Takatoshi Yamada

National Institute of Advanced Industrial Science and Technology

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Ken Okano

International Christian University

100

Tomoaki Masuzawa

Shizuoka University

Ichitaro Saito

International Christian University

Masataka Hasegawa

National Institute of Advanced Industrial Science and Technology

Yuki Okigawa

National Institute of Advanced Industrial Science and Technology

Hisato Yamaguchi

Los Alamos National Laboratory

Yuki Kudo

Toshiba (Japan)

Shinichi Shikata

National Institute of Advanced Industrial Science and Technology

Daniel H. C. Chua

National University of Singapore

Yuji Takakuwa

Tohoku University

Cooperative Institutions

The University of Tokyo

415

National Astronomical Observatory of Japan

203

Kyoto University

162

Tohoku University

145

National Institute of Advanced Industrial Science and Technology

119

Osaka University

102

Nagoya University

Tokyo Institute of Technology

Kavli Institute for the Physics and Mathematics of the Universe

Tokyo University of Science

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Gas Barrier Properties of Chemical Vapor-Deposited Graphene to Oxygen Imparted with Sub-electronvolt Kinetic Energy

The Journal of Physical Chemistry Letters (2020)

Shuichi Ogawa Hisato Yamaguchi Edward F. Holby Takatoshi Yamada Akitaka Yoshigoe

Graphene gas-barrier performance holds great interest from both scientific and technological perspectives. Using in situ synchrotron X-ray photoelectron spectroscopy, we demonstrate that chemical vapor-deposited monolayer graphene loses its gas-barrier performance almost completely when oxygen molecules are imparted with sub-electronvolt kinetic energy but retains its gas-barrier performance when the molecules are not energized. The permeation process is nondestructive. Molecular dynamics-based simulation suggests kinetic energy-mediated chemical reactions catalyzed by common graphene defects as a responsible mechanism.

10.1021/acs.jpclett.0c02112

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Citations (5)

A high performance IGBT with new n+buffer structure

H. Takahashi Yoji Ishimura Chiaki Yokoyama H. Hagino Takatoshi Yamada

An advanced IGBT with a new n+buffer structure has been developed. The new n+buffer structure is that some n+buried layers are formed at the boundary between a p+substrate and a n+buffer layer. The concentration of the n+buried layers is almost the same as that of the p+substrate. The fabrication of the IGBT with the new n+buffer structure used a 3rd gen 600 V/100 A chip. Taking the VVVF inverter as an application, total power loss generated was about 12% less compared to the conventional IGBT, only changing the n+buffer structure. And the short circuit safe operating area of the new IGBT was almost similar to the conventional IGBT. Moreover, we discussed differences between the new IGBT and the conventional IGBT using a 3D simulator, DAVINCI.

Insulated-gate bipolar transistor

Buffer (optical fiber)

10.1109/ispsd.1995.515084

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Citations (10)

Graphene synthesis from poly(methyl methacrylate) by microwave plasma treatment at low temperature

Takatoshi Yamada Masatou Ishihara Yuki Okigawa Masataka Hasegawa

A low temperature synthesis of graphene from poly(methyl methacrylate) by surface wave microwave plasma treatment was developed. Single- or double-layer graphene was formed. Raman signal mappings indicated that the obtained graphene consisted of small size of flakes and each flake connected to form continuous graphene film. In results of Hall effects measurements, the highest hole mobility was 560cm2/Vs and the lowest sheet resistance of 1000Ω/sq were obtained.

Poly(N-isopropylacrylamide)

10.1109/inec.2014.7460442

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Characterization of Photochemical Reaction in Photosensitive Printing Plates.

Journal of Photopolymer Science and Technology (2002)

Keizo Kawahara Takatoshi Yamada Yasuyuki Okazaki Satoshi Imahashi Yoshimitsu Sakaguchi

Photochemical reaction in three different water-developable flexographic printing plates was characterized. The distribution of photochemical reaction in the direction of thickness was evaluated by utilizing 13C NMR and IR (ATR) measurements, and the results obtained showed that the distribution of reaction as well as the overall reaction in the printing plates depends on the plate compositions. 1H NMR analysis for soxhlet extracts of exposed samples showed that the reactivity of monomers depends on its structure and molecular weight in relating to a specified phase condition of the composition.

Reactivity

Characterization

Reaction conditions

Molar mass distribution

Proton NMR

10.2494/photopolymer.15.59

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Citations (2)

Electron emission from N-doped diamond doped with dimethylurea

Yuki Kudo Yu Sato Tomoaki Masuzawa Takatoshi Yamada Ichitaro Saito

We have been focusing on fabricating a photodetector that consists of a diamond cold cathode and an amorphous selenium (a-Se) photoconductor, which is one of the practical applications of a cold cathode. We have previously succeeded in achieving a proto-type photodetector of which a heavily nitrogen (N)-doped diamond was used as the cold cathode, and the results indeed showed a low operation voltage. This heavily N-doped diamond was fabricated using urea as a dopant and the saturated solution of urea and methanol was diluted with acetone and used as a reactant gas. Although this diamond cathode exhibited low extraction voltage, the reproducibility of obtaining low threshold cathode was not as high as expected and the improvement should be considered for wider extensive application. In order to solve this problem, dimethylurea was introduced due to its structure more similar to diamond and soluble in acetone, where urea is insoluble without the use of methanol. Dimethylurea-saturated solutions of acetone diluted at a ratio of 1:100, 1:1000, and 1:10000 with acetone is vaporized and used as the reactant gas and diamond is grown on a silicon substrate by hot filament CVD method. The N/C ratio in the CVD apparatus is 1000 ppm, 100 ppm and 10 ppm respectively. The electron emission characteristics of N-doped diamond doped with dimethylurea are then measured. The experiment was performed under a base pressure of 4 x 10 ^-6 Pa. Anode-cathode distance is fixed to 50mum and the current versus voltage (I-V) characteristics are measured.

