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Journal Articles

Positron study of electron irradiation-induced vacancy defects in SiC

Kawasuso, Atsuo; Yoshikawa, Masahito; Ito, Hisayoshi; Krause-Rehberg, R.*; Redmann, F.*; Higuchi, Takatoshi*; Betsuyaku, Kiyoshi*

Physica B; Condensed Matter, 376-377, p.350 - 353, 2006/04

 Times Cited Count:11 Percentile:48.8(Physics, Condensed Matter)

In this presentation, we report identification of vacancy defects in cubic and hexagonal SiC irradiated with fast electrons through electron-pisitron momentum distribution measurements and theoretical analyses. In cubic SiC isolated silicon vacancies are responsible for positron trapping. The lifetime of positrons trapped at silicon vacancies is prolonged due to the outward lattice relaxation. Because of the local tetrahedral symmetry of silicon vacancies, the observed momentum distributions are consistently explained. In the case of hexagonal SiC, one particular vacancy defects appearing after annealing of isolated silicon vacancies have dangling bonds along the c-axis. From the enhancement of positron annihilation probability with carbon 1s electrons, the above defects are attributed to carbon-vacancy-antisite-carbon complexes.

Journal Articles

Electron-positron momentum distributions associated with isolated silicon vacancies in 3C-SiC

Kawasuso, Atsuo; Yoshikawa, Masahito; Ito, Hisayoshi; Chiba, Toshinobu*; Higuchi, Takatoshi*; Betsuyaku, Kiyoshi*; Redmann, F.*; Krause-Rehberg, R.*

Physical Review B, 72(4), p.045204_1 - 045204_6, 2005/07

 Times Cited Count:15 Percentile:55.49(Materials Science, Multidisciplinary)

Two-dimensional angular correlation of annihilation radiation (2D-ACAR) and coincidence Doppler broadening (CDB) of annihilation radiation measurements have been performed on electron-irradiated n-type 3C SiC in which isolated silicon vacancies are responsible for positron trapping. After irradiation, the intensity of CDB spectrum increased and decreased in low and high momentum regions, respectively. These fetures were explained by the theoretical calculation considering silicon vacancies. The center region of 2D-ACAR spectra became isotropic after iradiation, while the overall anisotropies extending within the Jones zone were conserved suggesting that isolated silicon vacancies have the tetrahedral symmetry as expected from the previous electron spin resonance study.

Journal Articles

Angular correlation of annihilation radiation associated with vacancy defects in electron-irradiated 6$$H$$ SiC

Kawasuso, Atsuo; Chiba, Toshinobu*; Higuchi, Takatoshi*

Physical Review B, 71(19), p.193204_1 - 193204_4, 2005/05

 Times Cited Count:15 Percentile:55.49(Materials Science, Multidisciplinary)

Electron-positron momentum distributions associated with vacancy defects in 6H SiC after irradiation with 2 MeV electrons and annealing at 1000$$^{circ}C$$ have been studied using angular correlation of annihilation radiation (ACAR) measurements. It was confirmed that the above vacancy defects have dangling bonds along the c-axis and the rotational symmetry around it. The first principles calculation suggests that the vacancy defects are attributable to either carbon-vacancy-carbon-antisites complexes or silicon-vacancy-nitrogen pairs, while isolated carbon vacancies, silicon vacancies and nearest neighbor divacancies are ruled out.

Journal Articles

Relativistic effects on chaos; Loss mechanism of runaway electrons in a tokamak

Tokuda, Shinji; Higuchi, Takatoshi*; Suzuki, Noriyuki*

Purazuma, Kaku Yugo Gakkai-Shi, 77(12), p.1180 - 1220, 2001/12

no abstracts in English

Oral presentation

Provisional dose calculation to examine the radiation protection in geological disposal of high-level radioactive waste

Nakai, Kunihiro*; Kai, Michiaki*; Okoshi, Minoru; Kato, Tomoko; Yamaguchi, Tetsuji; Sasaki, Takayuki*; Hattori, Takatoshi*; Miyazaki, Shinichiro*; Yoshizawa, Yuji*; Higuchi, Natsuko*; et al.

no journal, , 

no abstracts in English

Oral presentation

The Evaluation of the radon dose of radioactivity in high-level radioactive waste geological disposal facility

Yoshizawa, Yuji*; Kai, Michiaki*; Okoshi, Minoru; Kato, Tomoko; Yamaguchi, Tetsuji; Sasaki, Takayuki*; Hattori, Takatoshi*; Miyazaki, Shinichiro*; Higuchi, Natsuko*; Tokonami, Shinji*; et al.

no journal, , 

no abstracts in English

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