金刚石(001)表面台阶结构的第一原理研究

半导体表面一个最普遍存在的现象是发生晶格再构,它导致了表面具有各种不同于体内的物理性质.正是由于表面再构在基础和应用研究方面具有的重要性,几十年来人们做了大量的工作. 金刚石(001)表面的台阶结构如图1所示[1],其中S(single)表示单层,D(double)表示双层,A代表台阶方向与上台面的二聚体方向相垂直,B代表台阶方向与上台面的二聚体方向相平行. 在计算中采用了平面波赝势法[2].相互作用采用Vanderbilt超软赝势,交换关联能采用GGA近似,波函数的截断能量是350 eV.计算中优化的晶格常量a=0.357 4 nm.简约Brillouin中的k点选取为4×4×1.     

GaAs(110) 弛豫表面电子结构的理论研究

基于 K.S.Dy 的无穷阶微扰理论及紧束缚方法,取用 Vogl 的经验紧束缚参数,我们对 GaAs(110) 表面的电子结构做了理论计算,并同实验进行了比较,得出了 BR 模型比较接近真实表面构型的结论。     

铝(210)表面的LEED,AES研究

采用低能电子绕射(LEED)和俄歇电子能谱(AES)的方法,研究了铝(210)表面的弛豫和表面结构。按多童散射理论,使实验测得的和计算的LEED谱有较好的吻合。结果表明:铅(210)表面的弛豫仲展至表面五个原子层,且垂直于表面的驰豫较平行于表面的弛豫显著得多。最后用静电模型对这些结果进行了讨论。     

新鲜多孔硅(001)表面结构与电子特性理论研究

在周期边界条件下的k空间中,采用基于密度泛函理论的广义梯度近似(GGA)平面波超软赝势法,建立H12S i31几何模型来对表面主要被H覆盖的新鲜多孔硅(Porous S ilicon,PS)(001)表面最外层的S i—H键的几何结构和电子特性进行初步的理论研究.计算得到氢化PS(001)表面几何结构S i—H键长为0.148 nm、H—S i—H键角为106°,并通过原子布居数、电子密度图分析得到氢化PS表面原子的电子特性.     

无序 FCC TixAl(1-x)合金的电子结构和热力学性质

应用合金系统科学(SSA)框架,确定FCC Ti-Al合金系结构参数和性质及相应特征晶体的基本信息;在FCC Ti-Al系中,通过SSA框架计算得到Ti和Al特征原子序列的电子结构和性质;确定新的Gibbs能函数与结构参数和性质能紧密关联。研究结果表明,应用特征原子排列设计可设计无序和有序合金,它们的电子结构、晶格常数、物理性质和热力学性质随成分的变化都可由此求得。     

盐生植物耐盐结构的研究现状(综述)

盐生植物在对盐渍环境的适应过程中,形成了特有的结构。从根、茎、叶三方面总结了盐生植物的耐盐结构特点,旨在为盐生植物的研究提供更多的植物体微观结构资料。     

GaAs(114)A表面投影能带和表面态分析

基于GaAs(114)A表面的几何结构，采用散射理论的格林函数方法，首次从理论上计算了GaAs（114）A表面的电子结构，得到了该表面的投影能带结构，并从键合结构上分析了各表面态的轨道特征和色散特性，结果表明，在基本带隙中有4个表面态，异极带隙中有2个表面态，这些表面态分别与表面的离子悬挂键相对应。     

结构应力S(t)的几何更新过程模型

本文讨论结构在设计基准期[0,T]内应力出现规律,考虑应力出现时间问隔是一串独立服从相同几何分布的随机变量,建立更新过程模型.给出在[0,T]内应力出现的概率分布,更新函数与更新方程表述式,平均期望更新个数的收敛性。同时,讨论结构应力S(t)的最大值S_u的概率分布。     

掠入射荧光XAFS研究(Ge4/Si4)5/Si(001)超晶格的结构

本文用掠入射荧光XAFS研究(Ge4/Si4)5/Si(001)形变超晶格的局域结构.超晶格中的Ge-Ge和Ge-Si第一配位键长分别为RGe-Ge=0.243 nm和RGe-Si=0.238 nm,与晶态Ge(RGe-Ge=0.245 nm)和共价Ge-Si键长RGe-Si=0.240 nm相比,其配位键长缩短了0.002 nm,表明Ge原子周围的晶格产生了扭曲,Ge-Ge配位数为1.8和Ge-Si配位数为2.2显然偏离了理论的配位数Ge-Ge为3和Ge-Si配位数为1.我们提出Ge和Si原子的位置交换模型来解释(Ge4/Si4)5超晶格的界面结构.     

GaN,AlN和BN(110)表面反常弛豫的电子结构计算

在紧束缚模型框架下采用形式散射理论方法计算了具有闪锌矿结构的化合物半导体GaN,AlN和BN(110)反常弛豫表面的表面电子结构，讨论了表面弛豫对表面电子结构的影响，并将结果同GaAs(110)表面的表面电子结构作了比较.     

