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Nagao, Fumiya; Niizato, Tadafumi; Sasaki, Yoshito; Ito, Satomi; Watanabe, Takayoshi; Dohi, Terumi; Nakanishi, Takahiro; Sakuma, Kazuyuki; Hagiwara, Hiroki; Funaki, Hironori; et al.
JAEA-Research 2019-002, 235 Pages, 2019/08
JAEA-Research-2019-002.pdf:21.04MB
The accident of the Fukushima Daiichi Nuclear Power Station (hereinafter referred to 1F), Tokyo Electric Power Company Holdings, Inc. occurred due to the Great East Japan Earthquake, Sanriku offshore earthquake, of 9.0 magnitude and the accompanying tsunami. As a result, large amount of radioactive materials was released into the environment. Under these circumstances, JAEA has been conducting Long-term Environmental Dynamics Research concerning radioactive materials released in environment, especially migration behavior of radioactive cesium since November 2012. This report is a summary of the research results that have been obtained in environmental dynamics research conducted by JAEA in Fukushima Prefecture.
Abe, Tomohisa; Shimazaki, Takejiro; Osugi, Takeshi; Nakazawa, Osamu; Yamada, Naoto*; Yuri, Yosuke*; Sato, Takahiro*
QST-M-16; QST Takasaki Annual Report 2017, P. 140, 2019/03
no abstracts in English
/AlON stacked gate dielectrics for AlGaN/GaN MOS heterojunction field-effect transistorsWatanabe, Kenta*; Terashima, Daiki*; Nozaki, Mikito*; Yamada, Takahiro*; Nakazawa, Satoshi*; Ishida, Masahiro*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; et al.
Japanese Journal of Applied Physics, 57(6S3), p.06KA03_1 - 06KA03_6, 2018/06
Times Cited Count：4 Percentile：32.09(Physics, Applied)The advantage of SiO/AlON stacked gate dielectrics over SiO, AlON and AlO
single dielectric layers was demonstrated. Our systematic research revealed that the optimized stacked structure with 3.3-nm-thick AlON interlayer is beneficial in terms of superior interface quality, reduced gate leakage current and C-V hysteresis for next-generation high frequency and high power AlGaN/GaN MOS-HFETs.
Nozaki, Mikito*; Watanabe, Kenta*; Yamada, Takahiro*; Shih, H.-A.*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.
Japanese Journal of Applied Physics, 57(6S3), p.06KA02_1 - 06KA02_7, 2018/06
Times Cited Count：4 Percentile：32.09(Physics, Applied)We fabricated AlON dielectric films by repeating thin AlN deposition and in situ O oxidation for AlGaN/GaN MOS-HFETs. Uniform nitrogen distribution is achievable by the proposed ALD-based process and that nitrogen concentration can be precisely controlled by changing AlN thickness (ALD cycle number) in each step. It was found that AlON films grown by ALD system offers significant advantages in terms of practical application while keeping superior Vth stability and electrical properties at the insulator/AlGaN interface in AlGaN/GaN MOS-HFETs.
Abe, Tomohisa; Shimazaki, Takejiro; Osugi, Takeshi; Yamada, Naoto*; Yuri, Yosuke*; Sato, Takahiro*
QST-M-8; QST Takasaki Annual Report 2016, P. 61, 2018/03
no abstracts in English
Sakai, Takuro; Iikura, Hiroshi; Yamada, Naoto*; Sato, Takahiro*; Ishii, Yasuyuki*; Uchida, Masaya*
QST-M-8; QST Takasaki Annual Report 2016, P. 140, 2018/03
/GaN stacks for high-quality GaN-based metal-oxide-semiconductor devices with improved gate dielectric reliabilityYamada, Takahiro*; Watanabe, Kenta*; Nozaki, Mikito*; Yamada, Hisashi*; Takahashi, Tokio*; Shimizu, Mitsuaki*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; Watanabe, Heiji*
Applied Physics Express, 11(1), p.015701_1 - 015701_4, 2018/01
Times Cited Count：9 Percentile：12.47(Physics, Applied)A simple and feasible method for fabricating high-quality and highly reliable GaN-based metal-oxide-semiconductor (MOS) devices was developed on the basis of systematic physical and electrical characterizations. Chemical vapor deposition of SiO films directly onto GaN substrates forming Ga-oxide interlayers was used to fabricate SiO/GaO
/GaN stacked structures. Although well-behaved hysteresis-free GaN-MOS capacitors with extremely low interface state density below 10
cm
eV
were obtained by post-deposition annealing, Ga diffusion into overlying SiO layers severely degraded the insulating property and dielectric breakdown characteristics of the MOS devices. However, this problem was found to be solved by employing rapid thermal processing, leading to superior performance of the GaN-MOS devices in terms of interface quality, insulating property and gate dielectric reliability.
Watanabe, Kenta*; Nozaki, Mikito*; Yamada, Takahiro*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ishida, Masahiro*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.
