Influence of thermal annealing duration of buffer layer on the crystalline quality of In0.82Ga0.18As grown on InP substrate by LP-MOCVD

In_0.82Ga_0.18As epilayers were grown on InP substrates using a two-step growth technique by LP-MOCVD. A homogeneous low-temperature (450 °C) In_0.82Ga_0.18As buffer layer was introduced to improve the crystalline quality of epilayers. The influence of low-temperature buffer layer deposition condition, such as thermal annealing duration, on the crystalline quality of the In_0.82Ga_0.18As epilayer was investigated. Double-crystal X-ray diffraction measurement, Hall measurement, and Raman scattering spectrum were used to evaluate the In_0.82Ga_0.18As epilayers. Atomic force microscope was used to study the surface morphology. It is found that the In_0.82Ga_0.18As epilayer, with buffer layer thermal annealing for 5 min, exhibits the best crystalline quality. The change of the surface morphology of the buffer layer after thermal annealing treatment was suggested to explain the phenomenon.     

Preparation and properties of SnS film grown by two-stage process

SnS films have been prepared by a novel two-stage process. It involved sputtering of Sn film on glass substrate and sulfurization of the thin metallic tin precursor layers in a vacuum furnace. The X-ray diffraction results showed that the SnS layers had orthorhombic structure and (0 4 0) preferential growth is more and more obvious with the increase of sulfurization time. The SnS film obtained by this work shows high optical absorption efficiency, and the film has a direct optical band gap of about 1.3 eV. The films show p-type conductivity and the resistivity of SnS film decreased obviously under illumination.     

Charge-response of magnetization in nanoporous Pd-Ni alloys

This work reports isothermal reversible variation of magnetization in nanoporous Pd-Ni alloys subjected to continuous charging and discharging of the sample in aprotic electrolyte medium. Polarizing metal surface with excess charge also finds strain in the nanoporous structure using the sample as working electrode. Therefore, it is proposed that pressure induced by strain is the key parameter for the observed reversible magnetization in the transition metal alloys.     

Microstructure, optical and static recording properties of AgOx film, and near-field simulation of sub-wavelength aperture based on the AgOx marks’ formation

Structures, spectra and surface topographies of as-deposited and annealed AgO_x films have been investigated by an X-ray diffractometer, a spectrophotometer and an atomic force microscopy (AFM). X-ray diffraction and spectrum results show that the as-deposited AgO_x films with high oxygen ratios (x≥0.5) are in amorphous states and Ag crystalline particles will separate out after annealed. AFM results show that the film surface will become much rougher and film thickness will increase greatly after annealed due to the decomposition of AgO_x with release of oxygen. Static recording results show that two microstructures of the recording marks can be produced: one is the bubble mark at a low recording power and the other is the rupture bubble with an ablated aperture (hole) in the center at a high recording power. Based on the formation of rupture bubble marks, the near-field optical distribution of a focused Gaussian laser beam through a sub-wavelength aperture (200 nm in diameter) has been simulated using finite-difference-time-domain (FDTD) method. Results show that the spot size can be greatly squeezed with still highly transmitted intensity, which may lead to the super-resolution readout.     

Nonlinear spectral-like schemes for hybrid schemes

In spectral-like resolution-WENO hybrid schemes,if the switch function takes more grid points as discontinuity points,the WENO scheme is often turned on,and the numerical solutions may be too dissipative.Conversely,if the switch function takes less grid points as discontinuity points,the hybrid schemes usually are found to produce oscillatory solutions or just to be unstable.Even if the switch function takes less grid points as discontinuity points,the final hybrid scheme is inclined to be more stable,provided the spectral-like resolution scheme in the hybrid scheme has moderate shock-capturing capability.Following this idea,we propose nonlinear spectral-like schemes named weighted group velocity control(WGVC)schemes.These schemes show not only high-resolution for short waves but also moderate shock capturing capability.Then a new class of hybrid schemes is designed in which the WGVC scheme is used in smooth regions and the WENO scheme is used to capture discontinuities.These hybrid schemes show good resolution for small-scales structures and fine shock-capturing capabilities while the switch function takes less grid points as discontinuity points.The seven-order WGVC-WENO scheme has also been applied successfully to the direct numerical simulation of oblique shock wave-turbulent boundary layer interaction.     

