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Journal Articles

Poly(ether ether ketone) (PEEK)-based graft-type polymer electrolyte membranes having high crystallinity for high conducting and mechanical properties under various humidified conditions

Hamada, Takashi; Hasegawa, Shin; Fukasawa, Hideyuki*; Sawada, Shinichi; Koshikawa, Hiroshi; Miyashita, Atsumi; Maekawa, Yasunari

Journal of Materials Chemistry A, 3(42), p.20983 - 20991, 2015/11

 Times Cited Count:23 Percentile:31.64(Chemistry, Physical)

no abstracts in English

Journal Articles

Structural and gasochromic properties of WO$$_{3}$$ films prepared by reactive sputtering deposition

Yamamoto, Shunya; Hakoda, Teruyuki; Miyashita, Atsumi; Yoshikawa, Masahito

Materials Research Express (Internet), 2(2), p.026401_1 - 026401_8, 2015/02

 Times Cited Count:2 Percentile:89.99(Materials Science, Multidisciplinary)

The effects of deposition temperature and film thickness on the structural and gasochromic properties of tungsten trioxide films used for the optical detection of diluted cyclohexane have been investigated. The tungsten trioxide films were prepared on SiO$$_{2}$$ substrates by magnetron sputtering, with the deposition temperature ranging from 300 to 550$$^{circ}$$C in an Ar and O$$_{2}$$ gas mixture. The gasochromic properties of the films, coated with a catalytic Pt layer, were examined by exposing them up to 5% cyclohexane in N$$_{2}$$ gas. We found that (001)-oriented monoclinic tungsten trioxide films, with a columnar structure, grew at deposition temperatures between 400 and 450$$^{circ}$$C. The gasochromic characterization of the tungsten trioxide films revealed that (001)-oriented tungsten trioxide films, with cauliflower-like surface morphology, were appropriate for the optical detection of cyclohexane.

Journal Articles

Creation of database of radiation resistance on polymer materials and equipment

Shimada, Akihiko; Sugimoto, Masaki; Miyashita, Atsumi; Yoshikawa, Masahito

JAEA-Review 2013-059, JAEA Takasaki Annual Report 2012, P. 29, 2014/03

Recovery from the accident at Tokyo Electric Power Company Fukushima Dai-ichi Nuclear Power Plant (NPP) is a matter of great urgency. In order to realize safe and secure operation for decontamination and decommissioning of NPP, it is indispensable to use equipments with sufficient radiation resistance (RR). In JAEA as well as other agency, various studies on RR of various materials and equipments have been conducted and a number of reports and papers have been published. Then, we started construction of a database named as "Database of Radiation Resistance on Polymer Materials and Equipments" and announced this database in a press release on June 1, 2012. At present, the database includes 878 data of materials, which are consisted of 423 data of polymer materials, 223 data of equipments and parts, 103 data of oils, fats and paintcoatings and 129 data of organic composite materials. The database will be extended and expected to be utilized for safe and secure operation.

Journal Articles

Atomic and electronic structure analysis of the interface between $$a$$-SiO$$_{2}$$ and 4H-SiC(11-20)

Miyashita, Atsumi; Yoshikawa, Masahito

JAEA-Review 2013-059, JAEA Takasaki Annual Report 2012, P. 11, 2014/03

no abstracts in English

Journal Articles

Mass production and quality control of Nb$$_3$$Sn superconducting strands for ITER toroidal field coils

Nabara, Yoshihiro; Nunoya, Yoshihiko; Isono, Takaaki; Hamada, Kazuya; Uno, Yasuhiro; Takahashi, Yoshikazu; Nakajima, Hideo; Tsuzuku, Seiji*; Tagawa, Kohei*; Miyashita, Katsumi*; et al.

