD parallel to c) were measured to be 3 and 12 MV/cm, respectively. When the crystal structure is changed from sp(3) of cubic-BN (c-BN) to sp(2) of h-BN, E-BD perpendicular to c for h-BN becomes smaller than that for c-BN, while E-BD parallel to c for h-BN drastically increases. Therefore, h-BN can possess a relatively high E-BD concentrated only in the direction parallel to the c axis by conceding a weak bonding direction in the highly anisotropic crystal structure. This explains why the E-BD parallel to c for h-BN is higher than that for diamond. Moreover, the presented EBD value obtained from the high quality bulk h-BN crystal can be regarded as the standard for qualifying the crystallinity of h-BN layers grown via chemical vapor deposition for future electronic applications.
AMER CHEMICAL SOC, Oct. 2016, ACS APPLIED MATERIALS & INTERFACES, 8 (41), 27877 - 27884, English, International magazine[Refereed]
Scientific journal
The key to achieve high-quality van der Waals heterostructure devices made of stacking various two-dimensional (2D) layered materials lies in the clean interface without bubbles and wrinkles. Although polymethylmethacrylate (PMMA) is generally used as a sacrificial transfer film due to its strong adhesion property, it is always dissolved in the solvent after the transfer, resulting in the unavoidable PMMA residue on the top surface. This makes it difficult to locate clean interface areas. In this work, we present a fully dry PMMA transfer of graphene onto h-BN using a heating/cooling system which allows identification of clean interface area for high quality graphene/h-BN heterostructure fabrication. The mechanism lies in the utilization of the large difference in thermal expansion coefficients between polymers (PMMA/PDMS) and inorganic materials (graphene/h-BN substrate) to mechanically peel off PMMA from graphene by the thermal shrinkage of polymers, leaving no PMMA residue on the graphene surface. This method can be applied to all types of 2D layered materials.
IOP PUBLISHING LTD, Dec. 2015, 2D MATERIALS, 2 (4), 041002, English[Refereed]
Scientific journal
Hexagonal boron nitride (BN) is widely used as a substrate and gate insulator for two-dimensional (2D) electronic devices. The studies on insulating properties and electrical reliability of BN itself, however, are quite limited. Here, we report a systematic investigation of the dielectric breakdown characteristics of BN using conductive atomic force microscopy. The electric field strength was found to be similar to 12 MV/cm, which is comparable to that of conventional SiO2 oxides because of the covalent bonding nature of BN. After the hard dielectric breakdown, the BN fractured like a flower into equilateral triangle fragments. However, when the applied voltage was terminated precisely in the middle of the dielectric breakdown, the formation of a hole that did not penetrate to the bottom metal electrode was clearly observed. Subsequent IV measurements of the hole indicated that the BN layer remaining in the hole was still electrically inactive. On the basis of these observations, layer-by-layer breakdown was confirmed for BN with regard to both physical fracture and electrical breakdown. Moreover, statistical analysis of the breakdown voltages using a Weibull plot suggested the anisotropic formation of defects. These results are unique to layered materials and unlike the behavior observed for conventional 3D amorphous oxides.
AMER CHEMICAL SOC, Jan. 2015, ACS NANO, 9 (1), 916 - 921, English, International magazine[Refereed]
Scientific journal
Non-invasive, biomedical devices have the potential to provide important, quantitative data for the assessment of skin diseases and wound healing. Traditional methods either rely on qualitative visual and tactile judgments of a professional and/or data obtained using instrumentation with forms that do not readily allow intimate integration with sensitive skin near a wound site. Here, an electronic sensor platform that can softly and reversibly laminate perilesionally at wounds to provide highly accurate, quantitative data of relevance to the management of surgical wound healing is reported. Clinical studies on patients using thermal sensors and actuators in fractal layouts provide precise time-dependent mapping of temperature and thermal conductivity of the skin near the wounds. Analytical and simulation results establish the fundamentals of the sensing modalities, the mechanics of the system, and strategies for optimized design. The use of this type of epidermal electronics system in a realistic clinical setting with human subjects establishes a set of practical procedures in disinfection, reuse, and protocols for quantitative measurement. The results have the potential to address important unmet needs in chronic wound management.
Lead, WILEY, Oct. 2014, ADVANCED HEALTHCARE MATERIALS, 3 (10), 1597 - 1607, English, International magazine[Refereed]
Scientific journal
Stretchable electronics provide a foundation for applications that exceed the scope of conventional wafer and circuit board technologies due to their unique capacity to integrate with soft materials and curvilinear surfaces. The range of possibilities is predicated on the development of device architectures that simultaneously offer advanced electronic function and compliant mechanics. Here we report that thin films of hard electronic materials patterned in deterministic fractal motifs and bonded to elastomers enable unusual mechanics with important implications in stretchable device design. In particular, we demonstrate the utility of Peano, Greek cross, Vicsek and other fractal constructs to yield space-filling structures of electronic materials, including monocrystalline silicon, for electrophysiological sensors, precision monitors and actuators, and radio frequency antennas. These devices support conformal mounting on the skin and have unique properties such as invisibility under magnetic resonance imaging. The results suggest that fractal-based layouts represent important strategies for hard-soft materials integration.
