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排序方式: 共有178条查询结果,搜索用时 31 毫秒
131.
A new fit to the long-range angular correlation of annihilation radiation data of the sum of a parabola, so-called Ferrell function, and a Gaussian for noble and d-transition metals is presented. The three functions are considered to describe the positron annihilation with three different electron groups: nearly free, d-like and rare-gas core electrons, respectively. 相似文献
132.
T. E. Jackman G. C. Aers M. W. Denhoff P. J. Schultz 《Applied Physics A: Materials Science & Processing》1989,49(3):335-339
Silicon epilayers grown by molecular beam epitaxy and doped in-situ using low-energy implantation were examined using a variable-energy positron beam. The samples had been previously characterized using electrical measurements, ion channeling, SIMS, and electron microscopy. The positron results show that defects have been created in layers grown at 460°C and in the highly doped layers grown at 700°C. The assignment of defect structures is difficult at present, but is consistent with the formation of As clusters or Asvacancy complexes. 相似文献
133.
C. Corbel P. Bernède H. Pascard F. Rullier-Albenque R. Korman J. F. Marucco 《Applied Physics A: Materials Science & Processing》1989,48(4):335-341
We report positron lifetime measurements in sintered superconducting YBa2Cu3O7–x
and GdBa2Cu3O7–x
oxides. It is shown that the thermal behaviour of the positron lifetime spectra strongly depends on the preparation of the ceramics. A lifetime of 190±3 ps is attributed to oxygen deficient regions. Two lifetimes of 251±7 ps and 225 ±5 ps are attributed to a cation vacancy presenting a temperature dependent atomic arrangement. The lifetime transition (251225ps) occurs during decreases in temperature across the resistivity superconducting transition. This lifetime change indicates that the volume of the cation vacancy decreases in the superconducting state. 相似文献
134.
R. M. de la Cruz R. Pareja A. Segura P. Moser A. Chevy 《Applied Physics A: Materials Science & Processing》1992,54(2):147-151
The positron annihilation characteristics of the layered semiconductor InSe have been investigated. No evidence for low temperature positron trapping is found in as-grown and heavily deformed InSe. The temperature dependence of the S-parameter in these sample exhibits an increase rate in good agreement with the linear expansion coefficient along the c-axis. The positron lifetime spectra of electron-irradiated 0.01% Sn-doped InSe show a long-lifetime component of 336 ps which is tentatively attributed to positrons trapped at isolated In vacancies. Isochronal annealing experiments performed on these samples show that the recovery of the positron lifetime measured at 77K is accomplished in two stages. The first, starting after annealing at 150K, could be induced by the formation of complexes (VIn-SnIn). The second stage, observed at temperatures T375K, is attributed to the dissociation of these complexes and subsequent annealing of the In vacancies. 相似文献
135.
Hitoshi Sato Anurag Tyagi Hong Zhong Natalie Fellows Roy B. Chung Makoto Saito Kenji Fujito James S. Speck Steven P. DenBaars Shuji Nakamura 《固体物理学:研究快报》2007,1(4):162-164
We demonstrate a high power green InGaN/GaN multiple‐quantum‐well (MQW) light emitting diode (LED) with a peak emission wavelength of 516 nm grown on low extended defect density semipolar (11 2) bulk GaN substrate by metal organic chemical vapor deposition. The output power and external quantum efficiency (EQE) at drive currents of 20 and 100 mA under direct current (DC) operation were 5.0 mW, 10.5% and 15.6 mW, 6.3%, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
136.
U. Lommatzsch E.H. Wahl D. Aderhold T.G. Owano C.H. Kruger R.N. Zare 《Applied Physics A: Materials Science & Processing》2001,73(1):27-33
A mixture of H2 and CH4 is passed over a hot-wire tungsten filament in a diamond thin film chemical vapor deposition reactor. The resulting CH radicals
are measured in absorption using cavity ring-down spectroscopy (CRDS). The concentration of the CH radicals increases as the
filament is approached. The rotational temperature measurements indicate a large temperature discontinuity between the filament
and the CH in the gas phase. The pathways for CH production were investigated by replacing H2 by D2 in the feed gas mixture, which resulted in the exclusive production of CD. From this observation it is concluded that rapid
H/D isotope exchange dominates in the gas phase. Nonperiodic temporal oscillations in the CH concentration are observed when
a rhenium filament is used in place of a tungsten filament. The oscillations are attributed to the nonperiodic changes in
the amount of carbon at the filament surface.
Received: 21 August 2000 / Accepted: 23 August 2000 / Published online: 23 May 2001 相似文献
137.
J. Gebauer F. Rudolf A. Polity R. Krause-Rehberg J. Martin P. Becker 《Applied Physics A: Materials Science & Processing》1999,68(4):411-416
14 cm-3 in FZ-Si was obtained.
Received: 2 June 1998 / Accepted: 20 November 1998 / Published online: 24 February 1999 相似文献
138.
We report on the frequency doubling of Q-switchedNd:YAG and Nd:YAlO3 lasers emitting at 946 and 930 nm, respectively (4F3/2 to 4I9/2 transition). The neodymium-doped laser host crystals were excited with a flashlamp-pumped Cr:LiSAF laser operating in a free-running
mode. Blue-light pulses were obtained at both 473 nm (9 mJ, 25 ns FWHM) and 465 nm (4.4 mJ, 35 ns FWHM) by using a potassium
niobate crystal as an extra-cavity frequency doubler. The second-harmonic generation conversion efficiencies reached 53% and
31%, respectively.
Received: 23 June 1999 / Revised version: 8 August 1999 / Published online: 3 November 1999 相似文献
139.
Zhiqiang Yang Yichuan Chen Jing Li Chen Lu Junfang Zhao Mengtao Sun 《Frontiers of Physics》2023,18(3):33303
The first successful synthesis of fully fused and fully conjugated Möbius carbon nanobelts (CNBs) has attracted considerable attention. However, theoretical calculations based on such π-conjugated Möbius CNB are still insufficient. Herein, we theoretically investigated molecular spectroscopy of Möbius CNBs without and with n-butoxy groups via visualization methods. The results show that the presence of n-butoxy groups can significantly affect Möbius CNBs’ optical performance, changing electron-hole coherence and enhancing two-photon absorption cross-sections. Our work provides a deeper understanding of photophysical mechanisms of Möbius CNBs in one- and two-photon absorption and reveals possible applications on optoelectronic devices. 相似文献
140.
Kwang‐Choong Kim Mathew C. Schmidt Hitoshi Sato Feng Wu Natalie Fellows Makoto Saito Kenji Fujito James S. Speck Shuji Nakamura Steven P. DenBaars 《固体物理学:研究快报》2007,1(3):125-127
Improved nonpolar m ‐plane light emitting diodes (LEDs) with a thick InGaN multi‐quantum‐well (MQW) structure have been fabricated on low extended defect bulk m ‐plane GaN substrates using metal organic chemical vapor deposition (MOCVD). The peak wavelength of the electroluminescence emission from the packaged LEDs was 402 nm, which is in the blue‐violet region. The output power and EQE were 28 mW and 45.4%, respectively, at a pulsed driving current of 20 mA. With increasing current, the output power increased linearly, and fairly flat EQE was observed with increasing drive current. At 200 mA, the power and EQE were 250 mW and 41%, respectively. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献