Numerical interpretation of hydrogen thermal desorption spectra for iron with hydrogen-enhanced strain-induced vacancies

Ebihara, Kenichi; Sugiyama, Yuri*; Matsumoto, Ryosuke*; Takai, Kenichi*; Suzudo, Tomoaki

Metallurgical and Materials Transactions A, 52(1), p.257 - 269, 2021/01

https://doi.org/10.1007/s11661-020-06075-7

We simulated the thermal desorption spectra of a small-size iron specimen to which was applied during charging with hydrogen atoms using a model incorporating the behavior of vacancies and vacancy clusters. The model considered up to vacancy clusters , which is composed of nine vacancies and employed the parameters based on atomistic calculations, including the H trapping energy of vacancies and vacancy clusters that we estimated using the molecular static calculation. As a result, we revealed that the model could, on the whole, reproduced the experimental spectra except two characteristic differences, and also the dependence of the spectra on the aging temperature. By examining the cause of the differences, the possibilities that the diffusion of clusters of and is slower than the model and that vacancy clusters are generated by applying strain and H charging concurrently were indicated.

Atomistic simulation of phosphorus segregation to 3(111) symmetrical tilt grain boundary in -iron

Ebihara, Kenichi; Suzudo, Tomoaki

Modelling and Simulation in Materials Science and Engineering, 26(6), p.065005_1 - 065005_10, 2018/09

AA2018-0168.pdf:2.74MB

https://doi.org/10.1088/1361-651X/aace6a

Irradiation-induced grain boundary phosphorus segregation is an important factor for estimating the embrittlement of nuclear reactor pressure vessel steels, but the physical process of phosphorus migration to grain boundaries is still unclear. We numerically studied phosphorus migration toward 3(111) symmetrical tilt grain boundary in -iron using molecular dynamics. We found that, in the vicinity of the grain boundary within 1 nm distance, an iron-phosphorus mixed dumbbell and an octahedral interstitial phosphorus atom push a self-interstitial atom into the grain boundary, and the phosphorus atom becomes a substitutional atom. A phosphorus vacancy complex in the region also becomes dissociated, and the vacancy is absorbed in the grain boundary without dragging phosphorus. The results claim that a novel view of the segregation process is required.

Enhanced damage buildup in C-implanted GaN film studied by a monoenergetic positron beam

Li, X. F.*; Chen, Z. Q.*; Liu, C.*; Zhang, H.; Kawasuso, Atsuo

Journal of Applied Physics, 117(8), p.085706_1 - 085706_6, 2015/02

https://doi.org/10.1063/1.4913523

Vacancy-type defects in C-implanted GaN were probed using a slow positron beam. The increase of Doppler broadening S parameter indicates introduction of arge vacancy clusters. Post-implantation annealing at temperatures up to 800C makes these vacancy clusters to agglomerate into microvoids. The vacancy clusters or microvoids show high thermal stability, and they are only partially removed after annealing up to 1000C. Amorphous regions are observed by high resolution transmission electron microscopy measurement, which directly confirms that amorphization is induced by C-implantation. The disordered GaN lattice is possibly due to special feature of carbon impurities, which enhance the damage buildup during implantation.

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

https://doi.org/10.1016/j.physb.2005.12.090

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.

Divacancy model for P6/P7 centers in 4H- and 6H-SiC

Son, N. T.*; Umeda, Takahide*; Isoya, Junichi*; Gali, A.*; Bockstedte, M.*; Magnusson, B.*; Ellison, A.*; Morishita, Norio; Oshima, Takeshi; Ito, Hisayoshi; et al.

Materials Science Forum, 527-529, p.527 - 530, 2006/00

no abstracts in English

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

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

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

https://doi.org/10.1103/PhysRevB.71.193204

Electron-positron momentum distributions associated with vacancy defects in 6H SiC after irradiation with 2 MeV electrons and annealing at 1000 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.

EPR identification of two types of carbon vacancies in 4-SiC

Umeda, Takahide*; Isoya, Junichi*; Morishita, Norio; Oshima, Takeshi; Kamiya, Tomihiro

Physical Review B, 69(12), p.121201_1 - 121201_4, 2004/03

https://doi.org/10.1103/PhysRevB.69.121201

EI5 and EI6 centers in 4-SiC were studied using EPR. EI5 and EI6 centers were introduced by 3MeV-electron irradiation at 850 C. EI5 and EI6 were reported to be carbon vacancy with positive charge and silicon snti-site with positive charge, respectively. As a result of the angle dependence and temperature dependence measurement, both sites were identified to be carbon vacancies with positive charge. The defference between EI5 and EI6 is explained in terms of the difference of sites (like -site and -site) located in 4-SiC.

Postgrowth annealing on defects in ZnO studied by positron annihilation, X-ray diffraction, rutherford backscattering, cathodoluminescence and hall measurements

Chen, Z. Q.; Yamamoto, Shunya; Maekawa, Masaki; Kawasuso, Atsuo; Yuan, X. L.*; Sekiguchi, Takashi*

Journal of Applied Physics, 94(8), p.4807 - 4812, 2003/10

https://doi.org/10.1063/1.1609050

no abstracts in English

Polytype-dependent vacancy annealing studied by positron annihilation

Kawasuso, Atsuo; Yoshikawa, Masahito; Maekawa, Masaki; Ito, Hisayoshi; Chiba, Toshinobu*; Redmann, F.*; Rehberg, R. K.*; Weidner, M.*; Frank, T.*; Pensl, G.*

Materials Science Forum, 433-436, p.477 - 480, 2003/08

no abstracts in English

Continuous-wave and pulsed EPR study of the negatively charged silicon vacancy with S=3/2 and C symmetry in -type 4H-SiC

Mizuochi, Norikazu*; Yamasaki, Satoshi*; Takizawa, Haruki; Morishita, Norio; Oshima, Takeshi; Ito, Hisayoshi; Isoya, Junichi*

Physical Review B, 66(23), p.235202_1 - 235202_12, 2002/12

https://doi.org/10.1103/PhysRevB.66.235202

EPR study was performed to understand vacancy-type defects in electron-irradiated 4H-SiC. In this study, the T center which was reported to be S=1 was charactrized. As a result of untation method of EPR technique, it was revealed that the multipicity of the center is not triplet (S=1) but quartet (S=3/2). From the analysis of C hyperfine interactions of nearest-neighbors, the canter was determined to be single silicon vacancy. In addition, it was found that the center is negativly charged silicon vacancy with C symmetry.