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}     

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.     

MnxSi1-x磁性薄膜的结构研究

利用X射线衍射(XRD)和X射线吸收近边结构(XANES)方法研究了在Si(100)衬底上及600℃温度条件下用分子束外延(MBE)共蒸发方法生长的Mn_xSi_1-x磁性薄膜的结构.由XRD结果表明,只有在高Mn含量(8％和17％)样品中存在着Mn₄Si₇化合物物相.而XANES结果则显示,对于Mn浓度在0.7%到17%之间的Mn_xSi_1-x样品,其Mn原子的XANES谱表现出了一致的谱线特征.基于多重散射的XANES理论计算进一步表明,只有根据Mn₄Si₇模型计算出的理论XANES谱才能够很好的重构出Mn_xSi_1-x样品的实验XANES谱.这些研究结果说明在Mn_xSi_1-x样品中,Mn原子主要是以镶嵌式的Mn₄Si₇化合物纳米晶颗粒存在于Si薄膜介质中,几乎不存在间隙位和替代位的Mn原子. 关键词： xSi_1-x磁性薄膜')" href="#">Mn_xSi_1-x磁性薄膜 分子束外延 XRD XANES     

室温生长MgO底层诱导(001)取向FePt薄膜的有序化过程对FePt成分的依赖

室温下通过磁控溅射在表面热氧化的Si基片上生长了MgO/Fe_xPt_100-x双层膜和Fe_xPt_100-x单层膜系列样品，Fe_xPt_100-x的原子成分x=48—68.研究了热处理前后不同成分FePt薄膜的晶体结构和磁性的变化，尤其是MgO底层的引入对FePt的晶体结构和磁性的影响 关键词： FePt(001)薄膜 0相')" href="#">L1₀相     

Si1-xGex合金半导体中CiCs和CiOi缺陷随Ge含量的变化

采用从头计算(ab initio)的方法对Si和Si_1-xGe_x合金半导体材料中C_iC_s缺陷的性质进行探讨,同时也对比调查了C_iO_i缺陷在Si和Si_1-xGe_x合金中的性质. 在不同Ge含量的Si_1-xGe_{x关键词： 1-x}Ge_x合金')" href="#">Si_1-xGe_x合金 从头计算法 iC_s缺陷')" href="#">C_iC_s缺陷 iO_i缺陷')" href="#">C_iO_i缺陷     

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     

纤锌矿BexZn1-xO合金能隙弯曲系数的第一原理研究

采用密度泛函理论框架下的第一性原理平面波超软赝势方法, 对纤锌矿Be_xZn_1-xO合金进行能隙特性、弯曲系数和结构参数的计算. 结果表明: Be_xZn_1-xO合金的能隙和弯曲系数都随Be掺杂组分的增大而增大. 通过修正Be_xZn_1-xO合金的能隙值得知其合金弯曲系数b为6.02 eV, 这与实验值接近. 纤锌矿Be_xZn_1-xO合金的能隙弯曲系数过大主要来源于体积形变和电荷转移的贡献. 文中还分析了Be_xZn_1-xO合金的晶格常数、 平均键长和平均次近邻原子距离与Be组分的关系.     

甘氨酸吸附对Ni-Cu合金(110)表面偏析的影响

通过构造无序二元合金NixCu1-x(x=0.4)(110)表面的原子集团模型用来研究表面偏析. 根据这个模型，按覆盖度μ=0.33，应用Recursion方法计算了甘氨酸在NixCu1-x无序二元合金(110)表面吸附的电子结构. 结果表明，Ni0:4Cu0:6合金表面存在着Cu的偏析，甘氨酸的吸附抑制了Cu在表面的偏析，并使得合金表面的态密度在费米能级附近发生了很大变化，吸附时合金表面与甘氨酸之间发生了电荷转移.     