NATURE PUBLISHING GROUP, Feb. 2014, NATURE COMMUNICATIONS, 5, 3266 - 3266, English, International magazine[Refereed]
Scientific journal
A process for synthesis of nanoparticles using plasma in water generated by a radio frequency of 27.12 MHz is proposed. Tungsten oxide, silver, and gold nanoparticles were produced at 20 kPa through erosion of a metallic electrode exposed to plasma. Characterization of the produced nanoparticles was carried out by XRD, absorption spectrum, and TEM. The nanoparticle sizes were compared with those produced by a similar technique using plasma in liquid. (c) 2013 Elsevier B.V. All rights reserved.
ELSEVIER SCIENCE SA, Nov. 2013, JOURNAL OF ALLOYS AND COMPOUNDS, 578, 148 - 152, English[Refereed]
Scientific journal
The electrical breakdown of microwave plasma in water was investigated between 1 and 30 kPa. The dependency of the ignition power for generating plasma on the size of coaxial electrode was measured. The ignition power decreases with a decrease of the diameter of the inner electrode. The behavior of microwave plasma in water was observed using a high-speed camera. The plasma ignites in a bubble generated by microwave heating. The model for calculating the electric field was created on the basis of the captured images of the bubble just before plasma ignition. The method presented can be used to visualize the electrical field distribution in the bubble. The electric field breakdown was calculated using the measured ignition power. The electric field breakdown of plasma in water is of the same order as gas phase plasma. (C) 2013 Elsevier B.V. All rights reserved.
ELSEVIER SCIENCE BV, Aug. 2013, CURRENT APPLIED PHYSICS, 13 (6), 1050 - 1054, English[Refereed]
Scientific journal
Tungsten trioxide nanoparticles were synthesized from a tungsten wire by plasma generated in water by 2.45 GHz microwaves. The effect of synthesis pressure, power and wire diameter on the formation of nanoparticles and the production rate was investigated. The character of the produced nanoparticles was determined by XRD, absorption spectrum, TEM and particle size distribution. The method proposed in this paper allows control of the nanoparticle size and shape and the optical properties through pressure alone without any additives. In one specific experiment, spherical nanoparticles with a peak diameter of 7 nm were synthesized from a tungsten wire with a diameter of 1 mm by 200 W at 20 kPa at a high production rate of 4 mg/s. Whereas, rhombic cylindrical nanoparticles together with spherical nanoparticles were synthesized with a peak diameter of 13 nm at 101 kPa. In addition, plasma and bubble behavior was observed by high-speed camera. Use of a plate to control the updraft of the bubbles caused the gap between the plate and the coaxial electrode to remain consistently filled with bubbles, and plasma generation continued without pause. (C) 2013 Elsevier B.V. All rights reserved.
ELSEVIER SCIENCE SA, May 2013, JOURNAL OF ALLOYS AND COMPOUNDS, 560, 105 - 110, English[Refereed]
Scientific journal
The erosion of a conventional bare metallic electrode for generation of microwave plasma in liquid was investigated. The spectra of plasma, the surface temperature of the electrode and the erosion rate were measured by a spectroscope, a radiation thermometer and an analytical balance, respectively. The intensity of the spectral lines indicating the erosion of the metallic electrode and erosion rate depends upon the microwave power. To avoid metallic contamination, a coaxial electrode for generating microwave plasma on a dielectric material was developed. The metallic electrode is encased in an alumina closed tube. The side of the alumina closed tube is further covered with an open Teflon tube. It has been confirmed that the electric field is strongest at the point where the alumina closed tube, Teflon opened tube and liquid intersect as determined by the two-dimensional Finite-Difference Time-Domain (2D-FDTD) method. Synthesis of amorphous-carbon deposition in ethanol was conducted. The developed electrode enables synthesis with a smooth deposition. (C) 2011 Elsevier B.V. All rights reserved.
