轴流式射频PCVD沉积质量分布的动力学分析

在用静电探针诊断了轴流式射频等离子体激活化学汽相沉积(PCVD)反应器中等离子体电子温度、电子密度轴向分布的基础上,提出与主要工艺参数相联系的二元流体动力学模型。以等离子体参量的轴向分布和变化规律为中介量,从动力学的角度分析主要工艺参数影响PCVD沉积质量分布的规律。将模型用于沉积SnO₂薄膜的过程,理论计算与实验结果符合较好。 关键词：     

柠檬酸根对纳米Fe3O4颗粒的生长及性能的影响

现代诊断学的发展使得超小超顺磁性的Fe₃O₄粒子在医学领域具有重要应用价值。实验中利用某些羧酸盐对铁氧化物晶粒成长的抑制作用，在共沉淀法中引入柠檬酸根，制备出平均粒径小于5 nm的Fe₃O₄纳米分散体系。研究了不同柠檬酸根浓度对生成粒子的大小、结晶和表面吸附情况的影响。对Fe₃O₄颗粒在不同条件下的磁性与胶体稳定性进行了讨论。     

准一维有机铁磁体的磁性机理研究

对准一维有机铁磁体ｐｏｌｙ－ＢＩＰＯ体系的磁性机理进行了研究。详细考虑了该体系中的电子跳跃、电子关联及派尔斯不稳定性，自洽地计算了其能带结构和自旋密度分布，并数值地研究了各因素对系统特性的影响。结果发现该体系基态为稳定的铁磁态． 关键词：     

Block Entanglement in the Single-Hole Hubbard Model

We investigate the distribution of the entanglement of the one-dimensional single-hole Hubbard model （HM） and study the relationship between the entanglement and quantum phase transition in the model. The von Neumann entropy of a block with neighbouring spins L for a single-hole HM is calculated using the densitymatrix renormalization group. The distributions of the entanglement entropy in the ground state, as a function of block length, show a dramatic effect, i.e. effectively decoupling with the centres, no matter how the Coulomb interaction u 〉0 or u 〈0. Contrarily, for the Coulomb interaction u = 0 or close to zero, the entanglement entropy in the single-hole model reaches a saturation value for a certain block size. For a fixed size L = 40, the ground state entanglement entropy measure, as a function of u1 shows a peak corresponding to the critical quantum phase transition.     

First-principles investigations on the mechanical,thermal,electronic,and optical properties of the defect perovskites Cs_2SnX_6(X= Cl,Br, I)

The mechanical properties, thermal properties, electronic structures, and optical properties of the defect perovskites Cs_2SnX_6(X = Cl, Br, I) were investigated by first-principles calculation using PBE and HSE06 hybrid functional. The optic band gaps based on HSE06 are 3.83 eV for Cs_2SnCl_6, 2.36 eV for Cs_2SnBr_6, and 0.92 eV for Cs_2SnI_6, which agree with the experimental results. The Cs_2SnCl_6, Cs_2SnBr_6, and Cs_2SnI_6 are mechanically stable and they are all anisotropic and ductile in nature. Electronic structures calculations show that the conduction band consists mainly of hybridization between the halogen p orbitals and Sn 5s orbitals, whereas the valence band is composed of the halogen p orbitals. Optic properties indicate that these three compounds exhibit good optical absorption in the ultraviolet region, and the absorption spectra red shift with the increase in the number of halogen atoms. The defect perovskites are good candidates for probing the lead-free and high power conversion efficiency of solar cells.     

由单负材料组成的一维对称型光子晶体中的隧穿模

由电单负材料A和磁单负材料B构成了一维对称型光子晶体,数值计算表明其带隙中出现了一隧穿模. 材料层数增加,隧穿模宽度急剧变窄,而其位置不变.隧穿模的位置和宽度对入射角的变化都不太敏感. 材料的几何厚度减小,隧穿模的位置蓝移,而其宽度不变. μ_A, ε_B增加,隧穿模的位置红移,宽度减小. 利用隧穿模的以上特性可以实现对电磁波传播的动态调控.     

Kadomtsev-Petviashvili方程的精确解

齐次平衡法是把非线性偏微分方程转换成带约束条件的线性偏微分方程的一种很好的方法 .本文在齐次平衡法的基础上具体讨论了KP方程的精确解 ,包括孤波解 ,一般的行波解 ,有理函数解和一种新类型的解 .     

美国大学的物理实验教学及其管理

一、引言自1980年至1984年,我们两人作为访问学者和研究人员(Research Associate),在美国明尼苏达大学物理系,分别进修、工作两年多时间。明尼苏达大学是美国前二十个名牌大学之一。全校有5万多名学生,18个学院,250个专业。有来自105个国家的留学生,全校有4000多名教授,其中不少是世界上有名望的学者。仅工学院380名教授中,就有7名科学院院士,13名工程科学院院士。在这段时间内,我们除参加各自的研究课题     

Copper Nanobelt Reorientation by Molecular Dynamics Simulation

Atomic simulations using embedded atom method （EAM） are performed for Cu （100） nanobelts to study the structural and mechanical behaviour. Cu （100） nanobelts are along[001] taken as the z-axis and have a rectangular cross section in the x - y plane, with [100] and [010] taken as x and y axes. The periodic boundary is used along the z-axis to simulate an infinitely long nanobelt, and other surfaces are free. The simulations are carried out under the mechanical loading with an elongation strain rate of 8.0×10^8 s^-1 along the z-axis. The results show that the nanobelt undergoes a transition from the initial structure with a （100） axis and {100} lateral surfaces to a new structure with the （112） as the z-axis and the lateral surfaces are {111} and {110} respectively, instead of the original {100} surfaces. The mechanism of the structural transition is ascribed to the dislocation propagation through the nanobelt under the external stresses.     

Nonlinear current－voltage characteristics of sintered tungsten－vanadium oxide

We have studied the densification behaviour, microstructure and electrical properties of WO_3 ceramics with V_2O_5 as the additive ranging from 0.5 to 15mol%. Scanning electron microscopic photos indicated that the grain size of WO_3－V_2O_5 specimens is smaller than that of pure WO_3. The addition of V_2O_5 to WO_3 showed a tendency to enhance the densification rate and to restrict the grain growth. Electrical properties of all specimens were measured for different electrodes at different temperatures. The formation of the grain boundary barrier layer was confirmed by the non-ohmic I－V behaviour. The nonlinear coefficient was obtained at the current density J=0.01, 0.1 and 1mA/cm^2 for a series of WO_3－V_2O_5 samples. The V0.5mol% specimen showed an abnormal phenomenon that the nonlinear characteristics appeared at 350℃ and disappeared at lower and higher temperatures. This implies that it could be applied as a high-temperature varistor. The double Schottky barrier model was adopted to explain the phenomena for the WO_3-V_2O_5 varistors.