Cu 表面性质的第一性原理分析

采用第一性原理赝势平面波方法, 计算并详细分析了面心立方Cu晶体及其 (100), (110) 和 (111) 这3个低指数表面的原子结构、 表面能量及表面电子态密度. 表面能的计算结果表明, Cu (111) 表面的结构稳定性最好, Cu (100) 表面次之, Cu (110)表面的结构稳定性最差. 3个表面的表面原子弛豫量随着层数的增加而逐渐减弱. Cu (110) 表面的最表层原子相对收缩最大, Cu (100)表面次之, Cu (111) 表面的最表层原子相对收缩最小. 表面原子弛豫不仅引起表面几何结构的变化, 而且使表面层原子的电子态密度峰形相对晶体内部发生变化, 这是表面能产生的主要原因, 而Cu (110)表面相对于Cu (100)与Cu (111)表面具有高表面活性的主要原因则源于其表面层原子电子态密度在高能级处的波峰相对晶体内部显著的升高. 关键词： Cu 晶体 表面结构 表面能 态密度     

fcc金属层错能的EAM法计算

采用嵌入原子法(EAM)计算了Cu，Ag，Au，Ni，Al，Rh，Ir，Pd，Pt和Pb等10种面心立方(fcc)金属的层错能，除Rh和Ir两种金属外，其他金属的计算结果和实验结果基本一致. 关键词： 面心立方金属 层错能 EAM     

fcc金属表面能的各向异性分析及表面偏析的预测

本文将元素变量(φ^*和n_WS)和MAEAM相结合,从原子尺度上对10种fcc金属Cu,Ag,Au,Ni,Pd,Pt,Rh,Al,Ir和Pb的38个不同晶面的表面能进行模拟计算及各向异性分析. 结果表明,fcc金属的密排面(111)的表面能最小,则该晶粒取向优先生长,与实验结果和第一原理的LMTO-ASA计算结果一致;各个晶面的表面能均随着其他晶面与(111)晶面的夹角cosθ_(hkl)的增长而呈线性 关键词： FCC金属 MAEAM 表面能 表面偏析     

UO2 晶体中低密勒指数晶面表面能的分子动力学模拟

采用基于刚性离子势的分子动力学模拟方法初步计算了UO₂晶体中(100), (110)和(111) 3种低密勒指数晶面在300–1500 K范围内的表面能大小. 结果表明, 3种晶面的表面能大小随温度的升高而降低, 与实验结果趋势一致; 原子排列最紧密的(111)晶面具有最低的表面能, 3种晶面的表面能大小从高到低依次为(100), (110)和(111)晶面; 达到平衡状态下的表面层原子相对于体内原子层在表面的法线方向上发生了明显的压缩并且表面层原子的对称性也降低了, 表面原子的弛豫效应一直影响到了第5层. 计算研究结果将有助于深入认识UO₂燃料中裂变气体气泡的聚集长大以及燃料的辐照肿胀开裂行为. 关键词： 分子动力学 2')" href="#">UO₂ 低密勒指数晶面 表面能     

带电胶体粒子结晶过程的实验研究

利用带电单分散聚苯乙烯胶体粒子，通过自组装机理，制备了体积百分比为4.8%的具有多晶结构的胶体晶体，并用Kossel衍射技术和紫外可见分光光度计分别对晶体的生长过程进行了监测.通过对Kossel的图像分析检测不同阶段相应的晶格结构，发现胶体结晶过程晶体结构演变顺序为由液态—随机层结构—堆无序结构—面心立方孪晶结构到面心立方结构.定量地确定了结晶过程中晶体不同晶面的晶面间距和晶体的晶格常数，通过紫外可见分光光度计测量的晶体透射谱图，计算得到111晶面的晶面间距和晶体的晶格常数，与用Kossel衍射技术得到的结果相一致，还发现随样品放置时间的延长，衰减峰变窄和加深，并向短波方向移动，对应着晶体的晶格常数减小的现象. 关键词： 胶体晶体 自组织 Kossel环 聚苯乙烯粒子     

名词浅释

知识与进展晶体对称轴和对称面 晶体是由按一定对称性排列成点阵的原子所组成.如果一个晶体结构对某个轴(或面)而言,按一定对称操作(如旋转或反射),便能使该晶体结构自身完全重合,则此轴为晶体的对称轴,相应的面为对称面.低密勒指数面、低标次轴 给出在一个晶面上的三个不共线的原子的坐标,就决定了该晶面的位置和取向,通常用密勒指数指明面的取向,因而把晶面记为(h,k,l),密勒指数低的面,也就是h,k,l值小的面,如立方晶体表面为(100),(010),(001),(100),(010)和(001),属于低密勒指数面。 晶体旋转对称轴可以分为一重、二重、三重、四重和六重…     