ELSEVIER SCIENCE SA, Jan. 2012, SURFACE & COATINGS TECHNOLOGY, 206 (8-9), 2140 - 2145, English[Refereed]
Scientific journal
Nanoparticles are continuously synthesized from submerged magnesium, zinc, and silver rods 1-2 mm in diameter by microwave plasma in pure water at 20 kPa. Magnesium-hydroxide nanoplates shaped as triangles, truncated triangles or hexagons with 25-125 nm in size are synthesized with a production rate of 60 g h(-1). Zinc-oxide nanoparticles formed as sharp sticks with diameters of 50 nm and lengths of 150-200 nm are synthesized with a production rate of 14 g h(-1). Silver nanoparticles with a diameter of approximately 6 nm are synthesized with a production rate of 0.8 g h(-1). The excitation temperature is estimated by applying the Boltzmann plot method in assumption of local thermodynamic equilibrium. The excitation temperatures obtained from hydrogen, magnesium, and zinc lines are 3300 100 K, 4000 +/- 500K, and 3200 +/- 500 K, respectively. (C) 2011 Elsevier B.V. All rights reserved.
ELSEVIER SCIENCE SA, Dec. 2011, MATERIALS CHEMISTRY AND PHYSICS, 131 (1-2), 425 - 430, English[Refereed]
Scientific journal
Nanoparticles are synthesized efficiently from zinc electrode by microwave plasma in liquid. The nanoparticles synthesized from alcohol resulted in pure zinc particles in the shape of spheres or hexagonal cylinders with a production rate of 3.3 g/h, and energy consumption of 267 J/mg for 1 mg. Whereas the nanoparticles synthesized in pure water are composed of Zn and ZnO. The Zn reacts with water through heat or the passage of time to become ZnO, releasing hydrogen gas. An upper disk placed 1 mm away from the electrode along with the bubbles generated simultaneously with the plasma ignition plays a key role in the synthesis of nanoparticles. (C) 2010 Elsevier B.V. All rights reserved.
ELSEVIER, Jan. 2011, MATERIALS LETTERS, 65 (2), 188 - 190, English[Refereed]
Scientific journal
Plasma was generated in water by irradiation at high frequency of 13.56 MHz, and the behavior of bubbles including the plasma was observed by a high-speed camera. The generation pattern of the bubbles was classified into four types according to liquid temperature and supplied power. Conducting the simulation, the maximum temperature in the bubble was found to be from 3500 K to 4300 K. and the decomposition of water molecule occurred. The gas in the bubble was found to become high ratio of hydrogen. The phenomenon can be regarded as a film boiling of exceptionally high heat flux. (C) 2010 Elsevier Ltd. All rights reserved.
PERGAMON-ELSEVIER SCIENCE LTD, Jul. 2010, INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER, 53 (15-16), 3067 - 3074, English[Refereed]
Scientific journal
The effect of the shape of the electrode to generate 2.45 GHz microwave plasma in pure water is examined. Three variations of a common coaxial electrode are proposed, and compared according to the power required for plasma ignition and the position of plasma ignition in pure water at 6 kPa using a high-speed camera. These coaxial electrodes are calculated using three-dimensional finite-difference time-domain method calculations. The superior shape of coaxial electrode is found to be one with a flat plane on the tip of the inner electrode and dielectric substance located below the tip of the outer electrode. The position of the plasma ignition is related to the shape of the coaxial electrode. By solving the heat-conduction equation of water around the coaxial electrode taking into account the absorption of the microwave energy, the position of the plasma ignition is found to be not where electric field is the largest, but rather where temperature is maximized.
AMER INST PHYSICS, Mar. 2010, JOURNAL OF APPLIED PHYSICS, 107 (6), 063305 - 063308, English[Refereed]
Scientific journal
“In-liquid plasma” is generated inside the bubbles on the tip of an electrode by applying microwave radiation from the electrode. The in-liquid plasma on the tip of an electrode consists of a plasma generation region, vapor phase, bubble interface, and liquid phase. The growth of the bubble, including the plasma, in n-dodecane was observed using a high-speed camera. This was done because the pressure and the temperature surrounding the plasma needed to be clarified for utilizing it in such processes as chemical vapor deposition. The dependence of the bubble growth on the vessel pressure and on the microwave power was clarified, and the internal pressure of the bubbles was calculated by substituting the approximation curve of the observed bubble diameter in the Rayleigh-Plesset equation. The bubbles grow not continuously but intermittently as the plasma region expands and contracts. The growth of the bubbles increases with increase in the microwave power or decrease in the vessel pressure. The value of the internal pressure of the bubbles peaks between 200 and 600 hPa, it increases as the microwave power increases, and the effect of the vessel pressure on it is small. In addition, we measured the temperature surrounding the plasma using a thermocouple. The temperature can be measured vertically from the vapor phase to the liquid phase by moving the thermocouple in that direction. The point where the temperature measurable by the thermocouple reaches a maximum moves away from the tip of the electrode as the microwave power increases. The maximum temperature reaches the approximate saturation temperature of the liquid.