10.1109/ivnc.2009.5271641

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Over 1000 V n-ch LDMOSFET and p-ch LIGBT with JI RESURF structure and multiple floating field plate

Takeshi Terashima J. Yamashita Takatoshi Yamada

A new 1500 V n-ch LDMOSFET and a new 1200 V p-ch LIGBT using JI/RESURF structures with a new surface electric field relaxation structure, MFFP, and n+/n-buried layer are described. On resistance of the n-ch LDMOSFET is about 700 /spl Omega/ and it has 800 V/100 mA switching capabilities. The p-ch LIGBT has a p-LDD structure. On resistance of this device is 1600 /spl Omega/ and that value may be reduced to one third compared to a p-ch LDMOSFET of same chip size.

Power MOSFET

10.1109/ispsd.1995.515081

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Citations (21)

Optical properties and microstructures of inorganic wave plates prepared by serial bideposition

Journal of Nanophotonics (2014)

Nobuyuki Koike Koji Sasaki Takatoshi Yamada Naoki Hanashima Akio Takada

We investigated the optical characteristics and microstructures of wave plates composed of Ta2O5(100−x)+TiO2(x) and prepared by the so-called serial bideposition technique. While a single-layer film prepared by conventional oblique deposition technique has a tilted columnar structure (i.e., tilted optical axis), a serial bideposition film has a narrow, long columnar structure; this ensures that the optical axis of the film is along the quasinormal to the substrate, thus reducing haze. The influence of using additives with Ta2O5 was investigated as well. It was found that additive TiO2 improves optical transmittance at shorter wavelengths. For verifying the advantage of this type of wave plates, quarter wave plates with optimized TiO2 content were fabricated and their optical performance and reliability were evaluated against those of organic-type wave plates. The results show that the inorganic wave plate prepared by serial bideposition is advantageous for applications where high-transmittance and high-temperature durability are essential.

Optical coating

Haze

10.1117/1.jnp.8.083991

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A Case Report of Hepatocellular Carcinoma Invading into Gall Bladder.

The Japanese Journal of Gastroenterological Surgery (2001)

Kyohei Kai Shizou Satoh Youichi Sibuya Takatoshi Yamada Akira Nakashima

胆嚢内出血による腹痛により発症した肝細胞癌の胆嚢浸潤例を経験したので報告する. 症例は60歳の男性. 突然の上腹部痛にて近医受診. 入院経過観察中に, CTで肝内側区域に低吸収域を認め, 症状軽快しないため当科紹介された. 画像診断で胆嚢腫瘍の肝浸潤に胆嚢内出血, 肝内出血を伴ったものを疑い開腹手術を行った. 胆嚢, 肝前下, 内側区域, 胃前庭部を一塊として摘出した. 病理組織診断では低分化型肝細胞癌の胆嚢内浸潤に伴う胆嚢内出血, 肝内出血と診断された. 術後早期に残肝多発再発を認め, 以後腫瘍の急速増大で術後54日目に肝不全で死亡した. 胆嚢浸潤肝細胞癌の報告例は, 本例を含め7例であったが, その予後は極めて不良であった.

10.5833/jjgs.34.1303

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Electron emission mechanism of diamond characterized using combined x-ray photoelectron spectroscopy/ultraviolet photoelectron spectroscopy/field emission spectroscopy system

Applied Physics Letters (2006)

Hisato Yamaguchi Takatoshi Yamada Masato Kudo Yuji Takakuwa Ken Okano

Clarification on electron emission mechanism of diamond is one essential approach to realize the clear vision of vacuum nanoelectronics. Electric field of less than 5V∕μm is enough to extract electrons from diamond, whereas field of one to two orders of magnitude higher is needed to extract electrons from conventional metal emitter tips. Diamond has various advantages as an electron emitter in addition to the low-threshold voltage, such as negative electron affinity and high thermal conductivity. The difficulty in clarification of electron emission mechanism is the factor preventing diamond from being used in a practical way. In this study, combined spectroscopy of x-ray photoelectron spectroscopy/ultraviolet photoelectron spectroscopy/field emission spectroscopy was performed to characterize the electron emission mechanism of diamond. The results indicated the first successful observation of applied voltage dependence on the origin of field-emitted electrons.

Ultraviolet photoelectron spectroscopy

Electron spectroscopy

10.1063/1.2200229

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Citations (23)

Temperature dependence on electron emission of boron-doped diamond

Takatoshi Yamada Atsuhito Sawabe Y. Suzuki Ken Okano

Temperature dependence on electron emission of B-doped CVD diamond is investigated in order to understand the electron emission properties. Films are deposited on Si substrate using dc plasma CVD. The obtained films are identified as polycrystalline diamond using XRD, RHEED, EELS and Raman spectroscopy. The threshold voltage in the electron emission properties becomes lower as increasing the temperature.

10.1109/ivmc.2001.939772

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