密度泛函理论研究CO与Nin（n=1—6）团簇的相互作用

采用密度泛函理论对CO吸附在镍团簇表面进行了系统研究.结果表明,Ni_nCO团簇的最低能量结构是在Ni_n团簇最低能量结构的基础上吸附CO生长而成,CO的吸附没有改变Ni_n团簇的结构;CO分子在Ni_n团簇表面发生的是非解离性吸附,与优化的CO键长（0.1138?nm）相比,吸附后C—O键长变长（0.1180—0.1214?nm）,表明吸附后C—O键被削弱,CO分子被活化.自然键轨道分析表明,CO分子只与最近邻的Ni原子发生相互作用;CO分子与Ni原子相互作用的本质是CO分子内的杂化轨道与Ni原子3d, 4s, 4p轨道相互作用的结果. 关键词： nCO团簇')" href="#">Ni_nCO团簇 n团簇')" href="#">Ni_n团簇 平衡结构 电子性质     

Surface segregation of the metal impurity to the (100) surface of fcc metals

The surface segregation energies for a single metal impurity to the (100) surface of nine fcc metals (Cu, Ag, Au, Ni, Pd, Pt, Rh, Al and Ir) have been calculated using the MAEAM and molecular dynamics (MD) simulation. The results show that the effect of the surface is down to the fourth-layer and an oscillatory or monotonic damping (|E ₁| > |E ₂| > |E ₃| > |E ₄|) phenomenon in segregation energy has been obtained. The absolute value of the segregation energy E ₁ for a single impurity in the first atomic layer is much higher than that in the nether layers. Thus, whether the surface segregation will work or not is mainly determined by E ₁ which is in good relation to the differences in surface energy between the impurity and host crystals ΔQ = Q _imp − Q _hos. So we conclude that an impurity with lower surface energy will segregate to the surface of the host with higher surface energy.      

Cu NMR/NQR Studies on Magnetism in Impurity/Hole-Doped Spin-Ladder Compounds

Cu nuclear magnetic resonance (NMR) spectra of impurities (Zn, Ni, and La)-doped spin-1/2 Heisenberg ladder compounds SrCu₂O₃ (Sr123) are broadened with Curie-like temperature (T) dependence. The spectra have been successfully fit by using a quasi-one-dimensional (Q1D) staggered polarization (SP) model. Such a SP has also revealed in Cu NMR measurements of Sr_14–x Ca _x Cu₂₄O₄₁ (Cax) with hole-doped ladders. The origin of possible 3D antiferromagnetic (AF) long-range ordering in (Zn and Ni)-doped Sr123 and Cax around x=12 at low T is considered to be similar. Once unpaired spins S ₀'s are induced and 3D interlayer interaction occurs, the localized spins couple in the whole system.     

Density functional theory calculation of platinum surface segregation energy in Pt3Ni (111) surface doped with a third transition metal

We have used density functional theory method to calculate the Pt surface segregation energy in the Pt₃Ni (111) surface doped with a third transition metal M and thus investigated the influence of component M on the extent of Pt segregation to the outermost layer of these Pt₃Ni/M (111) surface. As a third component in the Pt₃Ni/M (111) surface, V, Fe, Co, Mo, Tc, Ru, W, Re, Os, and Ir were predicted to lead to even more negative Pt surface segregation energies than that in the based Pt₃Ni (111) surface; Ti, Cr, Mn, Cu, Zr, Nb, Rh, Hf, and Ta would still retain the preference of Pt segregation to the surface but with less extent than the replaced Ni, while Pd, Ag, and Au would completely suppress the Pt segregation to the Pt₃Ni/M (111) surfaces. Furthermore, we examined the relation between the Pt surface segregation energy in the Pt₃Ni/M (111) surfaces and the material properties (lattice parameter, heat of solution, and Pt surface segregation energy) of binary alloys Pt₃M. It was found that the surface energy effect, strain effect, and heat of solution effect induced by the doped element M would collectively affect the Pt surface segregation energy in the Pt₃Ni/M (111) surfaces.     

