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Journal Articles

High-rate crystallization of polycarbonate in spincast thin film

Ata, Seisuke*; Oka, Toshitaka; He, C.-Q.*; Odaira, Toshiyuki*; Suzuki, Ryoichi*; Ito, Kenji*; Kobayashi, Yoshinori*; Ougizawa, Toshiaki*

Journal of Polymer Science, Part B; Polymer Physics, 48(20), p.2148 - 2153, 2010/10

 Times Cited Count:4 Percentile:84.21(Polymer Science)

Surface morphology of bisphenol-A polycarbonate (BAPC) thin films with thickness ranging from 30 to 1000 nm on silicon substrates was studied by atomic force microscopy (AFM). The films were prepared by spincasting from 1,2-dichloroethane solutions of 0.25-5.0 wt % BAPC. Even though longer annealing than 250 h was necessary for complete crystallization for bulk BAPC, high crystallinity was observed for 30 nm thick film after annealing at 200 $$^{circ}$$C for 48 h in vacuum. Positron annihilation lifetime spectroscopy (PALS) measurements showed that the free volume hole size in 30 nm thick film was larger than that of bulk at 200 $$^{circ}$$C. Comparison of the BAPC concentration in the precursor solution with the overlap concentration suggests that the high crystallinity of the 30 nm BAPC film is due to less entangled chains caused by rapid removal of the solvent from the dilute solution.

Journal Articles

Positronium formation in fused quartz; Experimental evidence of delayed formation

Komuro, Yo; Hirade, Tetsuya; Suzuki, Ryoichi*; Odaira, Toshiyuki*; Muramatsu, Makoto*

Radiation Physics and Chemistry, 76(2), p.330 - 332, 2007/02

 Times Cited Count:3 Percentile:72.67(Chemistry, Physical)

Recently, positronium (Ps) formation mechanism in the spur is becoming clarified. Blob model, the modified Spur model, proposed by Stepanov can give information of Ps formation time. Dauwe et al. showed that S(t) curve of PMMA observed by AMOC measurement could be fitted by the blob model. The young-age broadening was found and explained with the delayed slowing down of Ps by Stuttgart group. The delayed Ps formation was shown by Suzuki et al. especially at low temperatures, because positrons can diffuse long distance to find trapped electrons. According to the blob model, Ps formation even after long diffusion of positrons might be possible even at the room temperature. Now we are trying to obtain the experimental evidence of delayed Ps formation in spur process.

Journal Articles

Application of high-energy photon beam to industrial imaging based on positron annihilation

Toyokawa, Hiroyuki*; Hirade, Tetsuya; Kuroda, Ryunosuke*; Suzuki, Ryoichi*; Odaira, Toshiyuki*

Proceedings of 8th International Topical Meeting on Nuclear Applications and Utilization of Accelerators (AccApp '07) (CD-ROM), p.331 - 335, 2007/00

A novel radiographic method for nondestructive testing of industrial products based on positron annihilation was presented. High-energy $$gamma$$-ray beam, which was generated via the laser-Compton scattering was used for the present method. An experimental study using a reinforced concrete block, as a sample, showed that the method was suitable for nondestructive testing of industrial products containing metals. Tomographic method was also applied, and a cross-sectional image of the sample was obtained. By use of high-energy $$gamma$$-ray beam, we can detect not only the decay of $$gamma$$-ray beam and also the decay of annihilation $$gamma$$-rays from positrons formed in the samples. By shifting and rotating the sample, it is possible to obtain PET (positron emission tomography) image. It is also expected that positron annihilation method can be applied for the certain cite in the sample.

Journal Articles

Defect layer in SiO$$_2$$-SiC interface proved by a slow positron beam

Maekawa, Masaki; Kawasuso, Atsuo; Yoshikawa, Masahito; Miyashita, Atsumi; Suzuki, Ryoichi*; Odaira, Toshiyuki*

Physica B; Condensed Matter, 376-377, p.354 - 357, 2006/04

 Times Cited Count:2 Percentile:86.49(Physics, Condensed Matter)

no abstracts in English

Journal Articles

Structure of SiO$$_2$$/4H-SiC interface probed by positron annihilation spectroscopy

Maekawa, Masaki; Kawasuso, Atsuo; Yoshikawa, Masahito; Miyashita, Atsumi; Suzuki, Ryoichi*; Odaira, Toshiyuki*

Physical Review B, 73(1), p.014111_1 - 014111_9, 2006/01

 Times Cited Count:19 Percentile:34.56(Materials Science, Multidisciplinary)

no abstracts in English

Journal Articles

Interaction of nitrogen with vacancy defects in N$$^{+}$$-implanted ZnO studied using a slow positron beam

Chen, Z. Q.; Maekawa, Masaki; Kawasuso, Atsuo; Suzuki, Ryoichi*; Odaira, Toshiyuki*

Applied Physics Letters, 87(9), p.091910_1 - 091910_3, 2005/08

 Times Cited Count:28 Percentile:29.06(Physics, Applied)

Zinc oxide crystals were implanted with N$$^+$$, O$$^+$$, and co-implanted with O$$^+$$/N$$^+$$ ions. Positron annihilation measurements show the introduction of vacancy clusters upon implantation. In the N$$^+$$-implanted sample, these vacancy clusters are only partially annealed at 800$$^{circ}$$C as compared to their full recovery in the O$$^+$$-implanted sample, suggesting a strong interaction between nitrogen and vacancy clusters. At 1000-1100$$^{circ}$$C, nitrogen also forms stable complexes with thermally generated vacancies. To remove all the detectable vacancy defects, a high temperature annealing at 1250$$^{circ}$$C is needed. Furthermore, Hall measurements of this sample show n-type conductivity though nitrogen is expected as acceptors. On the contrary, in the O$$^+$$/N$$^+$$ co-implanted sample, most vacancy clusters disappear at 800$$^{circ}$$C. Probably oxygen scavenges nitrogen to form N-O complexes and hence enhance the annealing of vacancy clusters. A highly compensated semi-insulating layer is formed in the co-implanted sample.