Teion Kogaku, 47(3), p.140 - 146, 2012/03

no abstracts in English

Journal Articles

Simulation for SiC power electronic device developments

Onuma, Toshiharu*; Miyashita, Atsumi; Yoshikawa, Masahito; Tsuchida, Hidekazu*; Iwasawa, Misako*

Heisei-21-Nendo Sentan Kenkyu Shisetsu Kyoyo Sokushin Jigyo "Chikyu Shimyureta Sangyo Senryaku Riyo Puroguramu" Riyo Seika Hokokusho, p.21 - 27, 2010/07

Silicon carbide, being a wide-band-gap semiconductor, is an attractive material in the development of electronic devices operated under extreme conditions such as high power, high temperature, and high radiation. SiC is particularly attractive for use in MOS technology because among the compound semiconductors only silicon carbide has the thermal oxide SiO$$_2$$, which is a good insulator. However, it is known that SiO$$_2$$/SiC interfaces have a higher density of interface traps than SiO$$_2$$/Si interfaces and that the channel mobility of MOS devices is much lower than theoretically expected values. In order to improve these characteristics, it is important to understand the thermal oxidation process at the SiO$$_2$$/SiC interface. We performed large-scale first-principles molecular dynamics simulations of the SiO$$_2$$/SiC interface oxidation process. We also performed large-scale first-principles molecular dynamics simulations to generate amorphous SiO$$_2$$/SiC interface.

Journal Articles

Effect of tungsten valences on gasochromic coloration in tungsten oxide thin films

Takano, Katsuyoshi; Inoue, Aichi; Yamamoto, Shunya; Miyashita, Atsumi; Yoshikawa, Masahito

Transactions of the Materials Research Society of Japan, 32(1), p.159 - 162, 2007/03

Ion irradiations with $$^4$$He$$^+$$ at 350 keV were performed for the tungsten tri-oxide (WO$$_3$$) films. Gasochromic coloration of the irradiated films was observed by a measurement of optical transmittance with the expose of 1 % hydrogen. The extent of coloration level of the irradiated film with the fluence of $$1 times 10^{17}$$ ions/sm$$^2$$ is 7.5 times lager than that of non-irradiated film. W 4$$f$$ photoemission spectra for the films were measured by X-ray photoelectron spectroscopy. From the fitting analysis for the spectra, the non-irradiated film has only W$$^{6+}$$. In the irradiated film with the fluence of $$1 times 10^{17}$$ ions/sm$$^2$$, it is estimated that 17 % and 4 % of the amount of W$$^{6+}$$ change into W$$^{5+}$$ and W$$^{4+}$$, respectively. The improvement of the gasochromic coloration of the irradiated WO$$_3$$ films relates to the increment of oxygen deficient tungstens induced by the irradiation.

Journal Articles

Generation of amorphous SiO$$_{2}$$/SiC interface structure by the first-principles molecular dynamics simulation

Miyashita, Atsumi; Onuma, Toshiharu*; Iwasawa, Misako*; Tsuchida, Hidekazu*; Yoshikawa, Masahito

Materials Science Forum, 556-557, p.521 - 524, 2007/00

SiC semiconductor devices are expected to be used in severe environments. However, SiC devices don't present the theoretically expected performance. This is considered to be attributed to the SiO$$_{2}$$/SiC interface defects that reduce electrical characteristics of devices. To generate the real device interface structure with the computer simulation, it is important to construct the a-SiO$$_{2}$$ structure on SiC. The slab model using 444 atoms for a-SiO$$_{2}$$ on a 4H-SiC (0001) crystal layer was constructed by using first-principles MD simulation. The heating and rapid quenching method was carried out to make an a-SiO$$_{2}$$/SiC interface structure. The heating temperature, the heating time and the speed of rapid quenching is 4000 K, 3.0 ps and -1000 K/ps, respectively. The interatomic distance and the bond angles of SiO$$_{2}$$ layers agreed well with the most probable values in bulk a-SiO$$_{2}$$, and there were no coordination defects in the neighborhood of the SiC substrate.