Electrical and dielectric properties of Al/p-Si and Al/perylene/p-Si type diodes in a wide frequency range

The perylene(C20H12) layer effect on the electrical and dielectric properties of Al/p-Si(MS) and Al/perylene/p-Si(MPS) diodes have been investigated and compared in the frequency range of 0.7 kHz–2 MHz. Experimental results show that C–V characteristics give an anomalous peak for two structures at low frequencies due to interface states(Nss) and series resistance(Rs). The increases in C and G/ω at low frequencies confirm that the charges at interface can easily follow an ac signal and yield excess capacitance and conductance. The frequency-dependent dielectric constant(ε) and dielectric loss(ε) are subtracted using C and G/ω data at 1.5 V. The ε and ε values are found to be strongly dependent on frequency and voltage, and their large values at low frequencies can be attributed to the excess polarization coming from charges at traps. Plots of ln(σac)–ln(ω) for two structures have two linear regions, with slopes of 0.369 and 1.166 for MS, and of 0.077 and 1.061 for MPS, respectively. From the C 2–V characteristics, the doping acceptor atom concentration(NA) and barrier height(ΦB) for Schottky barrier diodes(SBDs) of MS and MPS types are also obtained to be 1.484 × 1015 and 1.303 × 1015cm 3, and 1.10 and 1.13 eV, respectively.     

Nonlinear interaction mechanisms of disturbances in supersonic flat-plate boundary layers

Due to the complexity of compressible flows, nonlinear hydrodynamic stability theories in supersonic boundary layers are not sufficient. In order to reveal the nonlinear interaction mechanisms of the rapidly amplified 3-D disturbances in supersonic boundary layers at high Mach numbers, the nonlinear evolutions of different disturbances in flat-plate boundary layers at Mach number 4.5, 6 and 8 are analyzed by numerical simulations. It can be concluded that the 3-D disturbances are amplified rapidly when the amplitude of the 2-D disturbance reaches a certain level. The most rapidly amplified 3-D disturbances are Klebanoff type (K-type) disturbances which have the same frequency as the 2-D disturbance. Among these K-type 3-D disturbances, the disturbances located at the junction of upper branch and lower branch of the neutral curve are amplified higher. Through analyzing the relationship between the amplification rate and the spanwise wavenumber of the 3-D disturbances at different evolution stages, the mechanism of the spanwise wavenumber selectivity of K-type 3-D disturbances in the presence of a finite amplitude 2-D disturbance is explained.     

塑料闪烁光纤阵列成像探测器在高能X射线辐照下的串扰分析

采用蒙特卡罗方法对闪烁光纤阵列探测器在高能X射线入射下的串扰进行了模拟研究,并且分析比较了加铅层对串扰的影响.研究中采用对表征成像系统空间分辨率参量——调制传递函数进行模拟分析和比较,得到在光纤阵列之间加入不同铅层厚度后对系统调制传递函数参量曲线的影响.研究结果表明:在高能射线下,采用闪烁光纤阵列作为成像探测器存在严重的次级粒子相互串扰的现象,而在阵列之间加入铅介质能够减少这种效应;但另一方面,若所加铅层太厚又会导致成像探测器像素过大而使得空间分辨率下降.通过模拟计算得出:只要在阵列之间加入适当厚度的铅介质,既可以有效抑止阵列之间次级粒子的串扰,同时又能提高闪烁光纤阵列探测器系统的空间分辨率.     

MRTD算法在集成平面光波导组件分析中的应用

将基于Daubechies紧支集尺度函数的时域多分辨分析（MRTD）算法用于集成平面光波导组件的时域分析中,实现了MRTD算法的各向异性理想匹配层（APML）吸收边界条件,并对平行介质带定向耦合器进行了数值模拟和验证,所得结果与解析解非常一致.与传统的FDTD算法相比,MRTD算法在不牺牲计算精度的前提下能够大大节省计算资源.     

实验"不良导体导热系数的测量"计算方法的改进

本文在考虑了格拉晓夫准则、努塞尔准则及雷利准则的情况下,对实验“不良导体导热系数的测量”的计算方法做了改进.