Journal Articles

Structural defects in SiO$$_2$$/SiC interface probed by a slow positron beam

Maekawa, Masaki; Kawasuso, Atsuo; Chen, Z. Q.; Yoshikawa, Masahito; Suzuki, Ryoichi*; Odaira, Toshiyuki*

Applied Surface Science, 244(1-4), p.322 - 325, 2005/05

 Times Cited Count:11 Percentile:52.63(Chemistry, Physical)

no abstracts in English

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:100 Percentile:5.84(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:132 Percentile:3.68(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

Positron annihilation methods by $$gamma$$-rays produced in laser-induced compton-backscattering

Hirade, Tetsuya; Toyokawa, Hiroyuki*; Odaira, Toshiyuki*; Suzuki, Ryoichi*; Ogaki, Hideaki*

Materials Science Forum, 445-446, p.474 - 476, 2004/02

Positron annihilation methods are very unique and strong tools to investigate materials. However, positrons are usually injected from outside of the samples. Therefore the samples should be in a vacuum or radioisotopes should be attached. Recently, Selim et al. applied high-energy g-rays (2MeV) produced by use of 6MeV electron linac to create positrons in thick materials. We have also been trying a similar method. In our case, high-energy $$gamma$$-rays ($$sim$$20MeV) produced in laser-induced Compton-backscattering are applied for positron creation in samples. The $$gamma$$-rays do not spread and penetrate straightly in air. When you place a sample on the path of $$gamma$$-rays, positrons are created in the sample and usual positron annihilation methods can be applied. Moreover, It is not needed to place the samples in vacuum and radioisotopes are not necessary. It means that the measurements of very high temperature materials such as metals near/over melting points will be possible. The detail of this method and some examples of experimental results will be introduced.

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:5.95(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

Crystallization of an amorphous layer in P$$^{+}$$-implanted 6H-SiC studied by monoenergetic positron beams

Uedono, Akira*; Tanigawa, Shoichiro*; Oshima, Takeshi; Ito, Hisayoshi; Yoshikawa, Masahito; Nashiyama, Isamu; Frank, T.*; Pensl, G.*; Suzuki, Ryoichi*; Odaira, Toshiyuki*; et al.

Journal of Applied Physics, 87(9), p.4119 - 4125, 2000/05

 Times Cited Count:12 Percentile:49.33(Physics, Applied)

no abstracts in English

Journal Articles

Study of residual defects in ion-implanted and subsequently annealed 3C-SiC

Oshima, Takeshi; Ito, Hisayoshi; Uedono, Akira*; Suzuki, Ryoichi*; Ishida, Yuki*; Takahashi, Tetsuo*; Yoshikawa, Masahito; Kojima, Kazutoshi; Odaira, Toshiyuki*; Nashiyama, Isamu; et al.

Denshi Gijutsu Sogo Kenkyujo Iho, 62(10-11), p.469 - 476, 1999/00

no abstracts in English

Oral presentation

Positronium formation in SiO$$_{2}$$

Komuro, Yo; Hirade, Tetsuya; Suzuki, Ryoichi*; Odaira, Toshiyuki*; Muramatsu, Makoto*

no journal, , 

The annihilation $$gamma$$ rays from the para-pojitoronium (p-Ps) state gives narrower Doppler broadening. The broader Doppler broadening was observed at very young age region that is mainly from the annihilation process of p-Ps. It was explained by the delayed Ps slowing down and the delayed Ps formation. We have successfully obtained the experimental evidence of the delayed Ps formation.

Oral presentation

Evidence of the delayed positronium formation in fused quartz

Komuro, Yo; Hirade, Tetsuya; Suzuki, Ryoichi*; Odaira, Toshiyuki*; Muramatsu, Makoto*; Suzuki, Takenori*

no journal, , 

Many ions and the excess electrons are formed by the injected positron just before the thermalization of that positron in a small area (it is called spur or blob) in condensed matter. The positron has a chance to form positronium (Ps) with one of the excess electrons. According to the model of Ps formation in the spur (blob), the initial encounter pairs of an electron and a positron will form Ps in short time. Some of the positrons have some possibility to form Ps after diffusion in several hundreds pico-seconds. There were experimental results that were interpreted as a Ps thermalization by a group in Germany more than 10 years ago. However, we have believed that some of the results were caused by the delayed Ps formation and have successfully obtained the experimental evidence of the delayed Ps formation by applying electric fields on the sample, fused quartz.

Oral presentation

Positronium formation at the terminal spur of positron track; Delayed positronium formation in fused quartz

Komuro, Yo; Hirade, Tetsuya; Suzuki, Ryoichi*; Odaira, Toshiyuki*; Muramatsu, Makoto*; Suzuki, Takenori*

no journal, , 

The injected positrons to condensed materials form a very small area where they deposit much energy and some tens of ion-electron pairs are formed. This area is called a positron spur or blob. Positrons have a possibility to form positronium at this area. Some of the positrons are isolated from the excess electrons when they thermalized. They will have smaller possibility to form positronium and longer time to form positronium. Therefore the positronium formation by the isolated positrons from excess electrons can be easily inhibited by applying the external electric fields. We have found this expected phenomena by applying the external electric fields.

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