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Journal Articles

Doppler broadening of annihilation radiation of some single-element materials from the second to the sixth periods

Kawasuso, Atsuo; Maekawa, Masaki; Betsuyaku, Kiyoshi*

Journal of Physics; Conference Series, 225, p.012027_1 - 012027_5, 2010/06

 Times Cited Count:5 Percentile:87.1

Electron-positron momentum distribution obtained through the Doppler broadening of annihilation radiation measurement is very useful for identifying defects in materials. For the detailed analysis of Doppler broadening spectrum, precise theoretical calculation is needed. It is pointed out that the pseudo-potential method has a problem in the calculation of electron wavefunction near core region. To avoid this difficulty, some all-electron manner should be employed. We thus calculated the Doppler broadening spectra based on the electronic state calculation by the projector-augmented wave method and compared them with experimental spectra.

Journal Articles

Vacancy defects in electron-irradiated ZnO studied by Doppler broadening of annihilation radiation

Chen, Z. Q.*; Betsuyaku, Kiyoshi*; Kawasuso, Atsuo

Physical Review B, 77(11), p.113204_1 - 113204_4, 2008/03

 Times Cited Count:27 Percentile:73.2(Materials Science, Multidisciplinary)

Vacancy defects in ZnO induced by electron irradiation were characterized by the Doppler broadening of annihilation radiation measurements together with the local density approximation calculations. Zinc vacancies ($$V_{rm Zn}$$) are responsible for positron trapping in the as-irradiated state. These are annealed out below 200$$^{circ}$$C. The further annealing at 400$$^{circ}$$C results in the formation of secondary defects attributed to the complexes composed of zinc vacancies and zinc antisites ($$V_{rm Zn}$$-Zn$$_{rm O}$$).

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

Change of the Fermi surface across the critical pressure in CeIn$$_3$$; The de Haas-van Alphen study under pressure

Settai, Rikio*; Kubo, Tetsuo*; Shiromoto, Tomoyuki*; Honda, Daisuke*; Shishido, Hiroaki*; Sugiyama, Kiyohiro*; Haga, Yoshinori; Matsuda, Tatsuma; Betsuyaku, Kiyoshi*; Harima, Hisatomo*; et al.

Journal of the Physical Society of Japan, 74(11), p.3016 - 3026, 2005/11

 Times Cited Count:50 Percentile:12.02(Physics, Multidisciplinary)

We have studied a change of the Fermi surface in an antiferromagnet CeIn$$_3$$ via the de Haas-van Alphen experiment under pressure up to 3 GPa. With increasing pressure P, the Neel temperature $$T_N$$=10 K decreases and becomes zero at a critical pressure Pc $$simeq$$2.6 GPa. In the pressure region $$P > P_c$$, we have observed a large main Fermi surface named a, which indicates that the electronic state of 4 f electron in CeIn$$_3$$ changes from localized to itinerant at Pc, as observed in the similar antiferromagnets CeRh$$_2$$Si$$_2$$ and CeRhIn$$_5$$. The cyclotron effective mass $$m_c^*$$ of this main Fermi surface is extremely enhanced around Pc: $$m_c^*$$ $$simeq$$60 $$m_0$$ at 2.7 GPa for the magnetic field along the $$<$$100$$>$$ direction.

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.

Oral presentation

Identification of electron-induced defects in ZnO

Kawasuso, Atsuo; Chen, Z. Q.*; Maekawa, Masaki; Betsuyaku, Kiyoshi*

no journal, , 

no abstracts in English

Oral presentation

Doppler broadening spectra from transition metals; Comparison between experiment and calculation

Kawasuso, Atsuo; Maekawa, Masaki; Betsuyaku, Kiyoshi*

no journal, , 

no abstracts in English

7 (Records 1-7 displayed on this page)
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