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Fujita, Hiroe*; Yuyama, Kenta*; Li, X.*; Hatano, Yuji*; Toyama, Takeshi*; Ota, Masayuki; Ochiai, Kentaro; Yoshida, Naoaki*; Chikada, Takumi*; Oya, Yasuhisa*
Physica Scripta, 2016(T167), p.014068_1 - 014068_5, 2016/02
Times Cited Count：33 Percentile：82.89(Physics, Multidisciplinary)The irradiation defects were introduced by Fe
irradiation, fission neutron irradiation and D-T neutron irradiation. After the irradiation, the deuterium ions (D
) implantation was performed and the D retention behavior was evaluated by thermal desorption spectroscopy. The experimental results indicated that dense vacancies and voids within the shallow region near the surface were introduced by Fe irradiation. The trapping state of D by vacancies and void were clearly controlled by the damage concentration and the voids would become the most stable D trapping site. For fission neutron irradiated W, most of the D was adsorbed on the surface and/or trapped by dislocation loops and no vacancies and voids for D trapping due to its lower damage concentration. D trapping by vacancies were found in the bulk of D-T neutron irradiated W, indicating that the neutron energy distribution could make a large impact on irradiation defect formation and the D retention behavior.
O
thin films on Si (100) by ion beam sputter depositionMao, W.*; Fujita, Masaya*; Chikada, Takumi*; Yamaguchi, Kenji; Suzuki, Akihiro*; Terai, Takayuki*; Matsuzaki, Hiroyuki*
Surface & Coatings Technology, 283, p.241 - 246, 2015/12
Times Cited Count：3 Percentile：13.89(Materials Science, Coatings & Films)Single-phase nanocrystalline thin films of ErO (440) has been first prepared using Si (100) substrates by ion beam sputter deposition at 973 K at a pressure of 
10
Pa and 
-
annealing at 1023 K at a pressure of 
10
Pa. Er silicides formed during the deposition are eliminated via the annealing, which results in the single phase and the smooth surface of the ErO thin films. The epitaxial relationship between Si (100) and ErO (110) is clarified by X-ray diffraction and reflection high energy electron diffraction.
Usui, Takahiro*; Sawada, Akihiko; Amaya, Masaki; Suzuki, Akihiro*; Chikada, Takumi*; Terai, Takayuki*
Journal of Nuclear Science and Technology, 52(10), p.1318 - 1322, 2015/10
Times Cited Count：48 Percentile：97.39(Nuclear Science & Technology)SiC coating is one of countermeasures for the prevention of oxidation and hydrogen embrittlement of fuel claddings because SiC has high resistance of oxidation and hydrogen permeation. Hydrogen permeation and oxidation experiments for the cladding materials with SiC coatings were conducted in unirradiated conditions. The sputtering method was employed to make SiC coatings. In the hydrogen permeation experiment, SUS316 was used as a base material of the coating. SUS316 with SiC coatings showed hydrogen permeation reduction by one order of magnitude. In the oxidation experiments, Zry-4 and SUS316 were used as base materials of the coatings. The weight gain of the Zry-4 specimens with a SiC coating decreased by about one-fifth compared to the uncoated ones. This phenomenon was observed for SUS316 at 750 
C as well. The peel-off of the coating was observed in some experiments, and it is considered that the peel-off was caused by the difference of the thermal expansions between coatings and base materials. Thicker coatings showed better oxidation resistance, but thinner coatings showed more tolerance of peel-off.
O (001) surface; A DFT studyMao, W.*; Chikada, Takumi*; Shimura, Kenichiro*; Suzuki, Akihiro*; Yamaguchi, Kenji; Terai, Takayuki*
Journal of Nuclear Materials, 443(1-3), p.555 - 561, 2013/11
Times Cited Count：3 Percentile：25.73(Materials Science, Multidisciplinary)In this work, 
calculations based on density functional theory (DFT) and generalized gradient approximation were performed to investigate the structural and electronic properties of the cubic Er
O
(001) surface and H adsorption processes on this surface. Several stable adsorption sites were identified, and at the most energetically favorable adsorption sites it was found that H bonds with O atoms at the cubic ErO (001) surface with an adsorption energy of 295.68 kJ mol
at coverage 1/8 ML, which was inclined to decrease with the increase of H coverage (
1/4 ML). In addition, the calculations revealed that the dissociative H atom configurations have adsorption energies that are at least 152.64 kJ mol greater than the H molecule configurations on the surface. These results are discussed in regard of the hydrogen isotope permeation behavior in the tritium permeation barrier in a fusion reactor.