Journal Articles

Dynamical simulation of SiO$$_{2}$$/4H-SiC(0001) interface oxidation process; From first-principles

Onuma, Toshiharu*; Miyashita, Atsumi; Iwasawa, Misako*; Yoshikawa, Masahito; Tsuchida, Hidekazu*

Materials Science Forum, 556-557, p.615 - 620, 2007/00

We performed the dynamical simulation of the SiO$$_{2}$$/4H-SiC(0001) interface oxidation process using first-principles molecular dynamics based on plane waves and the slab model supercells method. The heat-and-cool method is used to prepare the initial interface structure. In this structure, there is no transition oxide layer or dangling bond at the SiO$$_{2}$$/SiC interface. As the trigger of the oxidation process, the carbon vacancy is introduced in the SiC layer near the interface. The oxygen molecules are added one by one to the empty sphere in the SiO$$_{2}$$ layer near the interface in the oxidation process simulation. The molecular dynamics simulation is carried out at 2500 K. The oxygen molecule is dissociated and forms bonds with the Si atom in the SiO$$_{2}$$ layer. The atoms of Si in the SiC layer at the SiO$$_{2}$$/4H-SiC(0001) interface are oxidized. Carbon clusters are formed in the interface layer. Oxygen molecules react with the carbon clusters and formed CO molecules.

Journal Articles

Defect layer in SiO$$_2$$-SiC interface proved by a slow positron beam

Maekawa, Masaki; Kawasuso, Atsuo; Yoshikawa, Masahito; Miyashita, Atsumi; Suzuki, Ryoichi*; Odaira, Toshiyuki*

Physica B; Condensed Matter, 376-377, p.354 - 357, 2006/04

 Times Cited Count:2 Percentile:86.49(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Structure of SiO$$_2$$/4H-SiC interface probed by positron annihilation spectroscopy

Maekawa, Masaki; Kawasuso, Atsuo; Yoshikawa, Masahito; Miyashita, Atsumi; Suzuki, Ryoichi*; Odaira, Toshiyuki*

Physical Review B, 73(1), p.014111_1 - 014111_9, 2006/01

 Times Cited Count:19 Percentile:34.56(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

First-principles molecular dynamics simulation of SiC devices; Generation of amorphous SiO$$_{2}$$/SiC interface

Miyashita, Atsumi; Yoshikawa, Masahito; Kano, Takuma; Onuma, Toshiharu*; Sakai, Takayuki*; Iwasawa, Misako*; Soneda, Naoki*

Annual Report of the Earth Simulator Center April 2004 - March 2005, p.287 - 291, 2005/12

Silicon carbide semiconductor device is expected to be used under a severe environment like the nuclear reactor and the space environment. On the semiconductor device interface, the electric charge state of the defect decides an electric characteristic. To emulate interfacial structure the $$rm SiO_{2}/SiC$$ interface structure is generated and the electronic geometry is decided by the first-principle molecular dynamics simulation with the earth simulator. The amorphous $$rm SiO_{2}/SiC$$ interface structure is made by medium-scale model of about 400 atoms. The heating temperature is 4000K, the heating time is 3.0ps, the speed of rapid cooling is -1000K/ps, and SiC movable layers in the interface are assumed to be 4 layers. In temperature 2200K the $$rm SiO_{2}$$ terminal was opened to make the $$rm SiO_{2}$$ layer more amorphous. The model has almost abrupt interface, however, some defects energy levels were still observed in the band gap. The energy levels are originated from interfacial oxygen. The localized electronic distribution of the dangling bond causes defect energy levels.

Journal Articles

Calculation of spatial distribution of dose rate for air under 300keV electron beam irradiation using a Monte Carlo code (EGS4-SPG code)

Hakoda, Teruyuki; Hanaya, Hiroaki; Kaneko, Hirohisa; Miyashita, Atsumi; Kojima, Takuji

Radioisotopes, 54(6), p.161 - 168, 2005/06

no abstracts in English

Journal Articles

Sulfur-doping of rutile-titanium dioxide by ion implantation; Photocurrent spectroscopy and first-principles band calculation studies

