第一原理研究界面弛豫对InAs/GaSb超晶格界面结构、能带结构和光学性质的影响

通过广义梯度近似的第一原理全电子相对论计算, 研究了不同界面类型InAs/GaSb超晶格的界面结构、电子和光吸收特性. 由于四原子界面的复杂性和低对称性, 通过对InAs/GaSb超晶格进行电子总能量和应力最小化来确定弛豫界面的结构参数. 计算了InSb, GaAs型界面和非特殊界面(二者交替)超晶格的能带结构和光吸收谱, 考察了超晶格界面层原子发生弛豫的影响.为了证实能带结构的计算结果, 用局域密度近似和Hartree-Fock泛函的平面波方法进行了计算. 对不同界面类型InAs/GaSb超晶格的能带结构计算结果进行了比较, 发现界面Sb原子的化学键和离子性对InAs/GaSb超晶格的界面结构、 能带结构和光学特性起着至关重要的作用.     

Drop Size Dependence of the Contact Angle of Nanodroplets

The contact angle of nanosized non-polarized argon sessile droplets on a solid substrate is studied by using molecular dynamics simulations. It is found that the drop size dependence of the contact angle is sensitive to the interaction between the liquid molecules and solid molecules. The contact angle decreases with the decreasing drop size for larger interaction between the liquid molecules and the solid substrate, and vice versa. This observation is consistent with most of the previous theoretical and experimental results.     

Group Foliation Method and Functional Separation of Variables to Nonlinear Diffusion Equations

Generalized functional separation of variables to nonlinear diffusion equations is studied in terms of the extended group foliation method. A complete classification for the nonlinear diffusion equation with source term which admits functional separable solutions is presented.     

Thermal Properties of Materials Characterized by Scanning Electron-Acoustic Microscopy

A modified technique of scanning electron-acoustic microscopy is employed to determine thermal diffusivity of materials. Using the dependence of the electron-acoustic signal on modulation frequency of the electron beam, the thermal diffusivity of materials is characterized based on a simplified thermoelastic theory. The thermal diffusivities of several metals characterized by the modified scanning electron-acoustic microscopy are in good agreement with the referential values of the corresponding materials, which proves that the scanning electronacoustic microscopy can be used to characterize the thermal diffusivity of materials effectively. In addition, for micro-inhomogeneous materials, such as biological tissues, the macro-effective （average） thermal diffusivities are characterized by the technique.     

Wideband Antireflection Film Fabricated by Glancing Angle Deposition

Graded-index ZrO2 films has been fabricated on K9 glass by glancing angle deposition. Because the index mismatch at the interface has been reduced, the film results in wideband high-transmission antireflection. From 400nm to 1200nm, the film reflection is lower than 0.8% and the lowest value is 0.2% at 432nm.     

Luminescence and ESR Studies of CaS：Dy Phosphor

CaS phosphor activated with Dy ions is prepared by the solid-state diffusion method. The phosphor is characterized by x-ray powder diffraction, thermogravimetric analysis and photoiuminescence. Defect centres formed in CaS：Dy are studied using the technique of electron spin resonance. The thermoluminescence glow curve shows peaks at around 117℃ and 345℃. Irradiated CaS：Dy exhibits ESR lines due to defect centres. The thermal annealing behaviour of one of the defect centres appears to correlate with the TL peaks at 117℃ and 345℃. This centre is characterized by an isotropic g-value of 2.0035 and is assigned to an F^＋ centre.     

Dependence of stresses on grain orientations in BCC polycrystalline films on substrates

Most thin films have different thermal expansion coefficients from their substrates, thus thermal stresses will be introduced into the films when the temperature is changed during annealing and service. Calculations of these stresses for grains in various crystallographic orientations have been made for seven BCC transition metals Cr, Fe, Mo, Nb, Ta, V and W. Neglecting W, which is isotropic and the stresses are equiaxial and without grain orientation （hkl） dependence, the BCC metals may be grouped into two classes. In the first class （Cr, Mo, Nb and V）, the （100）-oriented grains have the largest stresses, while the stresses σ1 and σ2 in other （hkl）-oriented grains decrease linearly with the increase of the angle between （hkl） and （100）, and with σ1 〈 σ2 except in （100）- and （lll）-oriented grains. In the second class （Fe and Ta）, on the contrary, the （100）-oriented grains have the lowest stresses, and the stresses σ1 and σ2 in other （hkl）-oriented grains increase linearly with the increase of the angle between （hkl） and （100）, and with σ1 〉 σ2 except in （100）- and （111）-oriented grains.     

高温超导薄膜在微波双工器上的应用

本文采用全波电磁仿真方法设计、制作并测试了一种工作于C波段的星载高温超导微波双工器,采用的材料是在厚度为0.5mm介电常数为23.5的LaAlO3衬底上用磁控溅射法制备而成的双面氧化物高温超导薄膜YBCO.利用在微波范围内,高温超导薄膜的Q值比常规导体高1～3个数量级的特点,实现了器件的小型化和低插损.     

平面式一阶梯度计的设计和制备及其在无损检测上的应用

我们在10×10mm2的SrTiO3双晶基片上,设计并制备了YBCO双晶结dc-SQUID一阶平面式梯度计.其基线长度为5.5mm,该梯度计能够在无屏蔽环境下稳定的工作.在77K下,200Hz时,其磁通噪声为1×10-4Φ0/Hz,能够分辨的最小磁场梯度为94pT/m.我们将该器件作为磁传感器,可以利用涡流检测的原理对非磁金属进行无损检测.实验结果表明,可以很清楚地分辨出10mm以下的缺陷.同时,我们还研究了激励线圈的尺寸与空间分辨率的关系,结果表明若激励线圈足够大,则对于梯度计和缺陷而言感受到的是均匀磁场的激励,因此涡流的分布只与缺陷的形状有关,而空间分辨率取决于梯度计的基线长度和磁场分布.     

金纳米薄膜导电和导热性质的实验研究

由于尺寸效应和晶界效应的影响,纳米薄膜在导电和导热方面呈现出与体材料不同的性质.本文实验研究了不同厚度(20～54 nm)金薄膜在不同温度(100～340 K)的导电、导热性质.测量结果显示,薄膜的电导率和热导率比体材料小,洛伦兹数比体材料大,Wiedemann-Franz定律不再成立.随着厚度增加,薄膜的电导率,热导率和电阻温度系数都增加.薄膜热导率随温度变化趋势与体材料相反,随着温度升高而升高.电导率随温度变化趋势与体材料相同,随着温度升高而降低;但薄膜没有体材料对温度变化敏感,导致电阻温度系数下降.