Submonolayer Au on Si(111) phase diagram

Based on a review of the current literature, a surface phase diagram is proposed for the submonolayer Au on Si(111) system. Kinetic considerations are reviewed and key surface phase diagram features such as the Θ < 0.4 ML metastable structure and the high temperature to Si(111)-(1 × 1)Au second order phase transition are discussed. Experiments to verify certain portions of the phase diagram are proposed.     

限流沿对撞壁射流近壁区混合过程影响的实验研究(一)

本文研究了射流气体撞壁后在放有条形障碍物(以下称之为限流沿)的壁面上的发展过程．实验发现：在限流沿高度合适的情况下，射流气体与限流沿相撞后会脱离壁面形成空间流动。其中，限流沿高度、射流入射角度是决定射流气体撞击限流沿后的发展过程的重要参数，限流沿的存在成功地防止了近壁处的浓混合气层的形成．     

数字波束形成算法仿真实现

从讨论波束形成方法在声系统中的主要作用和主要形成过程入手，介绍几种具体实现波束形成的算法。主要讨论一种能够降低硬件要求的波束形成算法——正交波束形成算法。此种方法不但适用于声系统，对于其他检测系统也有一定的实际意义。给出几种主要波束形成算法的Matlab仿真实现程序，将按照此类方法仿真所得到的波束形成指向性图与理论指向性图比较，两者非常类似。     

Mg掺杂PST薄膜的溶胶-凝胶法制备及晶相形成研究

利用溶胶-凝胶法成功制备了Mg掺杂Pb_0.4Sr_0.6Mg_xTi< sub>1-xO_3-x薄膜，利用x射线衍射仪对薄膜的物相和结构进行了分析， 用扫描电子显微镜对薄膜的形貌和断面等进行了观察.研究结果表明，薄膜以立方钙钛矿为 晶相，薄膜中晶相以团聚状颗粒存在，晶相含量受热处理条件和Mg的掺杂量所控制.Mg掺杂 对Pb_0.4Sr_0.6Mg_xTi_1-xO_3-x 薄膜晶相含量的影响与钙钛矿中的氧空位缺陷相关.在一定的掺杂范围内，由掺杂引起晶相 的晶格畸变较小时，体系掺Mg平衡了晶体内本征氧空位引入的电荷不平衡，使晶相更为稳定 ，析晶能力提高，晶体形成量随掺杂浓度的提高而提高.当掺杂浓度达到一定量时， 随着Mg 掺杂浓度增加，一方面使形成晶体时杂质浓度增加造成参与形成晶相的组成含量下降，另一 方面使进入钙钛矿结构的Mg增加，氧空位大量增加使畸变程度提高，形成的晶相不稳定，析 晶能力下降，晶体含量随掺杂Mg浓度的增加而不增反降.在相同条件下制备的Pb_{0.4Sr0.6MgxTi1-xO3-x薄膜中Mg掺量约为 x=0.01时，得到的钙钛矿相含量最高，本征氧缺陷所带入的正电荷和Mg引入时带入的负电荷 间达到平衡.此外，Mg的掺入还影响到析晶与热处理过程之间的关系.在高Mg掺量范围，Mg含 量越高，形成的晶相越不稳定，热处理时间越长，使热处理过程中分解的晶相量越多，随Mg 掺量越高和热处理时间越长，薄膜中晶相含量越低. 关键词： 溶胶-凝胶法 PST薄膜 Mg掺杂 晶相形成}     

Phase formation and magnetic properties of Nd2Fe14B-type Nd16Co76B8−xCx alloys and their hydrides

An attempt is made to synthesize Nd₂Co₁₄C compound by mechanical alloying Nd₁₆Co₇₆B_8−xC_x (0x8) alloys and subsequent annealing. Phase formation and magnetic properties of Nd₂Fe₁₄B-type Nd₁₆Co₇₆B_8−xC_x alloys and their hydrides are investigated. The Nd₂Co₁₄(B,C) phase with Nd₂Fe₁₄B-type structure is formed for Nd₁₆Co₇₆B_8−xC_x (0x7) alloys, while NdCo₇C_δ phase with TbCu₇-type structure is observed in Nd₁₆Co₇₆C₈ alloy. The lattice parameter c of the Nd₂Co₁₄(B,C) phase decreases with increasing the carbon content. A limit volume of the unit cell to form the Nd₂Fe₁₄B-type structure is estimated to be 0.870 nm³. The spin-reorientation temperature T_SR increases with increasing the carbon content, due to an enhancement of magnetocrystalline anisotropy caused by carbon substitution for boron. After hydrogenation, the lattice expansion is observed for Nd₁₆Co₇₆B_8−xC_x (0x7) alloys. The spin-reorientation temperature of Nd₁₆Co₇₆B_8−xC_xH_y (0x7) is much lower than that of the host alloys. Some structural and magnetic properties of hypothetic Nd₂Co₁₄C and Nd₂Co₁₄CH_y compounds are estimated by extrapolation.     

