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Journal Articles

Study on simulation of thermal desorption spectra for a tempered martensitic steel with vacancies induced by hydrogen and strain

Ebihara, Kenichi; Saito, Kei*; Takai, Kenichi*

"Suiso Zeika No Kihon Yoin To Tokusei Hyoka" Kenkyukai Hokokusho, p.57 - 61, 2018/09

no abstracts in English

Journal Articles

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

Ebihara, Kenichi; Suzudo, Tomoaki

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

 Times Cited Count:1 Percentile:81.73(Materials Science, Multidisciplinary)

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 $$Sigma$$3(111) symmetrical tilt grain boundary in $$alpha$$-iron using molecular dynamics. We found that, in the vicinity of the grain boundary within $$sim$$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.

Journal Articles

Study on modeling of thermal desorption spectra of hydrogen including variation of vacancy-type trap sites

Ebihara, Kenichi; Saito, Kei*; Takai, Kenichi*

"Suiso Zeika No Kihon Yoin To Tokusei Hyoka Kenkyukai Chukan Hokokukai" Shimposium Yokoshu (USB Flash Drive), p.30 - 35, 2016/09

no abstracts in English

Journal Articles

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

 Times Cited Count:20 Percentile:21.41(Physics, Applied)

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 800$$^{circ}$$C 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 1000$$^{circ}$$C. 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.

Journal Articles

Identification of divacancies in 4H-SiC

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

Physica B; Condensed Matter, 376-377, p.334 - 337, 2006/04

 Times Cited Count:3 Percentile:80.39(Physics, Condensed Matter)

no abstracts in English

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:10 Percentile:52.48(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

Relationship between defects induced by irradiation and reduction of hole concentration in Al-doped 4H-SiC

Matsuura, Hideharu*; Kagamihara, So*; Ito, Yuji*; Oshima, Takeshi; Ito, Hisayoshi

Physica B; Condensed Matter, 376-377, p.342 - 345, 2006/04

 Times Cited Count:7 Percentile:61.99(Physics, Condensed Matter)

no abstracts in English

Journal Articles

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

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:14 Percentile:44.98(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:42.95(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

EPR and theoretical studies of positively charged carbon vacancy in 4$$H$$-SiC

Umeda, Takahide*; Isoya, Junichi*; Morishita, Norio; Oshima, Takeshi; Kamiya, Tomihiro; Gali, A.*; De$'a$k, P.*; Son, N. T.*; Janz$'e$n, E.*

Physical Review B, 70(23), p.235212_1 - 235212_6, 2004/12

 Times Cited Count:39 Percentile:16.41(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

EPR identification of two types of carbon vacancies in 4${it H}$-SiC

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

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

 Times Cited Count:44 Percentile:14.21(Materials Science, Multidisciplinary)

EI5 and EI6 centers in 4${it H}$-SiC were studied using EPR. EI5 and EI6 centers were introduced by 3MeV-electron irradiation at 850 $$^{circ}$$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 ${it k}$-site and ${it h}$-site) located in 4${it H}$-SiC.

Journal Articles

Vacancy defects detected by positron annihilation

Kawasuso, Atsuo; Weidener, M.*; Redmann, F.*; Frank, T.*; Sperr, P.*; K$"o$gel, G.*; Yoshikawa, Masahito; Ito, Hisayoshi; Krause-Rehberg, R.*; Triftsh$"a$user, W.*; et al.

Silicon Carbide, p.563 - 584, 2004/00

no abstracts in English

Journal Articles

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

 Times Cited Count:159 Percentile:2.94(Physics, Applied)

no abstracts in English

Journal Articles

EPR studies of the isolated negatively charged silicon vacancies in ${it n}$-type 4${it H}$- and 6${it H}$-SiC; Identification of ${it C}$$$_{3v}$$ symmetry and silicon sites

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

Physical Review B, 68(16), p.165206_1 - 165206_11, 2003/10

 Times Cited Count:36 Percentile:17.21(Materials Science, Multidisciplinary)

Isolated silicon vacancies with negative charge (V$$_{Si}$$$$^{-}$$) in 4H- and 6H-SiC were studied using EPR. The samples used in this study were irradiated with electron at 3 MeV at RT. After irradiation, the samples were annealed at 300 $$^{circ}$$C in Ar to eliminate C-related isolated vacancies. As the result of $$^{13}$$C hyperfine spectra, two kinds of V$$_{Si}$$$$^{-}$$(I) and V$$_{Si}$$$$^{-}$$(II) were distinguished and they are assigned to be arising from hexagonal and cubic sites of Si. In addition, both V$$_{Si}$$$$^{-}$$(I) and V$$_{Si}$$$$^{-}$$(II) signals have C$$_{3v}$$ symmetry, which means nearest-neighbor carbon atoms silightly distorted from a regular tetrahedron.

Journal Articles

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

Journal Articles

Annealing of vacancy-type defect and diffusion of implanted boron in 6H-SiC

Oshima, Takeshi; Uedono, Akira*; Eryu, Osamu*; Lee, K. K.; Abe, Koji*; Ito, Hisayoshi; Nakashima, Kenshiro*

Materials Science Forum, 433-436, p.633 - 636, 2003/08

no abstracts in English

Journal Articles

Continuous-wave and pulsed EPR study of the negatively charged silicon vacancy with S=3/2 and C$$_{3nu}$$ symmetry in $$n$$-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

 Times Cited Count:88 Percentile:5.46(Materials Science, Multidisciplinary)

EPR study was performed to understand vacancy-type defects in electron-irradiated 4H-SiC. In this study, the T$$_{V2a}$$ 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 $$^{13}$$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$$_{3nu}$$ symmetry.

Journal Articles

Annealing behavior of vacancies and Z$$_{1/2}$$ levels in electron-irradiated 4H-SiC studied by positron annihilation and deep-level transient spectroscopy

Kawasuso, Atsuo; Redmann, F.*; Krause-Rehberg, R.*; Weidner, M.*; Frank, T.*; Pensl, G.*; Sperr, P.*; Triftsh$"a$user, W.*; Ito, Hisayoshi

Applied Physics Letters, 79(24), p.3950 - 3952, 2001/12

 Times Cited Count:38 Percentile:19.19(Physics, Applied)

no abstracts in English

Journal Articles

Illumination effects in irradiated 6H n-type SiC observed by positron annihilation spectroscopy

Redmann, F.*; Kawasuso, Atsuo; Petters, K.*; Ito, Hisayoshi; Krause-Rehberg, R.*

Physica B; Condensed Matter, 308-310, p.629 - 632, 2001/12

 Times Cited Count:3 Percentile:75.57

no abstracts in English

70 (Records 1-20 displayed on this page)