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941.
Effects of an AlN passivation layer on the microstructure and electronic properties of AlGaN/GaN heterostructures were investigated by X-ray diffraction and Hall effect measurements. AlN passivation induced an additional compressive stress in an AlGaN barrier layer instead of an additional tensile stress induced by Si3N4 passivation. The change of strain after passivation contributes in a relatively small proportion to the variation of the carrier concentration in AlGaN/GaN heterostructures compared with the contribution from passivation of surface traps. The results from Hall effect measurements show that the AlN passivation layer has a better effect on passivation of deep levels than the Si3N4 film and also results in a remarkable increase in mobility of the two-dimensional electron gas. PACS 73.40.Kp; 71.55.Eq; 81.65.Rv; 81.05.Ea; 61.05.cp  相似文献   
942.
We present the number of dimer coverings N d (n) on the Sierpinski gasket SG d (n) at stage n with dimension d equal to two, three, four or five. When the number of vertices, denoted as v(n), of the Sierpinski gasket is an even number, N d (n) is the number of close-packed dimers. When the number of vertices is an odd number, no close-packed configurations are possible and we allow one of the outmost vertices uncovered. The entropy of absorption of diatomic molecules per site, defined as , is calculated to be ln (2)/3 exactly for SG 2. The numbers of dimers on the generalized Sierpinski gasket SG d,b (n) with d=2 and b=3,4,5 are also obtained exactly with entropies equal to ln (6)/7, ln (28)/12, ln (200)/18, respectively. The number of dimer coverings for SG 3 is given by an exact product expression, such that its entropy is given by an exact summation expression. The upper and lower bounds for the entropy are derived in terms of the results at a certain stage for SG d (n) with d=3,4,5. As the difference between these bounds converges quickly to zero as the calculated stage increases, the numerical value of with d=3,4,5 can be evaluated with more than a hundred significant figures accurate. This paper is written during the Lung-Chi Chen visit to PIMS, University of British Columbia. The author thanks the institute for the hospitality.  相似文献   
943.
俞金玲  陈涌海  赖云锋  程树英 《中国物理 B》2014,23(1):17806-017806
We theoretically study the influence of the spin–orbit coupling(SOC) on the in-plane optical anisotropy(IPOA) induced by in-plane uniaxial strain and interface asymmetry in(001) GaAs/AlGaAs quantum wells(QWs) with different well width. It is found that the SOC has more significant impact on the IPOA for the transition of the first valence subband of heavy hole to the first conduction band(1H1E) than that of 1L1E. The reason has been discussed. The IPOA of(001) InGaAs/InP QWs has been measured by reflectance difference spectroscopy, whose amplitude is about one order larger than that of GaAs/AlGaAs QWs. The anisotropic interface potential parameters of InGaAs/InP QWs are also determined. The influence of the SOC effect on the IPOA of InGaAs/InP QWs when the QWs are under tensile, compressive or zero biaxial strain are also investigated in theory. Our results demonstrate that the SOC has significant effect on the IPOA especially for semiconductor QWs with small well width, and therefore cannot be ignored.  相似文献   
944.
从杠杆的本质出发,提出杠杆是“放大”或“缩小”力的装置.按照从特殊到一般的顺序进行杠杆的教学,通过强化研究思路,全面介绍杠杆分类,从而使杠杆教学达到一个新的水平.  相似文献   
945.
A passively Q-switched tunable Yb-doped double-clad fiber laser is demonstrated with graphene epitaxially grown on SiC.The spectral tuning of the Q-switched fiber laser is implemented by rotating a quartz plate filter inside the cavity.The central wavelength of the fiber laser can be continuously tuned from 1038.54 to 1056.22 nm.The maximum pulse energy of 0.65 μJ is obtained at the pump power of 4.08 W,and the corresponding pulse duration and average output power are 1.60 μs and 35 mW,respectively.  相似文献   
946.
947.
High silica glass doped with Eu2+ ions was prepared as a scintillating material by impregnation of Eu ions into a porous silica glass followed by reduction sintering in CO atmosphere. A dominant emission band of the Eu2+ 5d–4f transition peaking around 430 nm was observed in the luminescence spectrum with the excitation peak around 280 nm and no emission from Eu3+ was present. Photoluminescence decay kinetics was governed by decay times of a few microseconds. The Eu2+‐doped high silica glass exhibited comparable energy resolution and slightly higher photoelectron yield with respect to the Bi4Ge3O12 crystal in the pulse height spectra for X‐ray photon energies within 22–60 keV. Furthermore, a factor of 1.2 higher radioluminescence intensity was observed as well. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   
948.
Tian J  Yao Y  Jun Xiao J  Xu X  Chen D 《Optics letters》2011,36(8):1509-1511
We propose a fiber laser that can operate with passive mode-locking pulse output, continuous single-wavelength emission, and continuous multiwavelength emission. It consists of a nonlinear optical loop mirror (NOLM) in a linear cavity. The NOLM is used to induce different kinds of intensity-dependent feedback, which determine the operation mode of the laser. We have experimentally demonstrated that the fiber laser can easily be switched between the operation modes. The results may find useful applications in optical communication and fiber sensing.  相似文献   
949.
We study mesoscopic spin Hall effect on the surface of a topological insulator with a step-function potential by using the McMillan method commonly used in the study of superconductor junctions. In the ballistic transport regime, we predict a giant spin polarization induced by a transverse electric current with parameter suitable to the topological insulator thin film Bi(2)Se(3). The spin polarization oscillates across the potential boundary with no confinement due to the Klein paradox, and should be observable in a spin resolved scanning tunneling microscope.  相似文献   
950.
We demonstrate a 300?μm long silicon photonic crystal (PC) slot waveguide device for on-chip near-infrared absorption spectroscopy, based on the Beer-Lambert law for the detection of methane gas. The device combines slow light in a PC waveguide with high electric field intensity in a low-index 90?nm wide slot, which effectively increases the optical absorption path length. A methane concentration of 100?ppm (parts per million) in nitrogen was measured.  相似文献   
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