Evidence for diffusion-limited kinetics during electromigration-induced step bunching on Si(1 1 1)

We have measured how the initial terrace width l₀ on vicinal Si(1 1 1) surfaces influences the rate of step bunching and the minimum terrace width within a bunch when direct-current heated at 940-1290 °C. A comparison of this data with analytic solutions and numerical simulations of the conventional “sharp-step” model give strong evidence that the kinetic length d is relatively small (d < ∼20 nm) in both temperature regime I (∼850-950 °C) and regime III (∼1200-1300 °C), in which step-down current is required for step bunching. This indicates that surface mass transport is diffusion-limited in both regimes I and III when l₀ > 20 nm, and hence that the adatom attachment- and terrace diffusion-hopping rates are of comparable magnitude. We also observe similar scaling with initial terrace width in temperature regime II (∼1040-1190 °C), in which step-up current is required for bunching, suggesting a similar step bunching mechanism in all three temperature regimes.     

Orientation and structure of triple step staircase on vicinal Si(1 1 1) surfaces

The vicinal Si(1 1 1) surface, inclined towards the direction, was investigated by scanning tunnelling microscopy and spot profile analysing low energy electron diffraction. It has been established that the surface, consisting of regularly spaced triple steps and (1 1 1) terraces with a width equal to that of a single unit cell of the Si(1 1 1)-7 × 7 surface structure, has the (7 7 10) orientation. An atomic model of the triple step is proposed.     

铷原子热蒸气中强非线性效应产生激光模式图样的实验研究

研究了具有高斯横向分布的连续激光束单次通过铷原子蒸气后,在近共振附近铷原子蒸气中,由强的非线性克尔效应导致激光分裂成细丝的现象,并且这些细丝的衍射图样在远场通过相干叠加,可以形成具有规则结构的斑图模式.实验上研究了输入光功率,铷泡温度和抽运激光频率相对于⁸⁵Rb原子D₂线的不同失谐位置等因素对斑图模式的影响.由于铷原子的超精细能级结构,在铷原子蒸气中同时存在与三阶非线性效应相关的四波混频现象,通过扫描探测光的频率同时观察到具有斯托克斯和反斯托克斯光子的拉曼增益现象. 关键词： 铷原子蒸气 克尔效应 自聚焦 斑图     

Cluster synchronization in complex network of coupled chaotic circuits: An experimental study

By a small-size complex network of coupled chaotic Hindmarsh-Rose circuits, we study experimentally the stability of network synchronization to the removal of shortcut links. It is shown that the removal of a single shortcut link may destroy either completely or partially the network synchronization. Interestingly, when the network is partially desynchronized, it is found that the oscillators can be organized into different groups, with oscillators within each group being highly synchronized but are not for oscillators from different groups, showing the intriguing phenomenon of cluster synchronization. The experimental results are analyzed by the method of eigenvalue analysis, which implies that the formation of cluster synchronization is crucially dependent on the network symmetries. Our study demonstrates the observability of cluster synchronization in realistic systems, and indicates the feasibility of controlling network synchronization by adjusting network topology.     

Adhesion and fingering in the lifting Hele-Shaw cell: Role of the substrate

The lifting Hele-Shaw cell (LHSC) is used to study adhesion as well as viscous fingering. In the present paper we report a series of observations of development of the interface for different viscous fluids, both Newtonian and non-Newtonian, in a LHSC operated at a constant lifting force. Glass and perspex are used as the plates in two different sets of experiments. The objectives are 1) to measure the time required to separate the plates as a function of the lifting force and 2) to note the force above which viscous fingering appears. We find that for the Newtonian fluids, the plate separation time follows a universal power law with the lifting force, irrespective of fluid and substrate. The non-Newtonian fluids too, with proper scaling obey the same power law. The appearance of fingering, however, depends on the properties of the fluid as well as the substrate. We suggest a modified form of the capillary number which controls the onset of fingering; this new quantity, termed the “fingering parameter” involves the dielectric constants of the substrate and fluid in addition to the viscosity and surface tension.