无序二元合金(NixCu1-x)不同解理面上O吸附对Cu偏析的影响

应用计算机编程构造出了存在和不存在表面偏析的无序二元合金NixCu1-x(x=0.4)(100)表面及(110)表面的原子集团模型,然后按覆盖度θ=0.5,构造出了O吸附后的原子集团模型,应用Recursion方法计算了O在NixCu1-x(存在偏析和不存在偏析时)无序二元合金(100)和(110)表面吸附的电子结构.由此得出:1)O吸附使合金表面态密度峰降低,带宽加宽,并且表面Ni原子的d电子与吸附质O原子的s,p电子的共价作用比Cu更强烈;2)O吸附在NixCu1-x(x=0.4)(110)表面比(100)表面更稳定;3)O的吸附抑制了Cu在表面富集,且这种作用主要表现在表面一层.     

无序二元合金(Ni_xCu_(1-x))表面CO吸附及对表面偏析的影响

根据计算机编程构造出了存在和不存在表面偏析的无序二元合金NixCu1 -x(x =0 4 )的原子集团模型 ,然后按覆盖度θ=0 5 ,构造出了CO表面吸附的模型 ,应用Recursion方法计算了CO在NixCu1 -x(存在偏析和不存在偏析时 )合金表面不同位置 (顶位和芯位 )吸附的电子结构 .由此得出 :1 )CO在顶位吸附时较稳定 ;2 )CO吸附使合金表面态密度峰降低 ,带宽加宽 ,使d轨道的局域性变弱 ;3)CO的吸附抑制了Cu在表面富集 ,从电子层次上解释了CO吸附于NixCu1 -x对合金表面偏析的影响机理     

杂质对吸附系统O/RhxPt1-x衬底、合金(110)表面偏析的影响

构造了考虑吸附与偏析相互作用情况下无序二元合金Rhx Pt1-x(110)吸附氧表面的原子集团模型,其中O的覆盖度为0.5;构造了考虑杂质Ni,Cu,W对合金可能产生影响的吸附表面原子集团模型,杂质的掺入采用替位式.应用recursion方法计算了合金表面的环境敏感镶嵌能和电子结构.环境敏感镶嵌能计算表明杂质Ni,Cu和W均使O吸附RhxPt1-x(110)合金表面偏析情况发生逆转,Ni对Rh-Pt合金偏析的影响最大,其次是Cu,W对合金偏析的影响最小;电子结构计算表明杂质Ni,Ca W存在于合金表面时,使Rh与O的共价相互作用减弱,使表面偏析发生逆转,Pt再次偏析于表面.     

无序二元合金（NixCu1－x）不同解理面上O吸附对Cu偏析的影响

应用计算机编程构造出了存在和不存在表面偏析的无序二元合金Ni_xCu_1-x (x=0.4)(１００)表面及(１１０)表面的原子集团模型，然后按覆盖度θ=0.5，构造 出了O吸附后的原子集团模型，应用Recursion方法计算了O在Ni_xCu_{1-x(存在偏析和不存在偏析时)无序二元合金(１００)和(１１０)表面吸附的电子结构.由此 得出：1)O吸附使合金表面态密度峰降低，带宽加宽，并且表面Ni原子的d电子与吸附质O原 子的s，p电子的共价作用比Cu更强烈；2)O吸附在NixCu1-x(x=0.4) (１１０)表面比(１００)表面更稳定；3)O的吸附抑制了Cu在表面富集，且这种作用主要表 现在表面一层. 关键词： 化学吸附 表面偏析 Recursion方法 态密度}     

杂质对吸附系统O/RhxPt1-x衬底合金(110)表面偏析的影响

构造了考虑吸附与偏析相互作用情况下无序二元合金Rh_xPt_1-x(110)吸附氧表面的原子集团模型,其中O的覆盖度为0.5;构造了考虑杂质Ni,Cu,W对合金可能产生影响的吸附表面原子集团模型,杂质的掺入采用替位式.应用recursion方法计算了合金表面的环境敏感镶嵌能和电子结构.环境敏感镶嵌能计算表明杂质Ni,Ｃu和Ｗ均使O吸附Rh_xPt_1-x(110)合金表面 关键词： 化学吸附 表面偏析 recursion方法 态密度     

无序二元合金（NixCu1-x）表面CO吸附及对表面偏析的影响

根据计算机编程构造出了存在和不存在表面偏析的无序二元合金Ni_xCu_1-x（x=0.4）的原子集团模型，然后按覆盖度θ=0.5，构造出了CO表面吸附的模型 ，应用Recursion方法计算了CO在（Ni_xCu_1-x）（存在偏析和不存在偏析时）合金表面不同位置（顶位和芯位）吸附的电子结构 .由此得出：1)CO在顶位吸附时较稳定；2)CO吸附使合金表面态密度峰降低，带宽加宽，使d轨道的局域性变弱；3)CO的吸附抑制了Cu 关键词： 化学吸附 表面偏析 Recursion方法 态密度     

