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Journal Articles

Hydrogen desorption spectra from excess vacancy-type defects enhanced by hydrogen in tempered martensitic steel showing quasi-cleavage fracture

Saito, Kei*; Hirade, Tetsuya; Takai, Kenichi*

Metallurgical and Materials Transactions A, 50(11), p.5091 - 5102, 2019/11

 Times Cited Count:1 Percentile:53.51(Materials Science, Multidisciplinary)

An attempt was made to separate and identify hydrogen peaks desorbed from lattice defects formed by plastic-strain in the presence of hydrogen in tempered martensitic steel showing quasi-cleavage fracture using thermal desorption spectroscopy from a low temperature (L-TDS) and positron annihilation spectroscopy (PAS). The L-TDS results made it possible to separate two peaks, namely, that of the original desorption and also that of new desorption. The PAS results revealed that the new desorption obtained by L-TDS corresponded to vacancy-type defects. Hydrogen enhanced vacancy-type defect concentration, approximately 10$$^{-5}$$ order in terms of atomic ratio, formed within 1.5 mm from the fracture surface, These results indicate that the accumulation of excess vacancy-type defects enhanced by hydrogen in the local region can lead to nanovoid nucleation and coalescence in plastic deformation, resulting in quasi-cleavage fracture of tempered martensitic steel.

Journal Articles

Detector identification by waveform shape analysis for effective data acquisition: Improvements in time resolution and count rate for positron annihilation age-momentum correlation measurement

Hirade, Tetsuya; Ando, Hirokazu*; Manabe, Kensuke*; Ueda, Daisuke*

Nuclear Instruments and Methods in Physics Research A, 931, p.100 - 104, 2019/07

 Times Cited Count:1 Percentile:39.69(Instruments & Instrumentation)

A detector identification method using waveform-shape analysis is proposed. A method for enabling discrimination of detectors by making a characteristic waveform shape for every detector by each own loop circuit on the detector is shown as an example. This method can be applied in many experimental contexts with detectors, making a high counting rate possible. Moreover, detector identification can be used for other important questions such as detector position. As an example, this detector identification method is used to perform positron-annihilation age-momentum correlation measurement with a high temporal resolution and a high counting rate.

Journal Articles

Structure of nitride layer formed on titanium alloy surface by N$$_{2}$$-gas exposure at high temperatures

Takeda, Yusuke; Iida, Kiyoshi*; Sato, Shinji*; Matsuo, Tadatoshi*; Nagashima, Yasuyuki*; Okubo, Nariaki; Kondo, Keietsu; Hirade, Tetsuya

JPS Conference Proceedings (Internet), 25, p.011023_1 - 011023_3, 2019/03

In this study, we prepared samples under two different conditions, (1) 810$$^{circ}$$C, for 600 min, and (2) 850$$^{circ}$$C, for 720 min. A depth-profile analysis of the surfaces of the samples is conducted through Doppler broadening (DB) measurements of positron annihilation $$gamma$$ rays using a slow positron beam. It was indicated that many of positrons annihilated in defects near the surface. According to the TEM image, there are nano-crystal grains near the surface and then positrons can diffuse in the grains and annihilate in defects at the grain boundaries. Furthermore, DB measurements indicated that there is a depth dependence on the chemical composition where positrons annihilate. EDS spectroscopy measurements also indicated that there is a depth dependence of impurities such as Vanadium. These results indicated change of the chemical composition at the grain boundaries.

Journal Articles

Positronium in room temperature ionic liquids

Hirade, Tetsuya

Yodenshi Kagaku, (11), p.33 - 40, 2018/09

The positron injected in insulating materials thermalizes at the end part of its track and forms Positronium (Ps) with one of excess electrons within $$sim$$ 1 ps. Therefore, Ps formation can be a tool to investigate very fast processes like excess electron solvation in liquids. Many phenomena appeared in radiation chemistry researches for room temperature ionic liquids (ILs) are interesting and important for the application. Positron annihilation lifetime (PAL) measurements in ILs were carried out and anomalously long lifetime values of the shortest lifetime component were found in ILs. PAL and positron annihilation age-momentum correlation (AMOC) measurements were performed to clarify the reason of these anomalously long lifetime values and Ps bubble oscillation was finally discovered. Recent progresses are introduced with showing some results.

Journal Articles

Positron annihilation methods and applied researches for materials such as polymers

Hirade, Tetsuya

Kagaku To Kogyo, 92(2), p.44 - 54, 2018/02

A positron, an anti-particle of an electron, annihilates with an electron and emits energy that is proportional to mass energy as annihilation $$gamma$$-rays. Positron annihilation methods are applied by detecting these $$gamma$$-rays. The information of annihilation time, energy of $$gamma$$-rays, and direction of $$gamma$$-rays emission has been used for materials science. Here, positron annihilation lifetime, doppler broadening of annihilation $$gamma$$-rays and positron annihilation age-momentum correlation are mainly explained by use of research examples for metals and polymers, etc.

Journal Articles

Modern radiation chemistry (Applications), 24; Radiation chemistry and positron annihilation

Hirade, Tetsuya

Radioisotopes, 66(11), p.587 - 593, 2017/11

Positron, anti-particle of electron, annihilates with the lifetime of 100ps to several ns in condensed matter. The energy of the mass of both particles emits as two $$gamma$$-rays. The annihilation rate of energy of $$gamma$$-rays indicate information just before the annihilation. Positrons have some possibility of reaction with excess electrons to form Positronium (Ps). Ps formation occur within ~ps, therefore Ps formation can be a probe of very fast reactions. Moreover, long lived triplet Ps can have reaction with reactive species until the lifetime of ~ns. Here, methods of positron annihilation research for radiation chemistry and some researches done by positron annihilation methods are introduced.

