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molecular dynamics simulations reveal the hydration structure of the radium(II) ionYamaguchi, Akiko; Nagata, Kojiro*; Kobayashi, Keita; Tanaka, Kazuya; Kobayashi, Toru; Tanida, Hajime; Shimojo, Kojiro; Sekiguchi, Tetsuhiro; Kaneta, Yui; Matsuda, Shohei; et al.
iScience (Internet), 25(8), p.104763_1 - 104763_12, 2022/08
Times Cited Count：15 Percentile：72.14(Multidisciplinary Sciences)no abstracts in English
Yamaguchi, Akiko; Nagata, Kojiro*; Tanaka, Kazuya; Kobayashi, Keita; Kobayashi, Toru; Shimojo, Kojiro; Tanida, Hajime; Sekiguchi, Tetsuhiro; Kaneta, Yui; Matsuda, Shohei; et al.
Hosha Kagaku, (45), p.28 - 30, 2022/03
no abstracts in English
Sekine, Ichiro*; Yamada, Tsutomu*; Sekiguchi, Takashi*; Fujita, Tomoo; 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
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
implanted silicon oxide thin films upon annealing treatmentsYu, R. S.*; Maekawa, Masaki; Kawasuso, Atsuo; Sekiguchi, Takashi*; Wang, B. Y.*; Qin, X. B.*; Wang, Q. Z.*
Nuclear Instruments and Methods in Physics Research B, 267(18), p.3097 - 3099, 2009/09
The structural evolution of silicon oxide films with Germanium implantation was traced with a positron beam equipped with positron annihilation Doppler broadening and lifetime spectrometers. Results indicate that the film structure change as a function of the annealing temperature could be divided into four stages: (I) T 
300
C; (II) 300C T 500C; (III) 600C T 800C; (IV) T 
900C. In comparison with stage I, the increased positron annihilation Doppler broadening S values during stage II is ascribed to the annealing out of point defects and coalescence of intrinsic open volumes in silicon oxides. The obtained long positron lifetime and high S values without much fluctuation in stage III suggest a rather stable film structure. Further annealing above 900C brings about dramatic change of the film structure with Ge precipitation. Positron annihilation spectroscopy is thereby a sensitive probe for the diagnosis of microstructure variation of silicon oxide thin films with nano-precipitation.
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：87.02(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
-related defects, and can be easily removed by annealing above 600C. V-related defects are also introduced in ZnO when subjected to 3 MeV electron irradiation with a dose of 5.5
10
cm
. Most of these irradiation-induced V are annealed at temperatures below 200C through recombination with the close interstitials. However, after annealing at around 400C, 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 700C, all the vacancy defects are annealed out. Cathodoluminescence measurements show that V is not related to the visible emission at 2.3 eV in ZnO, but would rather act as nonradiative recombination centers.
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：55.06(Chemistry, Physical)Homo- and heteroepitaxial ZnO films were grown by pulsed laser deposition on single crystal ZnO substrate and Al
O
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
, 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.
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：106 Percentile：93.48(Materials Science, Multidisciplinary)ZnO crystals were implanted with 20-80 keV hydrogen ions up to a total dose of 4.410
cm. Positron annihilation measurements show introduction of zinc vacancies, which are filled with hydrogen atoms. After isochronal annealing at 200-500 C, the vacancies agglomerate into hydrogen bubbles. Further annealing at 600-700 C causes release of hydrogen out of the bubbles, leaving large amount of microvoids. These microvoids are annealed out at high temperature of 1000 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.
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：150 Percentile：96.38(Physics, Applied)Phosphorus ions were implanted into ZnO crystals with energies of 50-380 keV to a dose of 10
-10 cm. Positron annihilation measurements show the introduction of vacancy clusters after implantation. These vacancy clusters evolve to microvoids after annealing at a temperature of 600C, and disappear gradually up to 1100C. Raman scattering measurements show the production of oxygen vacancies (V
). They are annealed up to 700C 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 600C. 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.
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 4.410 cm. 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 500-700C, these hydrogen impurities are released from the bubbles, and remain open microvoids. These microvoids are finally annealed out at about 1100C. The effects of hydrogen implantation on the light luminescence in ZnO will also be discussed.
ion-implantation-induced defects in ZnO studied with a slow positron beamChen, 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：70.95(Physics, Condensed Matter)Undoped ZnO single crystals were implanted with multiple energy N ions ranging from 50 to 380 keV with dose from 10
/cm
to 10
/cm. 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 1200C. 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.
-implanted ZnO probed by a slow positron beamChen, 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：92 Percentile：93.35(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 Al/cm the implanted layer is amorphized. Heat treatment up to 600 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 C. Afterwards, implanted Al impurities are completely activated to contribute the n-type conduction. The ZnO crystal quality is also improved after recrystallization.
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
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 cm, 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.
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：170 Percentile：96.64(Physics, Applied)no abstracts in English
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
Sekiguchi, Takashi*; Sekine, Ichiro*; Tomizawa, Naomi*; Hirano, Kenkichi*; Ishida, Hideaki*; Fujita, Tomoo; Yamada, Tsutomu
no journal, ,
no abstracts in English
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
Ogasawara, Koji*; Sekiguchi, Yuma*; Terai, Takayuki*; Kawamura, Hiroshi*; Tsuchiya, Kunihiko; Watanabe, Takashi*
no journal, ,
no abstracts in English
Horiguchi, Naoki; Nakamura, Koichi*; Sekiguchi, Takashige*; Uesawa, Shinichiro; Himi, Masashi*; Yoshida, Hiroyuki; Nishimura, Satoshi*
no journal, ,
no abstracts in English
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