Applied Physics Letters, 111(4), p.042102_1 - 042102_5, 2017/07
Times Cited Count：10 Percentile：22.28(Physics, Applied)AlGaN/GaN HFET (hetero-junction field-effect transitor) has gained much attention as next-generation high frequency and high power devices. In this study, we systematically investigated the interface reaction between Al-based dielectrics (AlO and AlON) and AlGaN layer during deposition and post-deposition annealing (PDA), and revealed high thermal stability of AlON/AlGaN interface.
Abe, Tomohisa; Shimazaki, Takejiro; Nakayama, Takuya; Osone, Osamu; Osugi, Takeshi; Nakazawa, Osamu; Yuri, Yosuke*; Yamada, Naoto*; Sato, Takahiro*
QST-M-2; QST Takasaki Annual Report 2015, P. 83, 2017/03
no abstracts in English
Yamada, Takahiro*; Ito, Joyo*; Asahara, Ryohei*; Watanabe, Kenta*; Nozaki, Mikito*; Nakazawa, Satoshi*; Anda, Yoshiharu*; Ishida, Masahiro*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; et al.
Journal of Applied Physics, 121(3), p.035303_1 - 035303_9, 2017/01
Times Cited Count：28 Percentile：5.61(Physics, Applied)Initial oxidation of GaN(0001) epilayers and subsequent growth of thermal oxides in dry oxygen ambient were investigated by means of X-ray photoelectron spectroscopy, spectroscopic ellipsometry, atomic force microscopy and X-ray diffraction measurements. It was found that, whereas initial oxide formation tends to saturate at temperatures below 800
C, selective growth of small oxide grains proceeds at dislocations in the epilayers, followed by noticeable grain growth leading to rough surface morphology at higher oxidation temperatures. This indicates that oxide growth and its morphology are crucially dependent on the defect density in the GaN epilayers. Structural characterizations also revealed that polycrystalline 
- and 
-phase GaO grains in an epitaxial relation with the GaN substrate are formed from the initial stage of the oxide growth. On the basis of these experimental findings, we also developed a comprehensive model for GaN oxidation mediated by nitrogen removal and mass transport.
Asahara, Ryohei*; Nozaki, Mikito*; Yamada, Takahiro*; Ito, Joyo*; Nakazawa, Satoshi*; Ishida, Masahiro*; Ueda, Tetsuzo*; Yoshigoe, Akitaka; Hosoi, Takuji*; Shimura, Takayoshi*; et al.
Applied Physics Express, 9(10), p.101002_1 - 101002_4, 2016/10
Times Cited Count：21 Percentile：15.16(Physics, Applied)The superior physical and electrical properties of AlON gate dielectrics on AlGaN/GaN substrates in terms of thermal stability, reliability, and interface quality were demonstrated by direct AlON deposition and subsequent annealing. Nitrogen incorporation into alumina was proven to be beneficial both for suppressing intermixing at the insulator/AlGaN interface and reducing the number of electrical defects in AlO films. Consequently, we achieved high-quality AlON/AlGaN/GaN metal-oxide-semiconductor capacitors with improved stability against charge injection and a reduced interface state density as low as 1.2
10
cmeV. The impact of nitrogen incorporation into the insulator was discussed on the basis of experimental findings.
Koka, Masashi; Ishii, Yasuyuki; Yamada, Naoto; Okubo, Takeru; Kada, Wataru*; Kitamura, Akane; Iwata, Yoshihiro*; Kamiya, Tomihiro; Sato, Takahiro
JAEA-Technology 2016-006, 41 Pages, 2016/03
JAEA-Technology-2016-006.pdf:14.03MB
A MeV-class light ion microbeam system has been developed for micro-analysis and micro-fabrication with high spatial resolution at 3-MV single-ended accelerator in Takasaki Ion Accelerators for Advanced Radiation Application of Takasaki Advanced Radiation Research Institute, Sector of Nuclear Science Research, Japan Atomic Energy Agency. This report describes the technical improvements for the main apparatus (the accelerator, beam-transport lines, and microbeam system), and auxiliary equipments/ parts for ion beam applications such as Particle Induced X-ray/Gamma-ray Emission (PIXE/PIGE) analysis, 3-D element distribution analysis using PIXE-Computed Tomography(CT), Ion Beam-Induced Luminescence (IBIL) analysis, and Proton Beam Writing with the microbeam scanning, with functional outline of these apparatus and equipments/parts.
Usui, Aya; Chiba, Atsuya; Yamada, Keisuke; Yokoyama, Akihito; Kitano, Toshihiko*; Takayama, Terumitsu*; Orimo, Takao*; Kanai, Shinji*; Aoki, Yuki*; Hashizume, Masashi*; et al.