The Heat Transfer Society of Japan, 01 Oct. 2008, Thermal Science and Engineering, 47 (201), 131 - 137, Japanese[Refereed]
Scientific journal
MISC
- 2012, 日本機械学会中国四国支部総会・講演会講演論文集(CD-ROM), 50th水-メタノール混合溶液中でのマイクロ波プラズマによる生成気体に関する研究
- 2011, 日本伝熱シンポジウム講演論文集(CD-ROM), 48thマイクロ波液中プラズマを利用したナノ粒子の合成と対向プレートの影響
- 2010, 日本伝熱シンポジウム講演論文集(CD-ROM), 47thマイクロ波液中プラズマの点火位置に対する熱的影響
- 2010, 日本機械学会中国四国支部・九州支部合同企画講演会講演論文集, 2010液中プラズマ化学蒸着におけるプラズマ泡と基板の相互作用
- 2010, 日本機械学会中国四国支部・九州支部合同企画講演会講演論文集, 2010二層誘電体同軸型電極を利用したマイクロ波液中プラズマ
- 2009, 日本伝熱シンポジウム講演論文集(CD-ROM), 46thGeneration pattern of bubbles and thermal balance of plasma in water
- 2008, 日本伝熱シンポジウム講演論文集(CD-ROM), 45thBehavior of Bubbles and Surrounding Temperature of In-Liquid Plasma
- 2008, Thermal Science and Engineering, 16 (4)Behavior of Bubbles and Surrounding Temperature of In-Liquid Plasma
- 2007, 日本伝熱シンポジウム講演論文集(CD-ROM), 44thBehavior Characteristic of Microwave Plasma in an Organic Solvent
Books etc
- Joint work, NEW DIAMOND, 133, (2019),19-24, 2019, JapaneseBNの絶縁性破壊強さの異方性とその起源
Scholarly book
- ケミカルエンジニアリング, 57(7), (2012), 548-553, 2012液中プラズマによるナノ粒子製造方法
Presentations
- 第70回応用物理学会春季学術講演会, 15 Mar. 2023有機薄膜形成のためのインクジェット法による親水疎水パターニングを用いた液摘挙動制御
- 第70回応用物理学会春季学術講演会, 15 Mar. 2023スパッタリングにより作製したIn5GaZnO10薄膜トランジスタの特性評価
- 第70回応用物理学会春季学術講演会, 15 Mar. 2023層状物質の厚い膜に存在する単層分の厚さの違いを検知する手法
- 第83回応用物理学会秋季学術講演会, 23 Sep. 2022大気中光電子収量分光法による原子比率の異なるInGaZnO 薄膜の仕事関数評価
- 第83回応用物理学会秋季学術講演会, 23 Sep. 2022In5GaZnO10薄膜トランジスタの特性評価
- 第83回応用物理学会秋季学術講演会, 21 Sep. 2022塗布型有機薄膜トランジスタのためのUV/オゾン処理による有機単分子膜の改質
- 第83回応用物理学会秋季学術講演会, 20 Sep. 2022六方晶窒化ホウ素の高電界下における電気伝導と絶縁破壊
[Invited]
- 第69回応用物理学会春季学術講演会, 25 Mar. 2022大気中光電子収量分光法によるInGaZnO薄膜のエネルギーバンド構造解析
Poster presentation
- 第69回応用物理学会春季学術講演会, 22 Mar. 2022金極薄膜を用いた単層h-BNの可視化
Oral presentation
- 2021 MRS FALL MEETING, 07 Dec. 2021Organic thin-film transistors for high performance logic circuits: Realization of short channel, high mobility, low contact resistance and threshold voltage control
[Invited]
- 薄膜材料デバイス研究会 第18回研究集会, Nov. 2021Visualization of an alkanethiol monolayer via reflected light microscope
- 応用物理学会関西支部 2021年度第２回講演会, Oct. 2021塗布法による有機半導体薄膜の製膜において 2度塗りした際の薄膜形成メカニズム
- 応用物理学会関西支部 2021年度第２回講演会, Oct. 2021疎水性単分子膜を修飾した基板上への塗布法を用いた有機半導体薄膜形成技術
- The International Conference on Flexible and Printed Electronics (ICFPE), Sep. 2021Organic monolayers modified by ultraviolet-ozone for solution-processed organic thin-film transistors
- 応用物理学会関西支部 2021年度第１回講演会, Apr. 2021光学顕微鏡による的異方性を持つ単分子有機薄膜の観察と画像処理解析
- 応用物理学会関西支部 2021年度第１回講演会, Apr. 2021光電子収量分法による酸素プラズマ処理したSiO2絶縁膜表面のエネルギー準位分析
- 応用物理学会関西支部 2021年度第１回講演会, Apr. 2021撥水性基板上にスピンコート法を用いて作製した有機薄膜トランラジタの評価
- IEEE EDS Kansai Chapter 第20回「関西コロキアム電子デバイスワークショップ」, Nov. 2020Bottom-contact pentacene thin-film transistor with threshold voltages controlled by oxygen plasma treatment
- 薄膜材料デバイス研究会 第17回研究集会, Nov. 2020酸素プラズマ処理により生じる有機半導体／ゲート絶縁膜界面準位のエネルギー分布
- 39th Electronic Materials Symposium, Oct. 2020Highly thermal-stable monolayers formed on a gold surface using benzenedithiol
- 39th Electronic Materials Symposium, Oct. 2020Evaluation of carrier mobility in organic metal-oxide-semiconductor capacitors
