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Journal Articles

The Project for grouting development for high level radioactive waste repository, 3; Study of allowable seepage water quantity by permiability test though contact face of buffer material blocks

Sekine, Ichiro*; Yamada, Tsutomu*; Sekiguchi, Takashi*; Fujita, Tomo; Nakanishi, Tatsuro

Doboku Gakkai Heisei-23-Nendo Zenkoku Taikai Dai-66-Kai Nenji Gakujutsu Koenkai Koen Gaiyoshu (DVD-ROM), p.69 - 70, 2011/09

no abstracts in English

Journal Articles

The Project for grouting development for high level radioactive waste repository, 4; Development of superfine spherical silica grout

Yamada, Tsutomu*; Sekine, Ichiro*; Sekiguchi, Takashi*; Ishida, Hideaki*; Kishi, Hirokazu; Fukuoka, Naomi

Doboku Gakkai Heisei-22-Nendo Zenkoku Taikai Dai-65-Kai Nenji Gakujutsu Koenkai Koen Gaiyoshu (DVD-ROM), p.89 - 90, 2010/09

no abstracts in English

Journal Articles

Thermal evolution of defects in as-grown and electron-irradiated ZnO studied by positron annihilation

Chen, Z. Q.*; Wang, S. J.*; Maekawa, Masaki; Kawasuso, Atsuo; Naramoto, Hiroshi*; Yuan, X. L.*; Sekiguchi, Takashi*

Physical Review B, 75(24), p.245206_1 - 24520_9, 2007/06

 Times Cited Count:61 Percentile:88.76(Materials Science, Multidisciplinary)

Vacancy-type defects in as-grown ZnO single crystals have been identified using positron annihilation spectroscopy. The grown-in defects are supposed to be zinc vacancy V$$_{Zn}$$-related defects, and can be easily removed by annealing above 600$$^{circ}$$C. V$$_{Zn}$$-related defects are also introduced in ZnO when subjected to 3 MeV electron irradiation with a dose of 5.5$$times$$10$$^{18}$$ cm$$^{-2}$$. Most of these irradiation-induced V$$_{Zn}$$ are annealed at temperatures below 200$$^{circ}$$C through recombination with the close interstitials. However, after annealing at around 400$$^{circ}$$C, secondary defects are generated. A detailed analysis of the Doppler broadening measurements indicates that the irradiation introduced defects and the annealing induced secondary defects belong to different species. It is also found that positron trapping by these two defects has different temperature dependences. The probable candidates for the secondary defects are tentatively discussed in combination with Raman scattering studies. After annealing at 700$$^{circ}$$C, all the vacancy defects are annealed out. Cathodoluminescence measurements show that V$$_{Zn}$$ is not related to the visible emission at 2.3 eV in ZnO, but would rather act as nonradiative recombination centers.

Journal Articles

Characterization of homoepitaxial and heteroepitaxial ZnO films grown by pulsed laser deposition

Chen, Z. Q.; Yamamoto, Shunya; Kawasuso, Atsuo; Xu, Y. H.; Sekiguchi, Takashi*

Applied Surface Science, 244(1-4), p.377 - 380, 2005/05

 Times Cited Count:16 Percentile:57.32(Chemistry, Physical)

Homo- and heteroepitaxial ZnO films were grown by pulsed laser deposition on single crystal ZnO substrate and Al$$_2$$O$$_3$$ substrate, respectively. The surface roughness probed by atomic force microscope (AFM) depends strongly on the substrate, which is much larger for the heteroepitaxial layer. Doppler broadening of positron annihilation measurements show existence of defects in both of the films, with a higher concentration in the homoepitaxial film. Raman scattering measurements reveal the E2 phonon vibration mode at 437 cm$$^{-1}$$, which is characteristic of the wurtzite structure. These films show strong ultraviolet (UV) emission at 3.3 eV from the cathodoluminescence measurements, which indicates good optical properties.

Journal Articles

Microvoid formation in hydrogen-implanted ZnO probed by a slow positron beam

Chen, Z. Q.; Kawasuso, Atsuo; Xu, Y.; Naramoto, Hiroshi*; Yuan, X. L.*; Sekiguchi, Takashi*; Suzuki, Ryoichi*; Odaira, Toshiyuki*

Physical Review B, 71(11), p.115213_1 - 115213_8, 2005/03

 Times Cited Count:101 Percentile:94.02(Materials Science, Multidisciplinary)

ZnO crystals were implanted with 20-80 keV hydrogen ions up to a total dose of 4.4$$times$$10$$^{15}$$ cm$$^{-2}$$. Positron annihilation measurements show introduction of zinc vacancies, which are filled with hydrogen atoms. After isochronal annealing at 200-500 $$^{circ}$$C, the vacancies agglomerate into hydrogen bubbles. Further annealing at 600-700 $$^{circ}$$C causes release of hydrogen out of the bubbles, leaving large amount of microvoids. These microvoids are annealed out at high temperature of 1000 $$^{circ}$$C. Cathodoluminescence measurements reveal that hydrogen ions also passivate deep level emission centers before their release from the sample, and lead to the improvement of the UV emission.

