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111.
Defects in Si-Rich SiO2 Films Prepared by Radio-Frequency Magnetron Co-sputtering Using Variable Energy Positron Annihilation Spectroscopy
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Si-rich SiO2 films prepared by rf magnetron co-sputtering method are studied by slow positron beams. The nega- tively charge point defects (probably Pb centres or peroxy radicals) at the silicon nanocluster (nc-Si)/SiO2 interface are observed by Doppler broadening spectra. Coincidence Doppler-broadening spectra show that positrons have a higher annihilation probability with core electrons nearby oxygen atoms than silicon atoms. The formation of N-related bonds may be the reason for the prevention of the migration reaction of Si and 0 atoms, hence nc-Si formation is inhibited by annealing in nitrogen compared to in vacuum. 相似文献
112.
The effect of real-time information on the traffic flows of the crossing roads is studied by simulations based on a cellular automaton model. At the intersection, drivers have to enter a road of a shorter trip-time, by making a turn if necessary, as indicated on the information board. Dynamics of the traffic are expressed as a return map in the density-flow space. The traffic flow is classified into six phases, as a function of the car density. It is found that such a behavior of drivers induces too much concentration of cars on one road and, as a result, causes oscillation of the flow and the density of cars on both roads. The oscillation usually results in a reduced total flow, except for the cases of high car density. 相似文献
113.
We report on the observation of quasi-phase matched collinear second harmonic generation (SHG) at 20 wavelengths in a two-dimensional nonlinear photonic quasi-crystal with decagonal lattice. We show that at some wavelengths the second harmonics are generated via standard quasi-phase matching, namely a reciprocal vector exists that equals the phase-mismatch vector, while at others the SHG is as a result of the projection-based quasi-phase matching in which the momentum conservation is satisfied up to a projection of a reciprocal vector onto the direction of propagation. In spite of different generation mechanisms, the reciprocal vectors (or their projections) involved in the collinear QPM SHG can be described by a generalized equation. 相似文献
114.
K. Hirata Y. Kobayashi S. Hishita Y. Ujihira 《Applied Physics A: Materials Science & Processing》1997,64(5):491-495
+ and O+ ions was exposed to positron beams to measure the positron annihilation Doppler broadening as a function of the positron
energy. As in the previous case of O+-irradiated semicrystalline PEEK, the annihilation lines recorded at relatively low positron energies became broader with
increasing irradiation dose. The thickness of the damaged layer estimated from the positron data was compared with the mean
depth of the implanted ions calculated by the TRIM code. For the Au+-irradiated samples, some discrepancy was observed between the two quantities.
Received: 6 March 1996/Accepted: 19 November 1996 相似文献
115.
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
116.
Nonlinear processes in magnetized plasma are very much important for the proper understanding of many space and astrophysical events. One of the most important type of study has been done in the domain of Alfven waves. Here we show that a Galerkin type approximation of the DNLS (Derivative Nonlinear Schrödinger) equation describing such wave propagation leads to a new type of nonlinear dynamical systems, very much rich in chaotic properties. Starting with the detailed analysis of fixed points and stability zones we make an in depth study of the unstable periodic orbits, which span the whole attractor. Next the birth of a Hopf bifurcation is identified and normal form, limit cycle analyzed. In the course of our study the detailed structure of the attractor is analyzed. A possibility of internal crisis is also indicated. These results will help in the choice of the plasma parameters for the actual physical situation. 相似文献
117.
Contamination-tolerant adhesives are of ever increasing importance in industrial applications. The possible failure mechanisms of adhesive bonds in these adhesives are however still poorly understood. Results of a series of investigations with our pulsed low energy positron beam system (PLEPS) in an epoxy-based contamination-tolerant adhesive are presented. 相似文献
118.
Simulations of the positron response to the mechanical deformation of Ni3Al nanowires are performed on modelled samples obtained using molecular dynamics. Particular attention is paid to the evolution of the various open volume defects and their interaction during deformation. Positron simulations are done in conjunction with a general, geometrical analysis of open volumes in the studied samples, which brings complementary information to the positron response results. 相似文献
119.
In spite of previous extensive studies, the helium behavior in metals still remains an issue in microelectronics as well as in nuclear technology. A gold-silver solid solution (Au60Ag40: synthetic gold-rich electrum) was chosen as a relevant model to study helium irradiation of heavy metals. After helium-3 ion implantation at an energy ranging from 4.2 to 5.6 MeV, nuclear reaction analysis (NRA) based on the 3He(d,p)4He reaction, was performed in order to study the thermal diffusion of helium atoms. At room temperature, NRA data reveal that a single Gaussian can fit the He-distribution, which remains unchanged after annealing at temperatures below 0.45 of the melting point. Slow positron implantation spectroscopy, used to monitor the fluence dependence of induced defects unveils a positron saturation trapping, which occurs for He contents of the order of 50-100 appm, whereas concentrations larger than 500 appm seem to favor an increase in the S-parameter of Doppler broadening. Moreover, at high temperature, NRA results clearly show that helium long range diffusion occurs, though, without following a simple Fick law. 相似文献
120.
Positron annihilation lifetime (PAL) and Doppler broadening (DB) techniques have been performed to identify structural defects of the bismuth based pyrochlore systems with generic formula (Bi1.5Zn0.5)(Zn0.5−x/3TixNb1.5−2x/3)O7 (x = 0, 0.25, 0.5,1.0, 1.5). We found that all studied compounds contain substantial amount of the lattice vacancy defects, the variation of the annihilation lifetime suggests that the defects structure undergoes significant changes. The complex defects could be produced with increasing content of Ti, resulting in a drop in the intensity I2 in the Ti-rich sample. At 1 MHz their dielectric constant (?′) varies from 150 for Ti-poor system to 210 for Ti-rich system and loss tangent (tan δ) remains rather low level. The high dielectric constant response of the BZTN ceramics is attributed to loosening state of cations located in the center of octahedral, so favor off-center displacement. The occurrence of complex defects help to enhance the dielectric constant. 相似文献