- 第67回応用物理学会春季学術講演会, Mar. 2020偏光顕微鏡を用いた単層DPh-DNTT二次元核の方位決定
- 第67回応用物理学会春季学術講演会, Mar. 2020酸素プラズマ処理が与える有機半導体/絶縁膜界面準位への影響
- 薄膜材料デバイス研究会 第16回研究集会, Nov. 2019フルオロベンゼンチオールを電極表面に修飾した有機薄膜トランジスタ
- 38th Electronic Materials Symposium, Oct. 2019Statistical study of shape for submonolayer 2D islands of DPh-DNTT prepared by vacuum deposition
- 第80回応用物理学会学術講演会, Sep. 2019金表面に形成したベンゼンジチオール単分子膜の耐熱性評価
- 第80回応用物理学会学術講演会, Sep. 2019MOSキャパシタ構造を利用した有機半導体中のキャリア移動度評価
- 第80回応用物理学会学術講演会, Sep. 2019単層 DPh-DNTT の2次元アイランドにおける異方性
- International Conference on Solid State Devices and Materials (SSDM), Sep. 2019Bottom-contact pentacene thin-film transistor with threshold voltages controlled by oxygen plasma treatment
- 応用物理学会関西支部 2019年度第１回講演会, Jun. 2019有機薄膜トランジスタにおける酸素プラズマを用いたパターニング
- 応用物理学会関西支部 2019年度第１回講演会, Jun. 2019UV/ozone処理を用いた熱酸化膜上単分子膜の被覆率操作
- 10th International Conference on Molecular Electronics and Bioelectronics (M&BE 10), Jun. 2019The formation of a mixed monolayer on a gold surface toward surface property control
- 10th International Conference on Molecular Electronics and Bioelectronics (M&BE 10), Jun. 2019High thermal stability of the benzenedithiol monolayer formed on a gold surface
- 10th International Conference on Molecular Electronics and Bioelectronics (M&BE 10), Jun. 2019Surface properties of oriented polytetrafluoroethylene films with a micrometer pitch
- Compound Semiconducotr Week (csw2019), May 2019, English, International conferenceVoltage and frequency dependence of capacitance characteristics in organic MOS capacitors
Poster presentation
- Compound Semiconducotr Week (csw2019), May 2019, English, International conferenceThin-film transistors based on copper phthalocyanine deposited on a gate dielectric rubbed with poly(tetrafluoroethylene)
Poster presentation
- Compound Semiconducotr Week (csw2019), May 2019, English, International conferenceNucleation and shape of 2D islands of DPh-DNTT thin-films prepared by vacuum evaporation
Oral presentation
- 第67応用物理学関係連合講演会, Mar. 2019酸素プラズマ処理が与える有機半導体/絶縁膜界面準位への影響
- 第67応用物理学関係連合講演会, Mar. 2019偏光顕微鏡を用いた単層DPh-DNTT二次元核の方位決定
- 第66回応用物理学会春季学術講演会, Mar. 2019, Japanese, Domestic conference有機MOSキャパシタの電圧・周波数特性解析
Oral presentation
- 第66回応用物理学会春季学術講演会, Mar. 2019, Japanese, Domestic conference真空蒸着法におけるDNTTとその誘導体の核形成機構
Oral presentation
- 第66回応用物理学会春季学術講演会, Mar. 2019, Japanese, Domestic conference酸素プラズマ処理によるボトムコンタクト型有機トランジスタの閾値電圧制御
Poster presentation
- 第15回薄膜材料デバイス研究会, Nov. 2018, Japanese, Domestic conferenceポリテトラフルオロエチレン配向膜を有する銅フタロシアニン薄膜トランジスタ
Poster presentation
- 第15回薄膜材料デバイス研究会, Nov. 2018, Japanese, Domestic conferenceフルオロベンゼンチオール修飾による金表面の制御と有機トランジスタ応用
Keynote oral presentation
- 第79回応用物理学会学術講演会, Sep. 2018, Japanese, Domestic conference有機薄膜トランジスタへの応用に向けたフルオロベンゼンチオール表面修飾による金電極の仕事関数制御
Poster presentation
- 第79回応用物理学会学術講演会, Sep. 2018, Japanese, Domestic conference有機薄膜トランジスタにおける酸素プラズマ処理による閾値電圧シフトの起源
Poster presentation
- 第79回応用物理学会学術講演会, Sep. 2018, Japanese, Domestic conference真空蒸着法におけるDPh-DNTT薄膜の成長機構
Oral presentation