Umebayashi, Tsutomu; Yamaki, Tetsuya; Yamamoto, Shunya; Miyashita, Atsumi; Tanaka, Shigeru; Sumita, Taishi*; Asai, Keisuke*

Journal of Applied Physics, 93(9), p.5156 - 5160, 2003/05

 Times Cited Count:284 Percentile:1.26(Physics, Applied)

Sulfur (S)-doped titanium dioxide (TiO$$_{2}$$) was synthesized by ion implantation and subsequent thermal annealing. Compared to the pure TiO$$_{2}$$, a photocurrent was observed in the lower energy regions for the S-doped TiO$$_{2}$$. Based on the theoretical analyses by the first principles band calculations using the full potential linearized augmented plane wave methods within the generalized gradient approximation, the mixing of the S 3p states with the valence band (VB) was found to contribute to the increasing width of the VB. This leads to the bandgap narrowing in the S-doped TiO$$_{2}$$. Therefore, the photon-to-carrier conversion was induced during irradiation by visible light above 420 nm ($$<$$ 2.9 eV).

Journal Articles

Photo-induced surface charge separation in Cr-implanted TiO$$_2$$ thin film

Sumita, Taishi*; Yamaki, Tetsuya; Yamamoto, Shunya; Miyashita, Atsumi

Thin Solid Films, 416(1-2), p.80 - 84, 2002/09

 Times Cited Count:22 Percentile:31.31(Materials Science, Multidisciplinary)

Surface charge separation efficiencies of uniformly Cr-distributed rutile grown by pulse laser deposition(PLD) using Cr/TiO$$_2$$ multi-targets and rutile with Cr concentration gradient produced by ion implantation with the appropriate post-annealing process were characterized by photo-induced transient charge separation (PITCS) measurement. Cr depth profiles were obtained by secondary ion mass spectrometry(SIMS) and X-ray photoelectron spectroscopy(XPS) was used to determine that both surface Cr concentrations were the same. PITCS can be measured without direct contacts and without an externally applied field, and demonstrate the inherent property of charge separation without disturbing spontaneously formed surface band bending. There was a large charge separation for implanted rutile with Cr gradient, even in the visible light region ($$sim$$520nm), which was more remarkable than that of uniform rutile and epitaxial anatase films.

Journal Articles

Preparation of anatase and rutile thin films by controlling oxygen partial pressure

Syarif, D. G.; Miyashita, Atsumi; Yamaki, Tetsuya; Sumita, Taishi*; Choi, Y.; Ito, Hisayoshi

Applied Surface Science, 193(1-4), p.287 - 292, 2002/06

 Times Cited Count:83 Percentile:6.49(Chemistry, Physical)

Titanium dioxide ($$rm TiO_2$$) films on glass substrates were prepared by pulsed laser deposition (PLD) technique. The dependence of crystal structure, morphology and photocatalytic activity on oxygen partial pressure were investigated using X-ray diffraction (XRD), Atomic force microscope (AFM) and UV-VIS Spectrophotometer. By increasing oxygen partial pressure, the surface morphology changed from smooth to rough, and the crystal structure changed from rutile to anatase at fixed substrate temperature of 773 K. The change of the surface morphology and the formation of anatase structure by variation of oxygen partial pressure resulted in an increase of photocatalytic activity.

Journal Articles

Characterization of epitaxial TiO$$_{2}$$ films prepared by pulsed laser deposition

Yamamoto, Shunya; Sumita, Taishi; Yamaki, Tetsuya; Miyashita, Atsumi; Naramoto, Hiroshi

