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Journal Articles

Swelling of radiation-cured polymer precursor powder for silicon carbide by pyrolysis

Takeyama, Akinori; Idesaki, Akira; Sugimoto, Masaki; Yoshikawa, Masahito

Journal of Asian Ceramic Societies (Internet), 3(4), p.402 - 406, 2015/12

Journal Articles

A Development of super radiation-hardened power electronics using silicon carbide semiconductors; Toward MGy-class radiation resistivity

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

Journal Articles

Effect of humidity and temperature on the radiation response of SiC MOSFETs

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

Journal Articles

In-situ monitoring of ion-beam luminescence of Si-O-C(-H) ceramics under proton-beam irradiation

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

Journal Articles

Development of the RAQM2 aerosol chemical transport model and predictions of the Northeast Asian aerosol mass, size, chemistry, and mixing type

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:73.35(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.

Journal Articles

Gas permeation property of SiC membrane using curing of polymer precursor film by electron beam irradiation in helium atmosphere

Takeyama, Akinori; Sugimoto, Masaki; Yoshikawa, Masahito

Materials Transactions, 52(6), p.1276 - 1280, 2011/06

 Times Cited Count:17 Percentile:61.60(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$$_{2}$$ permeance of 3.1$$times$$10$$^{-7}$$ mol/m$$^{2}$$/s/Pa and the selectivity of 51 at 523 K. The H$$_{2}$$ permeance of the membrane was increased proportional to the temperature by the activated diffusion of H$$_{2}$$. 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.

JAEA Reports

Photocatalytic activity of Sulfur-doped TiO$$_{2}$$ 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 (H$$_{2}$$S) following oxygen atmosphere, Sulfer-doped titanium dioxide (TiO$$_{2}$$) fiber was obtained. Crystal structure of the fiber was identified as anatase phase of TiO$$_{2}$$. 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$$_{2}$$. Under visible light illumination, the fiber degraded Trichroloethylen (TCE) and produced carbon dioxide (CO$$_{2}$$). This shows Sulfer-doped TiO$$_{2}$$ fiber has the photocatalytic activity under visible light illumination.

Journal Articles

Blister formation in rutile TiO$$_{2}$$(100) films by helium irradiation

Yamamoto, 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:49.64(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Characterization of sulfur-doped TiO$$_{2}$$ films by RBS/C

Yamamoto, 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:52.71(Instruments & Instrumentation)

no abstracts in English

Journal Articles

Blister formation in rutile TiO$$_{2}$$ (100) thin films by helium ion implantation

Yamamoto, 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

Journal Articles

Formation of Cu precipitates by ion implantation and thermal annealing for the growth of oxide nanorods

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.

Journal Articles

Growth of ZnO nanorods on Cu implanted substrates

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.

Oral presentation

Gas permeation property of silicon carbide membrane prepared using radiation curing of polymer precursor film

Takeyama, Akinori; Sugimoto, Masaki; Yoshikawa, Masahito

no journal, , 

There is growing interest in H$$_{2}$$ 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$$_{2}$$ 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$$_{2}$$ 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$$_{2}$$ molecules diffused through the membrane by molecular sieving mechanism.

Oral presentation

Swelling of radiation-cured polycarbosilane during pyrolysis

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.

Oral presentation

Influence of $$gamma$$-ray irradiation under high temperature and humidity circumstance on the electrical characteristics of SiC MOSFETs

Takeyama, Akinori; Matsuda, Takuma; Yokoseki, Takashi; Mitomo, Satoshi; Murata, Koichi; Makino, Takahiro; Onoda, Shinobu; Okubo, Shuichi*; Tanaka, Yuki*; Kandori, Mikio*; et al.

no journal, , 

no abstracts in English

Oral presentation

Effect of high temperature and humidity on dose dependence of charges generated in SiC MOSFETs due to $$gamma$$-ray irradiation

Takeyama, Akinori; Matsuda, Takuma*; Yokoseki, Takashi*; Mitomo, Satoshi*; Murata, Koichi*; Makino, Takahiro; Onoda, Shinobu; Okubo, Shuichi*; Tanaka, Yuki*; Kandori, Mikio*; et al.

no journal, , 

Effect of $$gamma$$-ray irradiation under high temperature and humidity circumstances on the electrical characteristics of Silicon Carbide (SiC) Metal-Oxide-Semiconductor Field Effect Transistors (MOSFETs) was investigated. In the case of irradiation under high humidity circumstance, trapped oxide and interface charges densities generated due to irradiation were smaller than those for irradiation in dry circumstance. It is concluded that humidity circumstance suppressed the degradation of the electrical properties due to irradiation including threshold voltage shift and leakage current.

Oral presentation

Stability of silicon carbide membrane prepared from polymer precursor in steam

Takeyama, Akinori; Sugimoto, Masaki; Yoshikawa, Masahito

no journal, , 

Precursor-derived silicon carbide (SiC) membrane has been a promising candidate as a membrane for hydrogen separation in harsh condition. In this report, SiC membrane was exposed to steam and its gas permeances were measured. Polymer precursor, polycarbosilane (PCS) film was coated on a porous support.Subsequently, it was cured and cross-linked by an electron beam irradiation in helium atmosphere followed by the pyrolysis at 973 K or 1073 K. A series of preparation procedure was repeated three times to layer SiC film. Prepared membrane was exposed to steam at 773 K for 10 hours. Water vapor pressure was about 47 kPa. H$$_{2}$$ permeance of as-prepared membrane prepared via pyrolysis at 1073 K followed Arrhenius plot against the reciprocal temperature. This meanes H$$_{2}$$ permeated through the membrane by molecular sieving mechanism. H$$_{2}$$ permeance still followed Arrhenius plot after the exposure to steam. H$$_{2}$$ permeance of as-prepared membrane prepared via pyrolysis at 973 K also followed Arrhenius plot. However, the membrane was subject to oxidation by steam, consequently large sized pores for Knudsen diffufion of H$$_{2}$$ were formed in the membrane after the exposure.

Oral presentation

Electrical properties of SiC MOSFETs irradiated with $$gamma$$-rays at elevated temperature

Matsuda, 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 $$gamma$$-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.

Oral presentation

Single photon source in silicon carbide annealed at high temperature

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

Oral presentation

Tolerance of spin-Seebeck thermoelectricity against gamma ray irradiation

Okayasu, Satoru; Takeyama, Akinori*; Oshima, Takeshi*; Harii, Kazuya*; Ieda, Junichi; Ishida, Masahiko*; Saito, Eiji

no journal, , 

We are investigating the applications of spintronics devices in atomic fields. We reported the Tolerance of spin-Seebeck thermoelectricity against heavy swift ion irradiation previously. The tolerance of spin-Seebeck thermoelectricity against gamma ray irradiation will be reported at this conference. The spin thermoelectric properties after gamma ray irradiation up to $$sim$$1MGy at room temperature and at 150$$^{circ}$$C will be reported.

32 (Records 1-20 displayed on this page)