- International Conference on Solid State Devices and Materials (SSDM), Sep. 2018, English, International conferenceLogic circuits consisting of pentacene thin-film transistors with controlled threshold voltages
Oral presentation
- International Conference on Solid State Devices and Materials (SSDM), Sep. 2018, English, International conferenceGrowth mechanism and electrical characterization of DPh-DNTT films prepared by vacuum deposition
Oral presentation
- 2nd Bilateral Kobe-Kiel Workshop, Sep. 2018, English, International conferenceDielectric breakdown of h-BN and growth mechanism of DPh-DNTT
Oral presentation
- 3rd Bilateral Workshop on Research Exchange between National Taiwan University and Kobe University, Jul. 2018, English, International conferenceThermal resistivity of copper phthalocyanine based thin-film transistors
Poster presentation
- 3rd Bilateral Workshop on Research Exchange between National Taiwan University and Kobe University, Jul. 2018, English, International conferenceLayered materials for electronics
Oral presentation
- 3rd Bilateral Workshop on Research Exchange between National Taiwan University and Kobe University, Jul. 2018, English, International conferenceElectrode-surface modification for high-performance organic thin-film transistors
Poster presentation
- 第65応用物理学関係連合講演会, Mar. 2018, Japanese, Domestic conferenceボトムコンタクト型有機薄膜トランジスタにおける閾値電圧制御
Poster presentation
- 第65応用物理学関係連合講演会, Mar. 2018, Japanese, Domestic conferenceキャパシタンス測定による有機トランジスタの寄生抵抗評価
Oral presentation
- 第65回応用物理学会春季学術講演会, Mar. 2018, Japanese, Domestic conferenceDPh-DNTT 薄膜トランジスタの遮断周波数測定
Poster presentation
- 2016 COMPOUND SEMICONDUCTOR WEEK (CSW) INCLUDES 28TH INTERNATIONAL CONFERENCE ON INDIUM PHOSPHIDE & RELATED MATERIALS (IPRM) & 43RD INTERNATIONAL SYMPOSIUM ON COMPOUND SEMICONDUCTORS (ISCS), 2016, English, IEEEDielectric breakdown of layered insulator
- The Proceedings of Conference of Chugoku-Shikoku Branch, 2012, Japanese, The Japan Society of Mechanical Engineers1317 Study on gas production by microwave plasma in water-methanol mixture.
- The Proceedings of Conference of Chugoku-Shikoku Branch, 2012, Japanese, The Japan Society of Mechanical Engineers1314 Nanoparticles Continuous Synthesis Applying Microwave Plasma in Liquid and Effect of System Pressure
- The Proceedings of Conference of Chugoku-Shikoku Branch, 2011, Japanese, The Japan Society of Mechanical Engineers1407 An investigation of the suitable substrate for synthesizingdiamond by in-liquid plasma chemical deposition
- The Proceedings of Conference of Chugoku-Shikoku Branch, 2011, Japanese, The Japan Society of Mechanical Engineers1408 An investigation ofthe optimum experimental condition forsynthesizing diamond by in-Iiquid plasma chemical deposition
- Proceedings of National Heat Transfer Symposium, 2011, Japanese, The Heat Transfer Society of Japan, 液体中で亜鉛の電極を利用しマイクロ波プラズマを発生させて電極を原料としたナノ粒子の合成を行った。エタノール中でプラズマを発生させると10-200nmの六角柱または球体の亜鉛ナノ粒子が合成され、純水中で発生させると亜鉛ナノ粒子と酸化亜鉛ナノ粒子が凝集した約200nmの花びら型をした粒子が合成された。また、電極上部に設置された金属プレートの直径と位置を変え、ナノ粒子の合成に及ぼす影響を調べた。ナノ粒子の合成速度は金属プレートの直径が大きいほど、位置が電極先端に近いほど大きくなった。投入電力が230Wの場合、合成速度は5g/hourとなった。さらに、銅の電極を利用し放電開始電力を調べた。放電開始電力は金属プレートの位置が近いほど小さくなった。Nanoparticle Synthesis Applying Microwave Plasma in Liquid and Effect of Counter Plate