沿〈111〉晶向冲击加载下铜中纳米孔洞增长的塑性机制

用分子动力学方法计算模拟了单晶铜中纳米孔洞（约φ1．3nm）在〈111〉晶向冲击加载过程中的演化及其周围区域发生塑性变形的过程。模拟结果的原子图像如图1所示，其中活塞速度为500m／s，图中所示为4族连续三层穿过孔洞中心的{111}晶面在4000个时间步时（处于拉伸应力状态）的原子排列图像。从面心立方铜晶体中位错成核及运动特点可知，当位错在{111}面上成核和运动后，将产生层错和部分位错结构，我们正是根据此特点来判断在某{111}晶面上是否有位错的成核和运动。从图1可以看到，沿〈111〉晶向冲击加载后，     

FCC金属空位的MAEAM理论研究

应用涉及更远邻原子的改进分析型嵌入原子方法(MAEAM)计算了面心立方(fcc)金属(Ag,Al,Au,Cu,Ir,Ni,Pd,Pt,Rh)的空位性能.在MAEAM计算中,考虑了远邻原子相互作用和单空住迁移能,对两体势进行了坚挺处理,并采用新的截尾函数和加强光滑连接条件对两体势作了截尾处理.同时为了更好的符合面心立方晶体的结合能、弹性常数和平衡条件,调整了多体势的模型常数.未弛豫空住性能计算中考虑了两体势的截尾距离和电子密度分布函数的截尾距离之间近邻原子的作用以及双空位迁移途径周围的原子非对称分布.结果与其它方法计算结果基本一致,但更加接近实验值.对双空住迁移能的计算结果有利地说明了fcc金属双空住5种迁移途径的扩散机制.     

不同晶体模型的微波布拉格衍射

研究了不同晶体模型下布拉格衍射规律,讨论了简单立方(100)晶面微波衍射图出现2级衍射和3级衍射所需的条件.将简单立方模型改造成四方模型,讨论了四方晶体模型的衍射峰随晶面间距的变化规律.设计了体心和底心立方模型,并观察到了(100)晶面的消光现象.采用有限点阵理论模拟计算结果也与实验测量数据一致.     

Mo纳米薄膜热力学性质的分子动力学模拟

采用改进嵌入原子法(MAEAM),通过经典的分子动力学(MD)模拟计算了高熔点过渡金属体心立方(bcc) Mo块体Gibbs自由能和表面能. 对于纳米薄膜的热力学数据,比如Gibbs自由能等,可以看成是薄膜内部原子和表面原子两部分数据之和,然后根据薄膜的体表原子之比就可以直接计算出总的自由能,并由此可以得到热力学性质与薄膜尺寸及温度的定量关系式. 分别计算了bcc Mo块体及其纳米尺寸薄膜的自由能和热容,结果表明,Mo纳米薄膜的热力学性质具有尺寸效应,并且在薄膜尺寸小于15—20nm时,这种效应变得非常明 关键词： 改进嵌入原子法 Mo纳米薄膜 表面自由能 热容     

Calculation of the surface energy of fcc metals with modified embedded-atom method

The surface energies for 38 surfaces of fcc metals Cu, Ag, Au, Ni, Pd, Pt, A1, Pb, Rh and Ir have been calculated by using the modified embedded-atom method. The results show that, for Cu, Ag, Ni, A1, Pb and Ir, the average values of the surface energies are very close to the polycrystalline experimental data. For all fcc metals, as predicted, the close-packed (111) surface has the lowest surface energy. The surface energies for the other surfaces increase linearly with increasing angle between the surfaces (hkl) and (111). This can be used to estimate the relative values of the surface energy.     

Computer simulation of symmetrical tilt grain boundaries in noble metals with MAEAM

This paper reports that an atomic scale study of [\bar {1}10] symmetrical tilt grain boundary (STGB) has been made with modified analytical embedded atom method (MAEAM) for 44 planes in three noble metals Au, Ag and Cu. For each metal, the energies of two crystals ideally joined together are unrealistically high due to very short distance between atoms near the grain boundary (GB) plane. A relative slide between grains in the GB plane results in a significant decrease in GB energy and a minimum value is obtained at specific translation distance. The minimum energy of Cu is much higher than that of Ag and Au, while the minimum energy of Ag is slightly higher than that of Au. For all the three metals, the three lowest energies correspond to identical (111), \mbox(113) and \mbox(331) boundary successively for two translations considered; from minimization of GB energy, these boundaries should be preferable in [\bar {1}10] STGB for noble metals. This is consistent with the experimental results. In addition, the minimum energy increases with increasing reciprocal planar coincidence density \Sigma, but decreases with increasing relative interplanar distance d /a.     