Synergetic effects of impurities and alloying element Cr on oxidation and dissolution corrosion of Ni (111) surfaces: A DFT study

Using density-functional calculations, we studied the interactions between interstitial impurities (H, O, N, S, and P) and Ni (111) surfaces doped, or not, with Cr, and studied the effect of Cr doping on the dissolution corrosion resistance of Ni(111) surfaces. The aim of this work was to study, at the atomic scale, the effects of Cr on the segregation behaviors of impurities and the synergetic effects between co-doped atoms on the resistance to dissolution corrosion of Ni (111) surfaces. The results indicate that impurities S, P, O, and H prefer to be trapped at near-surface sites, that Cr was uniformly distributed in the Ni crystal and can affect the segregation behavior of impurities S and P to move toward the surface, and it affects impurities N and O such that they shift from the surface to the subsurface. The formation of near-surface Cr nitrides (speculated to be Cr₂N based on the results obtained for particular co-doped surfaces) was also noted. Introducing Cr enhances the structural stability of the Ni (111) surface and protects it from being corroded when impurities are present. The elementary processes studied afforded microscopic insights into the formation of a Cr-depleted zone, a phenomenon that leads to local corrosion of the Ni alloy surface. The results of our theoretical calculations explain some of the experimental results previously observed at the atomic scale.     

Temperature-programmed surface reaction (TPSR) of CH4 synthesis by PdxNi100−x nanoparticles

A series of Pd_xNi_100−x nanoparticles were prepared by the co-precipitation method and analyzed using a temperature-programmed surface reaction (TPSR) of their methanation reactions. ESCA measurement suggested that the as-prepared Pd-Ni alloys had Pd-core/Ni-shell structure. Surface Pd segregation occurred during H₂ reduction and resulted in a surface composition close to the nominal value. The TPSR experiments were performed by pre-adsorption of CO with H₂ to form methane. The peak temperature of methanation increased as Pd content increased, indicating that a methanation reaction is favored on Ni and Ni-rich alloy nanoparticles. For physical mixtures of Pd and Ni nanoparticles, methanation behaviors is similar to those of alloy nanoparticles; but the methanation temperatures of physical mixtures are always higher than those of alloy nanoparticles. This may be due to the formation of a Pd-enriched alloy surface layer during reduction in H₂ at 400 °C, or because the CO molecules adsorbed on the Pd sites spill over onto the Ni sites for methanation. Using TPSR technique and measuring methanation temperature, the top-most surface of such bimetallic nanoparticles can be probed.     

A model for oxidation-driven surface segregation and transport on Pt-alloys studied by atom probe tomography

Using a purpose-built 3D atom probe, we have previously shown that exposure to oxidising gases (NO, N₂O, O₂) induces Rh surface segregation in Pt–Rh alloys, the extent of which is strongly dependent on treatment temperature, crystallographic plane and the presence of ternary alloy additions. In this paper, the segregation trends identified on three different crystallographic surfaces of Pt–Rh are analysed using thermodynamic and kinetic arguments. The segregation model we present is generic for diffusion on alloy surfaces in the presence of active gases. From it we obtain activation energies and diffusion coefficients for the processes of metal-oxide species diffusion both perpendicular to and laterally across the surface. Using these we propose a simple model for the interaction of chemically active gases with the surfaces of such alloys. Applying this understanding to sequential oxidation/reduction treatments would in principle allow improved control of the surface composition of alloy catalysts. Related applications of this model include optimisation of core–shell catalyst nanoparticles.     

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：     

Calculation of chemisorption and absorption induced surface segregation

Using a pair bond type model for the interatomic interactions, we determine surface segregation on clean, H, O and CO covered surfaces of various alloys. Furthermore, we study surface segregation caused by bulk hydrogen absorption. Numerical results are presented for Pd_x Zr_1?x H_y We find, that strong surface segregation may result from chemisorption of O and CO and from absorption of H in the bulk of an alloy.     

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