Journal Articles

Production and recovery of defects in phosphorus-implanted ZnO

Chen, Z. Q.; Kawasuso, Atsuo; Xu, Y.; Naramoto, Hiroshi; Yuan, X. L.*; Sekiguchi, Takashi*; Suzuki, Ryoichi*; Odaira, Toshiyuki*

Journal of Applied Physics, 97(1), p.013528_1 - 013528_6, 2005/01

 Times Cited Count:135 Percentile:96.29(Physics, Applied)

Phosphorus ions were implanted into ZnO crystals with energies of 50-380 keV to a dose of 10$$^{13}$$-10$$^{15}$$ cm$$^{-2}$$. Positron annihilation measurements show the introduction of vacancy clusters after implantation. These vacancy clusters evolve to microvoids after annealing at a temperature of 600$$^{circ}$$C, and disappear gradually up to 1100$$^{circ}$$C. Raman scattering measurements show the production of oxygen vacancies (V$$_{O}$$). They are annealed up to 700$$^{circ}$$C accompanying the agglomeration of vacancy clusters. The light emissions of ZnO are suppressed due to the competing nonradiative recombination centers introduced by implantation. Recovery of the light emission occurs above 600$$^{circ}$$C. The vacancy-type defects detected by positrons might be part of the nonradiative recombination centers. Hall measurement shows n-type conductivity for the P$$^+$$-implanted ZnO layer, which suggests that phosphorus is an amphoteric dopant.

Journal Articles

Hydrogen bubble formation in H-implanted ZnO studied using a slow positron beam

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

JAERI-Review 2004-025, TIARA Annual Report 2003, p.193 - 195, 2004/11

20-80 keV hydrogen ions were implanted into ZnO single crystals up to a total dose of 4.4$$times$$10$$^{15}$$ cm$$^{-2}$$. Positron annihilation measurements using a slow positron beam revealed introduction of vacancies after implantation, which are filled with hydrogen impurities. After annealing, these hydrogen filled vacancies grow into large hydrogen bubbles. At annealing temperature of 500-700$$^{circ}$$C, these hydrogen impurities are released from the bubbles, and remain open microvoids. These microvoids are finally annealed out at about 1100$$^{circ}$$C. The effects of hydrogen implantation on the light luminescence in ZnO will also be discussed.

Journal Articles

N$$^+$$ ion-implantation-induced defects in ZnO studied with a slow positron beam

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

Journal of Physics; Condensed Matter, 16(2), p.S293 - S299, 2004/01

 Times Cited Count:25 Percentile:73(Physics, Condensed Matter)

Undoped ZnO single crystals were implanted with multiple energy N$$^+$$ ions ranging from 50 to 380 keV with dose from 10$$^{12}$$/cm$$^2$$ to 10$$^{14}$$/cm$$^2$$. Positron annihilation measurements show that vacancy defects are introduced in the implanted layers. The concentration of the vacancy defects increases with increasing ion dose. Annealing behavior of the defects can be divided into four stages, which correspond to the formation and recovery of large vacancy clusters, formation and disappearance of vacancy-impurity complexes, respectively. All the implantation induced defects are removed by annealing at 1200$$^{circ}$$C. Cathodoluminescence measurements show that the ion implantation induced defects act as nonradiative recombination centers to suppress the ultraviolet emission. After annealing, these defects disappear gradually and the ultraviolet emission reappears, which coincides with positron annihilation measurement. The Hall measurements reveal that after N$$^+$$-implantation, the ZnO layer still shows n-type conductivity.

Journal Articles

Evolution of voids in Al$$^+$$-implanted ZnO probed by a slow positron beam

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

Physical Review B, 69(3), p.035210_1 - 035210_10, 2004/01

 Times Cited Count:89 Percentile:93.88(Materials Science, Multidisciplinary)

Introduction and annealing behavior of defects in Al$$^+$$-implanted ZnO have been studied using energy variable slow positron beam. Vacancy clusters are produced after Al$$^+$$-implantation. With increasing ion dose above 10$$^{14}$$ Al$$^+$$/cm$$^2$$ the implanted layer is amorphized. Heat treatment up to 600 $$^{circ}$$C enhances the creation of large voids that allow the positronium formation. The large voids disappear accompanying the recrystallization process by the further heat treatment above 600 $$^{circ}$$C. Afterwards, implanted Al impurities are completely activated to contribute the n-type conduction. The ZnO crystal quality is also improved after recrystallization.