Journal Articles

Positron annihilation in the near surface of room temperature ionic liquids

Hirade, Tetsuya; O'Rourke, B. E.*; Kobayashi, Yoshinori*

Journal of Physics; Conference Series, 791(1), p.012029_1 - 012029_4, 2017/02

 Times Cited Count:1 Percentile:100

We tried to observe the positron annihilation rates near surface of (room temperature ionic liquids) IL's, such as N,N,N-trimethyl-N-propylammonium bis(trifluoromethanesulfonyl)imide (TMPA-TFSI) by use of the perpendicular slow positron beamline installed at AIST. The vaper pressure of TMPA-TFSI is very small and hence it is possible to measure the positron annihilation rate in vacuum chamber directly. This represents the first energy variable experimental results of the positron annihilation rate at the near surface of an IL. The triplet positronium annihilation rate seems to be larger at nearer region to the surface of the IL's.

Journal Articles

Structure of nitride layer formed on titanium alloy surface by N$$_{2}$$-gas exposure at high temperatures

Takeda, Yusuke; Iida, Kiyoshi*; Sato, Shinji*; Matsuo, Tadatoshi*; Nagashima, Yasuyuki*; Okubo, Nariaki; Kondo, Keietsu; Hirade, Tetsuya

Journal of Physics; Conference Series, 791(1), p.012022_1 - 012022_4, 2017/02

 Times Cited Count:0 Percentile:100

Titanium alloy is widely used for applications such as golf club heads and structural materials for aircrafts. The surface can be exceedingly hardened by nitriding treatment that initiates defects, but there are some difficulties on use of titanium nitride because the layer can be exfoliated by stress. Therefore, we prepared samples in two different treatment conditions, (1) 810$$^{circ}$$C 600 min and (2) 850$$^{circ}$$C 720 min and performed depth profile analysis of Doppler broadening of positron annihilation $$gamma$$-rays (DB) for these samples. According to a calculation of nitrogen diffusion depth, the nitride layer should be only about 0.05-0.1$$mu$$m. However, the depth profile analysis of the DB measurement indicated that the defects introduced by nitriding treatment extended to a depth of 0.5$$mu$$m.

Journal Articles

Research and application of positronium chemistry

Hirade, Tetsuya

Hoshasen To Sangyo, (139), p.23 - 28, 2015/12

The researches and the applications of the Positronium Chemistry were introduced. The mechanism of Ps formation in low temperature insulators was clarified by Hirade and it is almost the end of the long, more than half century, period for arguments on Ps formation. Hence almost all of the researchers have been accepting the Spur Reaction Model proposed by Mogensen. Therefore, radiation chemistry researches by use of the Spur Reaction Model, especially the study of excess electrons at the time range of pico-to-nano second and electron mobility, were introduced. It was also introduced that the Free Volume Model is not correct and then the sub-nano meter vacant space, such as the microscopic free volume in polymers, can be studied by just the triplet Ps lifetime. As the latest research for the application, it was introduced that Ps bubble shows oscillation especially in ionic liquids and is expected to be a strong tool to investigate nano-scale properties of ionic liquids.

Journal Articles

Enhanced lattice defect formation associated with hydrogen and hydrogen embrittlement under elastic stress of a tempered martensitic steel

Doshida, Tomoki*; Suzuki, Hiroshi*; Takai, Kenichi*; Hirade, Tetsuya; Oshima, Nagayasu*

NanotechJapan Bulletin (Internet), 8(3), 5 Pages, 2015/07

Studying the creation and time evolution of defects is an important issue for interpreting the hydrogen embrittlement mechanism of steels. We have been studied the relationship between hydrogen embrittlement of high strength steel and lattice defects associated with hydrogen by thermal desorption analysis (TDA) and positron probe microanalyzer (PPMA).

Journal Articles

Positron annihilation age momentum correlation (AMOC) measurement

Hirade, Tetsuya

Yodenshi Kagaku, (4), p.3 - 8, 2015/02

Positron annihilation Age-MOmentum Correlation (AMOC) measurement is the coincidence measurement method of positron injection time, positron annihilation time and positron annihilation $$gamma$$-rays energy. The methods for measurement and analysis of AMOC will be introduced briefly. Some of the interesting researches also will be introduced.

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:52.55(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

Effect of ion species on the production and thermal evolution of implantation induced defects in ZnO

Chen, Z. Q.; Maekawa, Masaki; Kawasuso, Atsuo; Sakai, Seiji; Naramoto, Hiroshi*

JAEA-Review 2005-001, TIARA Annual Report 2004, p.232 - 234, 2006/01

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:27 Percentile:29.19(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

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:41.14(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

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:51.82(Chemistry, Physical)

no abstracts in English

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:43.09(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

Polymeric Co-C$$_{60}$$ compound phase evolved in atomistically mixed thin films

Sakai, Seiji; Naramoto, Hiroshi*; Lavrentiev, V.*; Narumi, Kazumasa; Maekawa, Masaki; Kawasuso, Atsuo; Yaita, Tsuyoshi; Baba, Yuji

Materials Transactions, 46(4), p.765 - 768, 2005/04

 Times Cited Count:17 Percentile:25.8(Materials Science, Multidisciplinary)

A systematic study of the atom-level mixtures between Co and C$$_{60}$$ has made possible to find a new C$$_{60}$$-based compound phase, Co$$_{x}$$C$$_{60}$$ (x$$leq$$5). It is confirmed with the EXAFS analysis and the positron annihilation study that the polymeric structure is developed three-dimensionally by bridging two C$$_{60}$$ molecules with the covalently bonded Co atom.

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:5.45(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:127 Percentile:3.67(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.

95 (Records 1-20 displayed on this page)