PbWO4晶体中铅空位周围晶格弛豫的研究

使用相对论性密度泛函计算程序，按照能量最低原理采用共轭梯度方法，对缺铅的钨酸铅晶体进行结构优化处理．计算了铅空位周围晶格的弛豫，得到铅空位周围的晶格结构．结果表明，铅空位周围次近邻的正离子(Pb^2 和W^6 )向铅空位迁移，而铅空位周围最近邻的负离子(O^2-)向远离铅空位的方向迁移．晶格的驰豫结果使铅空位处的电负性降低．     

CoSi2（001）表面的第一原理计算

基于广义梯度近似的从头算平面波超软赝势方法,考虑了CoSi2（001）面的Si和Co两种终止表面。结果表明表面能较低的Si终止表面比Co终止表面稳定。但是,由于差距不大,这两种终止表面可以共同存在。两种不同终止表面第1层原子与第2层原子弛豫后的间距都变小,Si终止表面的表面四层间距弛豫量略大于Co终止表面。     

Theoretical calculations on the atomic and electronic structure of β-SiC(110) surface

We present a theoretical calculation of the atomic and electronic structure of β-SiC and its non-polar (110) surface using the full potential linear augmented plane wave (FPLAPW) approach. The calculated lattice constant and bulk modulus of β-SiC crystal are in excellent agreement with experimental data. The atomic and electronic structure of β-SiC(110) surface has been calculated by employing the slab and supercell model. It is found that the surface is characterized by a top-layer bond-length-contracting rotation relaxation in which the Si-surface atom moves closer towards the substrate while the C-surface atom moves outward. This relaxation is analogous to that of Ⅲ-Ⅴ semi-conductor surface. The driving mechanism for this atomic rearrangement is that the Si atom tends to a planar sp2-like bonding situation with its three N neighbors and the N atom tends to a p3-like bonding with its three Si neighbors. Furthermore, surface relaxation induces the change from metallic to semiconducting characterization.     

Theoretical calculations on the atomic and electronic structure of β-SiC(110) surface

We present a theoretical calculation of the atomic and electronic structure of β-SiC and its non-polar (110) surface using the full potential linear augmented plane wave (FPLAPW) approach. The calculated lattice constant and bulk modulus of β-SiC crystal are in excellent agreement with experimental data. The atomic and electronic structure of β-SiC(110) surface has been calculated by employing the slab and supercell model. It is found that the surface is characterized by a top-layer bond-length-contracting rotation relaxation in which the Si-surface atom moves closer towards the substrate while the C-surface atom moves outward. This relaxation is analogous to that of Ⅲ-Ⅴ semiconductor surface. The driving mechanism for this atomic rearrangement is that the Si atom tends to a planar sp²-like bonding situation with its three N neighbors and the N atom tends to a p³-like bonding with its three Si neighbors. Furthermore, surface relaxation induces the change from metallic to semiconducting characterization.     

螺杆几何形状参数对多功能食品加工成型机性能的影响

全面分析了螺杆的几何形状参数对多功能食品加工成型机的性能影响,对螺杆的合理设计乃至整机的设计都有着很重要的实际指导意义.     

第一性原理计算锐钛矿（101）面的电子结构

采用基于密度泛函理论的平面波赝势方法计算了锐钛矿（101）表面的电子结构．首先对锐钛矿完整（101）表面模型进行结构优化,在此基础上计算了电子结构,得到了能带结构和态密度等数据．结果分析表明表面的电子结构与体相基本相同,在完整表面上没有出现表面态,驰豫后完整的锐钛矿（101）表面是稳定的,表面价带主要由O2p组成,导带主要由Ti3d组成,表面导带态密度变窄导致表面能隙比体相能隙略增大．通过表面原子局域态密度和Mulliken净电荷的分析,推测O2c、O3c、Ti5c可能是活性位置．     

First-principles investigation on initial stage of 2H-SiC(001) surface oxidation

We present comprehensive first-principles calculations on the initial stages of SiC oxidation by atomic oxygen on the 2H-SiC(001) surface. In order to study the kinetics of oxygen incorporation at the 2H-SiC(001) surface, we investigated adsorption and diffusion of oxygen atoms and SiO₂ nucleation. The adsorption sites, corresponding to the local minima of the potential energy surface (PES) for isolated adatoms, were identified through a comparative study of the adatom binding energy at different locations. We found that the Bridge (siloxane) site is preferred over other adsorption sites. There is no energy barrier at 0K for oxygen insertion into this site. The diffusion energy barriers that the adatom has to overcome when jumping between two adsorption sites were calculated. The premises of silica nucleation were investigated by calculating the modifications of the oxygen atom binding energy due to the interaction with neighboring adatoms. Supported by Snecma Propulsion Solide (Contract FPR No. 0539298A), Natural Science Foundation of China (Grant No 50802076) and Flying Star Program of Northwestern Polytechnical University of China     

The structure and chemistry of the TiO(2)-rich surface of SrTiO(3) (001)

Oxide surfaces are important for applications in catalysis and thin film growth. An important frontier in solid-state inorganic chemistry is the prediction of the surface structure of an oxide. Comparatively little is known about atomic arrangements at oxide surfaces at present, and there has been considerable discussion concerning the forces that control such arrangements. For instance, one model suggests that the dominant factor is a reduction of Coulomb forces; another favours minimization of 'dangling bonds' by charge transfer to states below the Fermi energy. The surface structure and properties of SrTiO(3)--a standard model for oxides with a perovskite structure--have been studied extensively. Here we report a solution of the 2 x 1 SrTiO(3) (001) surface structure obtained through a combination of high-resolution electron microscopy and theoretical direct methods. Our results indicate that surface rearrangement of TiO(6-x) units into edge-sharing blocks determines the SrO-deficient surface structure of SrTiO(3). We suggest that this structural concept can be extended to perovskite surfaces in general.     

煤表面结构介观表象的原子力显微镜(AFM)观测

针对煤复杂的表面结构,运用原子力显微镜(AFM)观测介观尺度下煤表面特征的研究方法,对煤表面形貌进行了初步观测,获得煤样的二维和三维表面形貌图,并进行了煤表面的粒度、粗糙度及功率谱分析.分析结果表明:幅度参数是表征煤样表面粗糙度的特征参数之一;利用功率谱密度有助于分析煤表面的分形特征,将AFM用于煤的表面结构特征研究,为研究煤表面介观特征提供了新的研究方法.