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Takeyama, Akinori; Idesaki, Akira; Sugimoto, Masaki; Yoshikawa, Masahito
Journal of Asian Ceramic Societies (Internet), 3(4), p.402 - 406, 2015/12
Takeyama, Akinori; Matsuda, Takuma; Yokoseki, Takashi; Mitomo, Satoshi; Murata, Koichi; Makino, Takahiro; Onoda, Shinobu; Tanaka, Yuki*; Kandori, Mikio*; Yoshie, Toru*; et al.
Proceedings of 11th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-11) (Internet), p.134 - 137, 2015/11
Hijikata, Yasuto*; Mitomo, Satoshi*; Matsuda, Takuma*; Murata, Koichi*; Yokoseki, Takashi*; Makino, Takahiro; Takeyama, Akinori; Onoda, Shinobu; Okubo, Shuichi*; Tanaka, Yuki*; et al.
Proceedings of 11th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-11) (Internet), p.130 - 133, 2015/11
Narisawa, Masaki*; Koka, Masashi; Takeyama, Akinori; Sugimoto, Masaki; Idesaki, Akira; Sato, Takahiro; Hokazono, Hiroki*; Kawai, Taketoshi*; Iwase, Akihiro*
Journal of the Ceramic Society of Japan, 123(9), p.805 - 808, 2015/09
Kajino, Mizuo*; Inomata, Yayoi*; Sato, Keiichi*; Ueda, Hiromasa*; Han, Z.*; An, J.*; Katata, Genki; Deushi, Makoto*; Maki, Takashi*; Oshima, Naga*; et al.
Atmospheric Chemistry and Physics, 12(24), p.11833 - 11856, 2012/12
Times Cited Count：47 Percentile：72.67(Environmental Sciences)A new aerosol chemical transport model, Regional Air Quality Model 2 (RAQM2), was developed to simulate Asian air quality. We implemented a simple version of a modal-moment aerosol dynamics model and achieved completely dynamic solution of a gas-to-particle mass transfer over a wide range of aerosol diameters from 1 nm to super micro m. To consider a variety of atmospheric aerosol properties, a category approach is utilized: aerosols are distributed into 4 categories, Aitken, accumulation, soot aggregates, and coarse mode. A regional-scale simulation was performed for the entire year of 2006, covering Northeast Asian region. Statistical analysis showed the model reproduced the regional-scale transport and transformation of the major inorganic anthropogenic and natural air constituents within factors of 2 to 5. Modeled size distributions of total weight and chemical components were consistent with the observations, indicating simulations of aerosol mixing types were successful.
Takeyama, Akinori; Sugimoto, Masaki; Yoshikawa, Masahito
Materials Transactions, 52(6), p.1276 - 1280, 2011/06
Times Cited Count：17 Percentile：61.03(Materials Science, Multidisciplinary)SiC membranes were prepared using curing of precursor polymer (polycarbosilane, PCS) film by electron beam irradiation in helium atmosphere. The membrane prepared via curing of PCS film coated using 10 mass % PCS solution for dip-coating followed by immersing it for 30 s in PCS solution, showed H
permeance of 3.1
10
mol/m
/s/Pa and the selectivity of 51 at 523 K. The H permeance of the membrane was increased proportional to the temperature by the activated diffusion of H. It indicates SiC film without pinholes or cracks formed on the support. As the pyrolysis temperature of cured PCS film was increased, the selectivity of the membrane reached the maximum at 923 K.
fiber under visible light illumination (Joint research)Takeyama, Akinori; Yamamoto, Shunya; Yoshikawa, Masahito; Hasegawa, Yoshio*; Awatsu, Satoshi*
JAEA-Research 2007-012, 29 Pages, 2007/03
JAEA-Research-2007-012.pdf:3.77MB
The Sol-Gel derived precursor fiber was annealed under hydrogen disulfeid (HS) following oxygen atmosphere, Sulfer-doped titanium dioxide (TiO) fiber was obtained. Crystal structure of the fiber was identified as anatase phase of TiO. The energy band gap of the fiber was narrower by about 0.06 eV than that of anatase, which showed that it could absorb visible light. The fiber contains about 0.58 atomic % of Sulfer, and they located at the oxygen lattice site of TiO. Under visible light illumination, the fiber degraded Trichroloethylen (TCE) and produced carbon dioxide (CO). This shows Sulfer-doped TiO fiber has the photocatalytic activity under visible light illumination.