- 日本機械学会中国四国支部・九州支部合同企画講演会講演論文集, 01 Oct. 2010, Japanese二層誘電体同軸型電極を利用したマイクロ波液中プラズマ
- 日本機械学会中国四国支部・九州支部合同企画講演会講演論文集, 01 Oct. 2010, Japanese液中プラズマ化学蒸着におけるプラズマ泡と基板の相互作用
- Proceedings of National Heat Transfer Symposium, 2010, Japanese, The Heat Transfer Society of Japan, 純水中に発生するマイクロ波液中プラズマの点火位置を高速度カメラで観察した。また、3D-FDTD法を用いて電極表面の電界を計算し、マイクロ波によって加熱される液体が吸収する熱量を計算した。この熱量を使って電極周辺の液体の温度計算した結果、プラズマが発生する電極表面の電界強度の最も高い位置と、最も温度が高い位置は必ずしも一致しないことが明らかになった。また、実験から測定したプラズマの点火位置と数値計算によって求めた最も温度の高い地点が一致した。Thermal Influence on Ignition Position of Microwave Plasma in Liquid
- The Proceedings of Conference of Chugoku-Shikoku Branch, 2009, Japanese, The Japan Society of Mechanical Engineers403 Influence of Electrode Shape on Electrical Breakdown of Microwave In-liquid Plasma
- Proceedings of National Heat Transfer Symposium, 2009, Japanese, The Heat Transfer Society of Japan, 純水中に高周波を照射する電極を設置し，電極先端でプラズマを発生させる．高速度カメラでプラズマを内包する気泡の挙動を観察する．気泡の生成様式は，水温と供給電力により4つに分類され，加熱沸騰の場合との比較を行った．供給電力に対して，水温の上昇に消費される熱は約90%，蒸発として消費される熱は約10%，気泡表面から水中へと伝導される熱は約30%，さらに，化学反応により消費される熱は1%以下となることがわかった．Generation Pattern of Bubbles and Thermal Balance of Plasma in Water
- HT2008: PROCEEDINGS OF THE ASME SUMMER HEAT TRANSFER CONFERENCE, VOL 1, 2009, English, AMER SOC MECHANICAL ENGINEERS, The plasma in liquid is generated by applying High-Frequency (HF) irradiation of 27.12 MHz or Microwave (MW) irradiation of 2.45 GHz from an electrode, namely, a monopole-antenna electrode inserted into a reactor vessel. n-dodecane, methanol, and water are used as test liquids. The glow discharge plasma can be kept in spite of atmospheric pressure due to the cooling effect of liquid itself The light emission from the plasma changes substantially according to the behavior of the bubble. The present Chemical Vapor Deposition (CVD) process also enabled simultaneous production of hydrogen gas and the synthesis of the Carbon Nano-Tubes (CNTs) in hydrocarbon liquids. The actual production of hydrogen per unit energy by this process corresponds to approximately 1% of that by conventional steam reforming method and about 32% of that by the alkaline water electrolysis. Moreover, this process can make the solid carbon of about 14 g/h at the same time.Simultaneous Production of Hydrogen and CNTs by In-Liquid Plasma, and Its Discharge Characteristics
- Proceedings of National Heat Transfer Symposium, 2008, Japanese, The Heat Transfer Society of Japan, 液中プラズマは気相プラズマとは異なる特徴をもち，応用研究は活発に行われている．一方，基礎的な発生メカニズムや物性に関する研究報告は少ない．本研究では，プラズマ発生と同時に，プラズマを内包しながら発生し成長する泡の挙動を高速度ビデオカメラで撮影し，画像から気泡内部の圧力を求め，熱電対を用いてプラズマ周辺の温度を測定する．液中プラズマの気泡は系圧力が小さいほど大きく成長し，気泡が膨張，収縮する周期が長くなる．周辺温度はプラズマが消費するエネルギー量が大きく，系圧力が大きいほど上昇する．Behavior of Bubbles and Surrounding Temperature of In-Liquid Plasma
- 日本伝熱シンポジウム講演論文集(CD-ROM), 2007, JapaneseBehavior Characteristic of Microwave Plasma in an Organic Solvent