Mao, W.*; Chikada, Takumi*; Suzuki, Akihiro*; Terai, Takayuki*; Yamaguchi, Kenji
Journal of Plasma and Fusion Research SERIES, Vol.10, p.27 - 32, 2013/02
A tritium permeation barrier (TPB) is strongly required in fusion blankets for the reduction of loss of fuel and radiological hazard. However, the precise tritium permeation mechanism through the TPB coatings has not been clarified yet, because of their complicated crystal structures. To understand the microscopic mechanism, we have not only prepared and characterized nanostructured ceramic ErO thin films, but also studied the energetics and mobility of hydrogen atom in cubic bulk ErO using ab initio density-functional calculations. The estimated diffusion activation energy (
) of interstitial H is somewhat higher than the diffusion energy barrier observed experimentally at 873 K. It is then considered that diffusion and permeation of hydrogen and its isotopes through the ErO coatings are likely to be dominated by the grain boundary rather than by the grain.
Mao, W.*; Chikada, Takumi*; Suzuki, Akihiro*; Terai, Takayuki*; Yamaguchi, Kenji
no journal, ,
O thin films by ion beam sputter deposition methodFujita, Masaya*; Yamaguchi, Kenji; Asaoka, Hidehito; Mao, W.*; Chikada, Takumi*; Suzuki, Akihiro*; Terai, Takayuki*
no journal, ,
no abstracts in English
Usui, Takahiro*; Sawada, Akihiko; Amaya, Masaki; Suzuki, Akihiro*; Chikada, Takumi*; Terai, Takayuki*
no journal, ,
SiC coatings were fabricated on SUS316 and Zircaloy-4 substrate. Hydrogen permeation experiment and oxidation experiment were performed. From hydrogen permeation experiment to SiC coated specimen on SUS316 subsrate, permeability of specimen was smaller in one order in magnitude than that of uncoated. From oxidation experiment on Zircaloy-4 substrate, weight gain and thickness of oxide film decreased. Specimens with thicker coating has less weight gain than that with thinner coating, however, thicker coating was peeled off more than thinner coating after oxidized in 1200C.
O film by means of ion beam sputter depositionFujita, Masaya*; Yamaguchi, Kenji; Asaoka, Hidehito; Mao, W.*; Chikada, Takumi*; Suzuki, Akihiro*; Terai, Takayuki*
no journal, ,
no abstracts in English
Fujita, Hiroe*; Yuyama, Kenta*; Uemura, Yuki*; Sakurada, Shodai*; Hu, C.*; Chikada, Takumi*; Oya, Yasuhisa*; Ota, Masayuki; Ochiai, Kentaro
no journal, ,
Tungsten (W) is the candidate for the plasma facing material in D-T fusion reactors. The distribution of defects introduced by neutron irradiation is formed uniformly throughout the bulk, while that by heavy-ion irradiation is concentrated in the shallow region near the surface. Therefore, it is expected that the hydrogen isotope behaviour in neutron irradiated W would be different from that in heavy-ion irradiated W. In this study, the irradiation defects were introduced by Fe irradiation, fission neutron irradiation and 14 MeV neutron irradiation from D-T fusion reaction. After the irradiation, the deuterium ions (D) implantation was performed and the D retention behaviour was evaluated by thermal desorption spectroscopy (TDS). The experimental results indicate that stable trapping sites would be formed into W by 14 MeV neutron irradiation with lower neutron fluence, on the other hand, only low energy trapping sites will be formed by fission neutron irradiation.