(100) films by helium irradiationYamamoto, Shunya; Nagata, Shinji*; Takeyama, Akinori; Yoshikawa, Masahito
Nuclear Instruments and Methods in Physics Research B, 249(1-2), p.374 - 376, 2006/08
Times Cited Count：8 Percentile：49.42(Instruments & Instrumentation)no abstracts in English
films by RBS/CYamamoto, Shunya; Takeyama, Akinori; Yoshikawa, Masahito
Nuclear Instruments and Methods in Physics Research B, 242(1-2), p.377 - 379, 2006/01
Times Cited Count：9 Percentile：52.40(Instruments & Instrumentation)no abstracts in English
(100) thin films by helium ion implantationYamamoto, Shunya; Nagata, Shinji*; Takeyama, Akinori; Yoshikawa, Masahito
Transactions of the Materials Research Society of Japan, 30(3), p.789 - 792, 2005/09
no abstracts in English
Takeyama, Akinori; Yamamoto, Shunya; Ito, Hiroshi; Yoshikawa, Masahito
Nuclear Instruments and Methods in Physics Research B, 232(1-4), p.333 - 337, 2005/05
Times Cited Count：0 Percentile：0.00(Instruments & Instrumentation)Cu precipitates were formed on Si(100) by 200 keV Cu ion implantation and subsequent annealing at 773 K. The shape of the Cu precipitates evolved from a large rectangle to a small elongated pyramid with increasing annealing time. This shape evolution seemed to result from the epitaxial formation of Cu precipitates to minimize the interfacial energy between the precipitate and the Cu implanted substrate. The average density of Cu precipitates monotonously increased and the average diameter of Cu precipitates decreased with increasing annealing time up to 1 h. These indicate that the morphology, size and average density of Cu precipitates can be controlled by varying annealing time, and that Cu ion implantation and subsequent annealing were effective in producing a substrate dispersed with catalytic particles for oxide nanorods growth.
Takeyama, Akinori; Yamamoto, Shunya; Yoshikawa, Masahito; Ito, Hiroshi
Japanese Journal of Applied Physics, Part 1, 44(1B), p.750 - 753, 2005/01
Times Cited Count：0 Percentile：0.00(Physics, Applied)Pyramid shaped Cu precipitates were formed on Si (100) surface as a result of 200 keV Cu ion implantation and subsequent annealing. Then, ZnO nanorods were successfully synthesized on the Cu implanted substrates by chemical vapor transport (CVT). Hexagonal shaped nanorods with a diameter of 200 nm were grown nearly perpendicular to the Cu implanted substrate and their average density was increased as increasing that of Cu precipitates. The facts strongly indicate the Cu precipitates served as the catalytic particles for the growth of ZnO rods.
Takeyama, Akinori; Sugimoto, Masaki; Yoshikawa, Masahito
no journal, ,
The conversion of polymer precursor, polycarbosilane (PCS) into polymer derived silicon carbide (SiC) by pyrolysis is accompanied by evolution of decomposed gas and volume shrinkage/expansion of PCS. It has been known thermally cured PCS powder is monotonically shrank, however, electron-beam cured PCS powder is expanded at the pyrolysis temperature of around 723 K. We aimed at clarifying why volume of PCS film is expanded by characterizing pyrolyzed powders cured by those methods by measuring the weight change, density and nitrogen isotherm. From the curve of weight decrease during the pyrolysis, it was observed thermally cured PCS evolved larger amount of gases in the temperature range from 673 to 923 K. In the same temperature range, larger total volume of pores formed in pyrolyzed powders was observed for thermally cured PCS powder. It indicates PCS powders were swelled when decomposed gases were evolved. In particular, for electron-beam cured powders, it was observed increase of total pore volume at 723 K even though hardly gases were evolved and the conversion took place, which attributed volume expansion of the PCS powder without shrinkage usually accompanied by the conversion.
Takeyama, Akinori; Sugimoto, Masaki; Yoshikawa, Masahito
no journal, ,
There is growing interest in H production using inorganic membrane stable in reactant gases such as carbon monoxide (CO) or steam. In this study, we prepared an inorganic membrane from polymer-derived silicon carbide (SiC) using electron beam curing of polymer precursor film. Alpha almina tube, which is chemically stable but has sized pore (averaged diameter size 100 nm), was used as the support. First, supports were dipped in the 10 mass% polycarbosilne (PCS), polymer precursor solution for 1 s and drawn up (the first dipping). After drying, some of those supports coated with PCS film were immersed into another PCS solution whose concentration was 3 mass% for 0.8, 1.5 and 2 s (the second dipping). They were cured by electron beam irradiation in helium atmosphere and pylolyzed at 973 K in argon atmosphere. H permeance of SiC membrane prepared via only the first dipping increased with increasing the temperature, but not following the Arrhenius plot. This means sub-nano meter sized pores and a few of large defects coexisted in the membrane. Whereas, H permeance of the membrane prepared via the first and 1.5s of second dipping increased following the Arrhenius plot. Activation energy of 7.5 kJ/mol calculated from slope of the plot indicates that pores of the support were plugged by SiC film and thermally activated H molecules diffused through the membrane by molecular sieving mechanism.