- IEEE EDS Kansai Chapter 第19回「関西コロキアム電子デバイスワークショップ」Logic Circuits Consisting of Pentacene Thin-Film Transistors with Controlled Threshold Voltages
Research Projects
- 日本学術振興会, 科学研究費助成事業 基盤研究(C), 基盤研究(C), 神戸大学, 01 Apr. 2021 - 31 Mar. 2024その場観察法を用いた有機半導体薄膜の成長メカニズムの解明
- 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, 01 Apr. 2019 - 31 Mar. 2022Fundamental development for realization of high-performance organic transistors based on molecular orientation and interface control
本研究では実用に耐えうる低電圧，高速動作可能な有機トランジスタの開発を目指して，それを実現するための基盤技術開発に取り組んでいる．特に，[A]有機薄膜の配向性，[B]金属表面の単分子膜，[C]酸化物の表面処理とドーピング，[D]有機半導体へのドーピング，[E]顕微ラマン分光に関わる技術を駆使して，目標とする特性を実現することを目指している．[A]有機薄膜の配向性については，高移動度かつ熱耐性にすぐれるDPh-DNTTという材料について，真空蒸着の際にlayer-by-layer成長をすることを確認し，かつ，高移動度化に有利となる大きなグレインが得られる条件を見出した．また，配向制御に利用するテフロン板をつかったラビング膜の作製も開始し，最適な条件を見しだしつつある．[B]金属表面の単分子膜については，量子化学計算により予測した，分極の大きい分子を表面修飾に用いることにより，より広い範囲で仕事関数を制御することに成功した．[C]酸化物の表面処理とドーピングについては，酸素プラズマ処理による閾値電圧制御について，シリコン熱酸化膜の価電子帯上端付近に，エネルギー準位が形成することを見出した．[D]有機半導体へのドーピングはフェルミ準位制御を目的としているが，フェルミ準位の測定に向けて，閾値電圧制御した有機MOSキャパシタのインピーダンス分光に取り組んでおり，測定方法を確立しつつある．[E]顕微ラマン分光については，まずは，DPh-DNTT薄膜の測定に取り組み，膜厚に依存してラマンスペクトルの強度が変化することを確認した．また，量子化学計算により予測されるピークとの対応付を行った．
- 日本学術振興会, 科学研究費助成事業 若手研究, 若手研究, 神戸大学, 01 Apr. 2019 - 31 Mar. 2021多結晶有機半導体薄膜におけるキャリア散乱と輸送特性の向上に関する研究
有機半導体デバイスの実用化にはキャリア移動度の向上が必要である。移動度の低下は結晶粒界で起こるため、デバイスの有機半導体層の粒界を少なくすることが有効であるが、今だ、商用利用可能な技術は確立されていない。真空蒸着法は現状の半導体シリコンデバイスでも使われている一般的な薄膜の作製方法であり、有機半導体薄膜への技術転用が容易であるが、真空蒸着法では有機半導体薄膜が多結晶膜になってしまうので、結晶粒を大きくする蒸着手法を見出すことが重要である。結晶粒は結晶核から成長するので、製膜開始直後の結晶核の核密度を減少し、形成過程を制御することが重要であるため、薄膜の初期成長に関して調査を行った。 有機半導体デバイスに使われる低分子材料は基板から層状に一層ずつ成長していく性質があるが、1層目が完成する前に蒸着を止めて、その形や密度を調べた。結晶核の密度は、蒸着前の基板の表面処理や蒸着中の基板温度により変わることが分かった、一方で、蒸着条件にかかわらず、結晶核の形は核密度が減少するほどフラクタル状に複雑な形になった。これらは基板に到達した有機分子が基板の表面で起こす表面拡散と、既存の安定した結晶核に取り込まれた有機分子が核の周囲を拡散するエッジ拡散によって説明が可能である。表面拡散が大きいほど核密度が減少し、エッジ拡散が大きいほど単純な形の結晶核が形成される。様々な蒸着条件で実験を繰り返し、これらの関係を分析した結果、エッジ拡散は基板の表面処理に依存しないことが分かり、材料固有のもつ物性値のようにみなせることが分かった。デバイス応用を考える上では、エッジ拡散は大きい方が好ましく、これらの値は分子間の相互作用によって決まるために、近年研究が進んでいる細長い棒状の低分子の構造において、エッジ拡散の観点から骨格や側鎖の材料設計を行うことが重要であると考えられる。
- 学術研究助成基金助成金／若手研究(B), Apr. 2017 - Mar. 2019, Principal investigator
Competitive research funding
- Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research Grant-in-Aid for Research Activity Start-up, Grant-in-Aid for Research Activity Start-up, The University of Tokyo, 29 Aug. 2014 - 31 Mar. 2016
Hexagonal boron nitride (h-BN) is considered as ideal substrate for 2D material devises. However, the reliability of insulating properties of h-BN itself has not been clarified yet. The anisotropic dielectric breakdown of h-BN has been studied. We have found that the dielectric breakdown in c axis direction using a conductive atomic force microscope proceeded in the layer-by-layer manner. The obtained dielectric field strength was ~12 MV/cm, which is comparable to the conventional SiO2. On the other hand, metal electrodes were fabricated on the h-BN surface to measure the dielectric field strength in a direction perpendicular to c axis. The dielectric field strength was estimated to be 3 MV/cm, which is the smaller than that in c axis direction.