Dai-28-Kai Tandemu Kasokuki Oyobi Sono Shuhen Gijutsu No Kenkyukai Hokokushu, p.117 - 119, 2015/12
no abstracts in English
Yuri, Yosuke; Yuyama, Takahiro; Ishizaka, Tomohisa; Koka, Masashi; Yamada, Naoto
Proceedings of 12th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.420 - 423, 2015/09
no abstracts in English
Yuyama, Takahiro; Ishibori, Ikuo; Kurashima, Satoshi; Yoshida, Kenichi; Ishizaka, Tomohisa; Chiba, Atsuya; Yamada, Keisuke; Yokoyama, Akihito; Usui, Aya; Miyawaki, Nobumasa; et al.
Proceedings of 12th Annual Meeting of Particle Accelerator Society of Japan (Internet), p.302 - 304, 2015/09
no abstracts in English
Usui, Aya; Uno, Sadanori; Chiba, Atsuya; Yamada, Keisuke; Yokoyama, Akihito; Kitano, Toshihiko*; Takayama, Terumitsu*; Orimo, Takao*; Kanai, Shinji*; Aoki, Yuki*; et al.
Dai-27-Kai Tandemu Kasokuki Oyobi Sono Shuhen Gijutsu No Kenkyukai Hokokushu, p.118 - 121, 2015/03
no abstracts in English
Yamada, Keisuke; Saito, Yuichi; Ishii, Yasuyuki; Matoba, Shiro; Chiba, Atsuya; Yokoyama, Akihito; Usui, Aya; Sato, Takahiro; Okubo, Takeru; Uno, Sadanori
JAEA-Review 2013-059, JAEA Takasaki Annual Report 2012, P. 159, 2014/03
no abstracts in English
Uno, Sadanori; Chiba, Atsuya; Yamada, Keisuke; Yokoyama, Akihito; Usui, Aya; Saito, Yuichi; Ishii, Yasuyuki; Sato, Takahiro; Okubo, Takeru; Nara, Takayuki; et al.
JAEA-Review 2013-059, JAEA Takasaki Annual Report 2012, P. 179, 2014/03
Three electrostatic accelerators at TIARA were operated on schedule in fiscal year 2012 except changing its schedule by cancellations of users. The yearly operation time of the 3 MV tandem accelerator, the 400 kV ion implanter and the 3MV single-ended accelerator were in the same levels as the ordinary one, whose operation time totaled to 2,073, 1,847 and 2,389 hours, respectively. The tandem accelerator had no trouble, whereas the ion implanter and the single-ended accelerator stopped by any troubles for one day and four days, respectively. The molecular ion beam of helium hydride was generated by the ion implanter, because the users required irradiation of several cluster ions in order to study the effect of irradiation. As a result, its intensity of beam was 50 nA at 200 kV. The ion beam of tungsten (W) at 15 MeV was accelerated by the tandem accelerator, whose intensity was 20 nA at charge state of 4+, because of the request from a researcher in the field of nuclear fusion.
Yamasaki, Seiko*; Zwingmann, H.*; Yamada, Kunimi*; Tagami, Takahiro*; Umeda, Koji
Chemical Geology, 351, p.168 - 174, 2013/08
Times Cited Count：19 Percentile：31.07(Geochemistry & Geophysics)Constraining of the timing of fault zone formation is of fundamental geotectonic importance to understand structural evolution and brittle fault processes. Here, we present authigenic illite K-Ar age data from brittle fault zones comprising two gouges within the Toki granite, central Japan. The gouge samples were collected from a shaft at the Mizunami Underground Research Laboratory, and were separated into five grain-size fractions. K-Ar ages of clay fractions decrease with grain size, suggesting enrichment in finer fraction of more-recently grown authigenic illites. The K-Ar ages of the fractions range from 53.6 to 42.7 Ma (Paleogene-Early to Middle Eocene). The 
0.1 
m fractions yield ages of 42.7 and 46.5 Ma. This age range is consistent with the stability field of illite and the main temperature field of brittle deformation within the cooling history of the Toki granite, supported by extensive thermochronological data of the host rock.
Uno, Sadanori; Chiba, Atsuya; Yamada, Keisuke; Yokoyama, Akihito; Usui, Aya; Kitano, Toshihiko*; Takayama, Terumitsu*; Orimo, Takao*; Kanai, Shinji*; Aoki, Yuki*; et al.
Dai-26-Kai Tandemu Kasokuki Oyobi Sono Shuhen Gijutsu No Kenkyukai Hokokushu, p.79 - 81, 2013/07
Three electrostatic accelerators at TIARA were operated on schedule in fiscal year 2012 except changing its schedule by cancellations of users. The yearly operation time of the 3MV tandem accelerator, the 400 kV ion implanter and the 3 MV single-ended accelerator were in the same levels as the ordinary one, whose operation time totaled to 2,073, 1,847 and 2,389 hours, respectively. The tandem accelerator had no trouble, whereas the ion implanter and the single-ended accelerator stopped by any troubles for one day and four days, respectively. The ion implanter generated molecular ion beam of helium hydride by using the Freeman type ion source, because of the request from the user. As a result, its intensity of beam was 50 nA at 200 kV.