Oshima, Takeshi; Lohrmann, A.*; Johnson, B. C.*; Castelletto, S.*; Onoda, Shinobu; Makino, Takahiro; Takeyama, Akinori; Klein, J. R.*; Bosi, M.*; Negri, M.*; et al.
no journal, ,
no abstracts in English
Takeyama, Akinori; Sugimoto, Masaki; Yoshikawa, Masahito
no journal, ,
Silicon carbide (SiC) films as a hydrogen separation membrane were prepared using a novel preparation technique. The films were obtained by a coating of precursor films on porous alumina supports followed by an immersion into cycohexane, curing in an inert atmosphere and pyrolisis. A selectivity of the film, which is defined as the ratio of the amount of hydrogen (H) to nitrogen (N) which passed thorough the membrane, was increased up to 6.1 as increasing the immersion time. This is supposed that precursor in pores is dissolved by cyclohexane and pores are filled with the precursor solution, which leads to a decrease of the pore diameter and an improvement of the selectivity.
Takeyama, Akinori; Yamamoto, Shunya; Ito, Hiroshi; Yoshikawa, Masahito
no journal, ,
no abstracts in English
Takeyama, Akinori; Sugimoto, Masaki; Yoshikawa, Masahito
no journal, ,
Hydrogen separation membrane consisted of Silicon Carbide(SiC) thin fim and a SiC intermediate layer was prepared. The intermediate layer was deposited on a porous alumina support by a pylorisis after a coating of the SiC precursor film, an immersion of the film in a solvent and a curing. Maximum hydrogen permeanse and selectivity of the membrane with the "immersed" intermediate layer at 523.15 K was larger than that of the membrane with "un-immersed" layer.
Takeyama, Akinori; Sugimoto, Masaki; Yoshikawa, Masahito
no journal, ,
Inorganic membrane prepared from thermally stable precursor-derived silicon carbide (SiC) has been paid attention for the use of hydrogen or carbon dioxide separation. For preventing formation of defects called as pinholes or cracks in the membrane, volume shrinkage of polymer precursor, polycarbosilane (PCS) should be as small as possible when PCS is converted into SiC. We aim at revealing mechanism for prevention of the volume shrinkage of PCS powder during pyrolysis. With increasing the pyrolysis temperature from 673 K to 823 K, density of pyrolyzed PCS powder was decreased, whilst calculated volume change was increased, indicating PCS powder swelled. Furthermore, increased amount of total pore volume compared with that of un-pyrolyzed powder was observed in the same temperature range. We found volume shrinkage of PCS powder was relieved by swelling.
-rays at elevated temperatureMatsuda, Takuma; Yokoseki, Takashi; Mitomo, Satoshi; Murata, Koichi; Makino, Takahiro; Takeyama, Akinori; Onoda, Shinobu; Okubo, Shuichi*; Tanaka, Yuki*; Kandori, Mikio*; et al.
no journal, ,
Silicon carbide (SiC) is expected to be applied to Metal-Oxide-Semiconductor (MOS) FETs used in harsh radiation environments to decommission TEPCO Fukushima Daiichi nuclear reactors. To develop radiation resistant SiC MOS FETs, clarification of their radiation response under elevated temperature is required. We measured capacitance-voltage (C-V) characteristics of SiC MOSFETs irradiated with -rays at 423 K in nitrogen atmosphere. The samples were vertical power 4H-SiC MOSFETs with the blocking voltage of 1200 V and the rated current of 20 A with the gate oxide thickness of 45 nm. Typical C-V curve of a SiC MOSFET irradiated even up to 5 kGy was shifted to negative voltage side, suggesting that the positive charges generated in gate oxide by irradiation. While, no significant change in the slope of the curve was observed, indicating that interface traps between the gate oxide and SiC were merely generated. The radiation response of SiC MOS FETs under elevated temperature predominantly depends on the amount of positive charges generated in the gate oxide.