CO和O在无序二元合金NiCu表面上的化学吸附

本文用一维紧束缚模型和单电子化学吸附理论,在平均T矩阵近似下,研究了CO和O在无序二元合金Ni_xCu_1-x表面上的化学吸附特性,结果表明,CO和O在Ni_xCu_1-x表面上的化学吸附具有类似的性质,随合金中Ni浓度的增加,化学吸附能降低,化学吸附加强,Cu在NiCu合金表面的偏析在一定程度上减弱了CO和O在NiCu表面上的吸附。 关键词：     

面心立方(001)方向AB合金薄膜表面层的有序无序相变

采用平均场近似方法对两组元面心立方合金薄膜的有序无序相转变过程进行模拟计算，结果表明，合金薄膜的有序无序相变受薄膜层数奇偶性的影响.薄膜层数奇偶性不同，会导致薄膜具有不同的相结构和热力学性质.在弱表面偏析作用下，对于偶数层薄膜，由于薄膜边界对称性破缺，对应体组分x=0.5的化学势区间，偶数层薄膜有序无序相变过程中出现了中间温度相和浸润现象.而奇数层薄膜的有序无序相变类似体材料的相变.在强表面偏析作用下，由于受表面偏析作用和有限尺寸效应影响，对应体组分x=0.5的化学势区间，奇数层薄膜中出现AB(AB)关键词： 合金薄膜 有序无序相变 浸润现象 准热力学相变     

基于密度泛函理论的DBDS与DBS对铜绕组腐蚀性能对比研究

二苄基二硫醚(DBDS)与二苄基硫醚(DBS)是变压器内部主要腐蚀性硫化物,能腐蚀铜绕组,破坏变压器的安全运行.为从微观层面探究两者腐蚀性能的差异,基于密度泛函理论(DFT)对DBDS与DBS的腐蚀性能进行对比研究.计算了DBDS/Cu(110)吸附模型与DBS/Cu(110)吸附模型的功函变化,发现DBDS/Cu(110)的功函变化ΔΦ_1(-0.388 eV)绝对值要小于DBS/Cu(110)功函变化ΔΦ_2(-1.118 eV)绝对值,说明DBS更易吸附Cu(110)表面;DBDS在Cu(110)表面的吸附能E_(ads1)为8.571 eV,DBS在Cu(110)表面吸附能E_(ads2)为6.077 eV,表明两者都不能自发吸附,需要从外界吸热才能吸附,且DBS从外界获取能量更少,更容易吸附.同时比较了DBDS分子与DBS分子前线轨道分布以及HOMO轨道与LUMO轨道能量差,计算了DBDS分子与DBS分子的电负性,结果表明:DBDS电负性大小为3.132 eV,DBS电负性大小为3.100 eV,两者基本相等.而DBDS前线轨道能量差(2.610 eV)明显小于DBS前线轨道能量差(3.610 eV), DBDS优化前后的S-S键长分别为2.033?和3.057?,说明DBDS更容易与Cu发生反应.以上模拟结果说明,DBS更易吸附于Cu,而DBDS更易与Cu发生反应.     

CuAg纳米结构表面共存和Ag表面对甘氨酸的新吸附行为

在异质纳米结构表面发生的新现象是当前研究的热点.最近发现，尽管甘氨酸在纯Ag表面只 能作物理吸附，蒸镀在Cu表面的单层Ag岛却能在Cu的帮助下，出现对甘氨酸作化学吸附的能力，这种现象是溢流效应的一种反映.蒸镀在Ag表面的Cu岛也能帮助附近裸露的Ag表面获得 化学吸附甘氨酸的能力，虽然这里已不是单原子层的银了.结果说明这种溢流现象来源于CuA g在表面的纳米结构共存，而不只是这种共存的某个结构所特有的.但是，由于Cu的表面能大 于Ag，所以即使是在室温下，Cu岛也会逐渐地被一单层Ag原子完全覆盖，从而失去溢 关键词： 溢流 甘氨酸 Cu Ag(111)     

Research of the behaviour of O chemisorption on the (110) surface of Rhx--Pt1－x alloy

An atomic group model of the disordered binary alloy Rhx-Pt1-x has been constructed to investigate surface segregation. According to the model, we have calculated the electronic structure of the Rhx-Pt1-x alloy surface by using the recursion method when O atoms are adsorbed on the Rhx-Pt1-x （110） surface under the condition of coverage 0.5. The calculation results indicate that the chemical adsorption of O changes greatly the density of states near the Fermi level, and the surface segregation exhibits a reversal behaviour. In addition, when x 〈 0.3, the surface on which O is adsorbed displays the property of Pt; whereas when x 〉 0.3 it displays the property of Rh.     

Equilibrium and kinetic surface segregation in binary alloy thin films

A general theoretical analysis of the effect of film thickness on equilibrium and kinetic surface segregation in binary alloy thin films is presented. In this analysis, a constrained condition that represents the finite size of thin film system has been introduced to the modified Darken model, which has been used to describe both equilibrium and kinetic surface segregation in bulk materials. Simulation of surface segregation for alloy thin films can be carried out for all composition ranges and all film thicknesses if only knowing the surface segregation parameters for bulk materials. Simulations of equilibrium and kinetic surface segregation in Cu(1 1 1)Ag binary alloy thin film are presented.     