Journal Articles

Ion-implantation induced defects in ZnO studied by s slow positron beam

Chen, Z. Q.; Maekawa, Masaki; Sekiguchi, Takashi*; Suzuki, Ryoichi*; Kawasuso, Atsuo

Materials Science Forum, 445-446, p.57 - 59, 2004/00

no abstracts in English

Journal Articles

Study of ion beam induced defects in ZnO by using slow positron beam

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

JAERI-Review 2003-033, TIARA Annual Report 2002, p.209 - 211, 2003/11

Undoped ZnO crystals were implanted with Al$$^+$$, N$$^+$$ and Al$$^+$$/N$$^+$$ respectively. The implantation induced defects and their recovery were studied using a variable energy slow positron beam. Vacancy clusters are introduced in all the implanted samples. The annealing of the defects in Al$$^+$$-implanted sample shows two stages, which might be due to the agglomeration of vacancy clusters and their recovery, respectively. Large voids are also observed when the Al$$^+$$ dose is higher than 10$$^{14}$$ cm$$^{-2}$$, which suggest amorphization of ZnO. However, for both the N$$^+$$-implanted and the Al$$^+$$/N$$^+$$ co-implanted sample, the annealing behavior of the defects shows four stages. The last two stages might be related with the formation and recovery of nitrogen related defect complexes. Hall measurements show a strong n-type conductive layer after Al$$^+$$ implantation and annealing, suggesting that all the Al$$^+$$ ions are activated. However, for the N$$^{+}$$-implanted and Al$$^+$$/N$$^+$$ co-implanted ZnO, the implanted layer still shows n-type conductivity. The possible reason is discussed.

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:162 Percentile:96.86(Physics, Applied)

no abstracts in English

Journal Articles

Performance study of the cryogenic system for ITER CS model coil

Kato, Takashi; Hamada, Kazuya; Kawano, Katsumi; Matsui, Kunihiro; Hiyama, Tadao; Nishida, Kazuhiko*; Honda, Tadaaki*; Taneda, Masanobu*; Sekiguchi, Shuichi*; Otsu, Kiichi*; et al.

ICEC16/ICMC Proceedings, p.127 - 130, 1996/00

no abstracts in English

Oral presentation

The Project for grouting technology development for the high level radioactive waste repository, 6; Fundamental property test on the superfine silica powder as grouting material

Sekiguchi, Takashi*; Sekine, Ichiro*; Tomizawa, Naomi*; Hirano, Kenkichi*; Ishida, Hideaki*; Fujita, Tomo; Yamada, Tsutomu

no journal, , 

no abstracts in English

Oral presentation

Corrosion behavior of Ni-based alloy in molten FLiNaK salt as a fundamental research on molten salt reactors

Ogasawara, Koji*; Sekiguchi, Yuma*; Terai, Takayuki*; Kawamura, Hiroshi*; Tsuchiya, Kunihiko; Watanabe, Takashi*

no journal, , 

no abstracts in English

Oral presentation

Study on evaluation method for aerosol particle behavior in a reactor building, 3; Evaluation of aerosol particle behavior based on CFD simulation, and effect of gas flow rate and particle diameter

Horiguchi, Naoki; Nakamura, Koichi*; Sekiguchi, Takashige*; Uesawa, Shinichiro; Himi, Masashi*; Yoshida, Hiroyuki; Nishimura, Satoshi*

no journal, , 

no abstracts in English

Oral presentation

Investigation of hydration and adsorption structures of radium by EXAFS

Yamaguchi, Akiko; Nagata, Kojiro*; Tanaka, Kazuya; Kobayashi, Keita; Okumura, Masahiko; Kobayashi, Toru; Shimojo, Kojiro; Tanida, Hajime; Sekiguchi, Tetsuhiro; Kaneta, Yui; et al.

no journal, , 

no abstracts in English

Oral presentation

Investigation of hydration and adsorption structures on clay minerals of radium

Yamaguchi, Akiko; Nagata, Kojiro*; Tanaka, Kazuya; Kobayashi, Keita; Okumura, Masahiko; Kobayashi, Toru; Shimojo, Kojiro; Tanida, Hajime; Sekiguchi, Tetsuhiro; Kaneta, Yui; et al.

no journal, , 

no abstracts in English

18 (Records 1-18 displayed on this page)
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