Journal of Crystal Growth, 237-239(Part1), p.569 - 573, 2002/04

The epitaxial growth of TiO$$_{2}$$ films has attracted much interest from the viewpoints of basic science and applications. In the present study, it is shown that TiO$$_{2}$$ films with anatase or rutile structure can be grown by pulsed laser deposition(PLD) with an ArF excimer laser under the controlled O$$_{2}$$ atmosphere. The TiO$$_{2}$$ films were prepared on the LaAlO$$_{3}$$, LSAT SrTiO$$_{3}$$ and $$alpha$$-Al$$_{2}$$O$$_{3}$$ single crystal substrates. The epitaxial films were analyzed by RBS and X-ray diffraction for investigating the crystallographic relationships with the substrates. The high quality anatase TiO$$_{2}$$(001) films have been successfully grown on the LaAlO$$_{3}$$ (001), LSAT (001) and SrTiO$$_{3}$$ (001) substrates at temperatures above 500$$^{circ}$$C. Also the high quality rutile TiO$$_{2}$$(100) and (001) films were obtained on the $$alpha$$-Al$$_{2}$$O$$_{3}$$ (0001) and (10-10), respectively.The optical properties were characterized by optical absorption measurements. The optical band gaps for anatase and rutile TiO$$_{2}$$ epitaxial films were evaluated to be 3.22 eV and 3.11 eV, respectively.

Journal Articles

Preparation of epitaxial TiO$$_{2}$$ films by PLD for photocatalyst applications

Yamaki, Tetsuya; Sumita, Taishi; Yamamoto, Shunya; Miyashita, Atsumi

Journal of Crystal Growth, 237-239(Part1), p.574 - 579, 2002/04

Pulsed laser deposition (PLD) with a KrF excimer laser was used to prepare epitaxial TiO$$_{2}$$ films on a (0001) sapphire substrate. The crystalline structure and surface morphology of the films were then investigated as a function of the laser power density in the PLD. X-ray diffraction and Raman spectroscopy results showed that the films were composed of the (100) oriented rutile phase with a small amount of the (001) oriented anatase. The anatase-to-rutile ratio in such phase-mixed films was controlled by the laser power; the ratio increased as the power density decreased. From atomic force microscopy observations, the film deposited at the lowest power was found to have a rough surface consisting of coarse grains. This film exhibited the best photocatalytic performance during the decomposition of the organic dyes possibly due to the maximum relative content of anatase and the large surface area.

Journal Articles

Preparation of epitaxial TiO$$_{2}$$ films by pulsed laser deposition technique

Yamamoto, Shunya; Sumita, Taishi; Sugiharuto; Miyashita, Atsumi; Naramoto, Hiroshi

Thin Solid Films, 401(1-2), p.88 - 93, 2001/12

 Times Cited Count:122 Percentile:3.07(Materials Science, Multidisciplinary)

The epitaxial growth of high-quality TiO$$_{2}$$ films has attracted much interest from the viewpoints of basic science and applications. In this study, it is shown that TiO$$_{2}$$ films with anatase and rutile structure can be prepared by pulsed laser deposition (PLD) with a Nd-YAG laser under the controlled O$$_{2}$$ atmosphere. The TiO$$_{2}$$ films with 200 nm thickness were prepared on the SrTiO$$_{3}$$, LaAlO$$_{3}$$, LSAT and $$alpha$$-Al$$_{2}$$O$$_{3}$$ single crystal substrates. The epitaxial films were analyzed by Rutherford backscattering spectrometry (RBS) combined with channeling and X-ray diffraction for the crystallographic relationships with the substrates. The high quality anatase TiO$$_{2}$$ (001) films have been successfully prepared on the LaAlO$$_{3}$$ (001), LSAT (001) and SrTiO$$_{3}$$ (001) substrates about 500$$^{circ}$$C substrate temperature. Also the high quality rutile TiO$$_{2}$$ (100) and TiO$$_{2}$$ (001) films were obtained on the $$alpha$$-Al$$_{2}$$O$$_{3}$$ (0001) and (10$$bar{1}$$0), respectively.

Journal Articles

Formation mechanisms for carbon onions and nanocapsules in C$$^{+}$$-ion implanted copper

Abe, Hiroaki; Yamamoto, Shunya; Miyashita, Atsumi; Sickafus, K. E.*

Journal of Applied Physics, 90(7), p.3353 - 3358, 2001/10

 Times Cited Count:12 Percentile:49.73(Physics, Applied)

no abstracts in English

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