Phase equilibrium of Cd_(1-x)Zn_xS alloys studied by first-principles calculations and Monte Carlo simulations

The first-principles calculations based on density functional theory combined with cluster expansion techniques and Monte Carlo(MC) simulations were used to study the phase diagrams of both wurtzite(WZ) and zinc-blende(ZB)Cd_(1-x)Zn_xS alloys.All formation energies are positive for WZ and ZB Cd_(1-x)Zn_xS alloys,which means that the Cd_(1-x)Zn_xS alloys are unstable and have a tendency to phase separation.For WZ and ZB Cd_(1-x)Zn_xS alloys,the consolute temperatures are 655 K and 604 K,respectively,and they both have an asymmetric miscibility gap.We obtained the spatial distributions of Cd and Zn atoms in WZ and ZB Cd_(0.5)Zn_(0.5)S alloys at different temperatures by MC simulations.We found that both WZ and ZB phases of Cd_(0.5)Zn_(0.5)S alloy exhibit phase segregation of Cd and Zn atoms at low temperature,which is consistent with the phase diagrams.     

Surface segregation in a Ni-1 at% Pd alloy

The surface composition of a Ni-1 at% Pd alloy has been determined by Auger electron spectroscopy after equilibration of the alloy at several temperatures in the range 550 to 800°C. Moderate segregation of Pd to the surface of the alloy has been observed, with concentrations of up to ~～30 at% being detected at the surface after equilibration at 550°C. The heat of segregation (or adsorption) of Pd has been found to agree reasonably well with the predictions of a previously developed unified model of surface segregation in alloys. The kinetics of Pd segregation to the surface have also been measured between 500 and 700°C. Analysis of the kinetic data yields apparent diffusivities of Pd through the alloy that are suggestive of a dominant grain boundary transport mechanism.     

A Monte Carlo study of surface segregation in alloys

The Monte Carlo method has been applied to the study of surface segregation in a multi-layer, regular solution model of alloy surfaces. Three different alloy configurations have been investigated: semi-infinite slabs, thin films and small particles. The results show that the alloy component with the lowest surface energy tends to segregate to the first three or four surface atom layers and that segregation is greater in clustering alloys than in ordering alloys. Furthermore, segregation is more pronounced in low coordination surfaces, as evidenced by a comparison of {110} and {100}-oriented surfaces of fcc alloys. The degree of surface segregation in thin films and small particles (in the particle size range studied) tends to be smaller than in semi-infinite slabs, because of mass conservation constraints, and decreases with decreasing film thickness and particle size. The results obtained are contrasted with previous calculations and possible avenues for improving surface segregation models are discussed.     

Formation of high-Sn content polycrystalline GeSn films by pulsed laser annealing on co-sputtered amorphous GeSn on Ge substrate

Polycrystalline Ge_(1-x)Sn_x(poly-Ge_(1-x)Sn_x) alloy thin films with high Sn content( 10%) were fabricated by cosputtering amorphous GeSn(a-GeSn) on Ge(100) wafers and subsequently pulsed laser annealing with laser energy density in the range of 250 mJ/cm~2 to 550 mJ/cm~2. High quality poly-crystal Ge_(0.90) Sn_(0.10) and Ge_(0.82) Sn_(0.18) films with average grain sizes of 94 nm and 54 nm were obtained, respectively. Sn segregation at the grain boundaries makes Sn content in the poly-GeSn alloys slightly less than that in the corresponding primary a-GeSn. The crystalline grain size is reduced with the increase of the laser energy density or higher Sn content in the primary a-GeSn films due to the booming of nucleation numbers. The Raman peak shift of Ge-Ge mode in the poly crystalline GeSn can be attributed to Sn substitution, strain,and disorder. The dependence of Raman peak shift of the Ge-Ge mode caused by strain and disorder in GeSn films on full-width at half-maximum(FWHM) is well quantified by a linear relationship, which provides an effective method to evaluate the quality of poly-Ge_(1-x)Sn_x by Raman spectra.     

Nanoscale structural investigation of Zn_(1-x)Mg_xO alloy films on polar and nonpolar ZnO substrates with different Mg contents

Zn_(1-x)Mg_xO alloy films are important deep ultraviolet photoelectric materials.In this work,we used plasma-assisted molecular beam epitaxy to prepare Zn_(1-x)Mg_xO films with different magnesium contents on polar(0001) and nonpolar(1010) ZnO substrates.The nanoscale structural features of the grown alloy films as well as the interfaces were investigated.It was observed that the cubic phases of the alloy films emerged when the Mg content reached 20% and 37% for the alloy films grown on the(0001) and(1010) ZnO substrates,respectively.High-resolution transmission electron microscopy images revealed cubic phases without visible hexagonal phases for the alloy films with more than 70% magnesium,and the cubic phases exhibited three-fold and two-fold rotations for the alloy films on the polar(0001) and nonpolar(1010) ZnO substrates,respectively.This work aims to provide references for monitoring the Zn_(1-x)Mg_xO film structure with respect to different substrate orientations.