Binding states and decomposition of NO on single crystal planes of Pt

Nitric oxide desorption and reaction kinetics are compared on the (111), (110),and (100) planes of platinum using temperature programmed desorption mass spectrometry. NO exhibits large crystallographic anisotropies with the (100) plane having stronger bonding and much higher decomposition activity than the (110) or (111) planes. The desorption activation energies for the major tightly bound states are 36, 33.5, and 25 kcal mole^?1 on the (100), (110), and (111) planes respectively. Pre-exponential factors for these states on the (110) and (111) planes are 1 × 10^16±0.5s^?1. The major tightly bound state on the (100) plane dissociates to yield 50% N₂ and O₂, but all other states all planes desorb without significant decomposition. The fraction decomposed is less than 2% on the Pt(111) surface.     

Reconstructed (1 1 0) surfaces of FCC transition metals

The energies of the ideal, missing row (MR) and missing column (MC) (1 1 0) surfaces have been calculated by using modified embedded atom method (MEAM) for seven face centered cubic (FCC) transition metals Au, Pt, Ag, Pd, Rh, Cu and Ni. The results, that the MC reconstruction can not be formed for all metals, while the MR reconstruction can be formed naturally for Au and Pt, inductively for Ag, Pd, Rh and Cu and difficultly for Ni, are better than EAM calculated results in comparing with experimental results. In addition to the surface energy explanation, the results are also related to the surface topography and valence electron structure.     

UHV-SEM observations of cleaning process and step formation on silicon (111) surfaces by annealing

The cleaning process and step formation by high temperature annealing up to 1250°C on the Si(111) surface are observed by an ultra-high-vacuum scanning electron microscope (UHV-SEM). The clean surface is composed of alternate planes of terraces and step bands with widths of several μm and 1 μm, respectively, in the 〈1?1?2〉 direction. Both planes are inclined by about 10° to each other. The surface steps are not only monolayer steps, but also higher steps comprising several monolayers. Monolayer steps join to form a high step, and 70–80 steps of several monolayers high form a step band by bunching in an average distance of several hundred A toward the 〈1?10〉 direction. The step structure depends on the annealing temperature and on the angle at which the cutting plane is off from the exact 〈111〉 orientation. In several studies of high energy reflection electron microscopy under small grazing angle incidence monolayer steps were observed on the terrace, but no rough structures like the step bands and high steps could be discerned. The step structure observed by the present experiment is compared with those observed by previous workers.     

Asymmetric tilt grain boundary structure and energy in copper and aluminium

Atomistic simulations were employed to investigate the structure and energy of asymmetric tilt grain boundaries in Cu and Al. In this work, we examine the Σ5 and Σ13 systems with a boundary plane rotated about the ? 100 ? misorientation axis, and the Σ9 and Σ11 systems rotated about the ? 110 ? misorientation axis. Asymmetric tilt grain boundary energies are calculated as a function of inclination angle and compared with an energy relationship based on faceting into the two symmetric tilt grain boundaries in each system. We find that asymmetric tilt boundaries with low index normals do not necessarily have lower energies than boundaries with similar inclination angles, contrary to previous studies. Further analysis of grain boundary structures provides insight into the asymmetric tilt grain boundary energy. The Σ5 and Σ13 systems in the ? 100 ? system agree with the aforementioned energy relationship; structures confirm that these asymmetric boundaries facet into the symmetric tilt boundaries. The Σ9 and Σ11 systems in the ? 110 ? system deviate from the idealized energy relationship. As the boundary inclination angle increases towards the Σ9 (221) and Σ11 (332) symmetric tilt boundaries, the minimum energy asymmetric boundary structures contain low index {111} and {110} planes bounding the interface region.     

Theoretical strength and cleavage of diamond

The theoretical strength of diamond has been calculated for the <100>, <110>, and <111> directions using a first principles approach and is found to be strongly dependent on crystallographic direction. This elastic anisotropy, found at large strains, and particularly the pronounced minimum in cohesion in the <111> direction, is believed to be the reason for the remarkable dominance of the 111 cleavage plane when diamond is fractured. The extra energy required to cleave a crystal on planes other than 111 is discussed with reference to simple surface energy calculations and also the introduction of bond-bending terms.     

BTA在铜表面吸附的密度泛函理论研究

本文基于密度泛函理论(DFT)的第一性原理研究了苯并三氮唑(BTA)分子吸附于铜表面的反应活性特征及其吸附在三种不同取向晶面时的电荷转移以及成键情况,结果表明：BTA分子的亲电和亲核活性中心为N(1)、N(2)和C(5),在铜表面垂直吸附时为化学吸附,Cu原子的最外层价电子转移到N(2)原子上,两者形成配位键;BTA分子在三种不同取向的铜表面吸附时的吸附能大小为：Cu(110)_x>Cu(100)_x>Cu(111)_x(x=T、B、H),T表示顶位,B表示桥位,H表示空位;BTA吸附在Cu(111)面的转移电荷量：T(顶位)>B(桥位)>H(空位).