铝和银在铱（111）宽范围吸附的稳定性、原子构型及电子特性研究

利用第一性原理密度泛函理论研究了铝和银在铱的111面的宽范围吸附特性。基于密度泛函理论计算了覆盖度在0.11ML到2.00ML的结构稳定性、原子构型及平均结合能。对于铝原子在铱111面的吸附,最稳定的结构是铝原子覆盖度为0.5ML位于密堆六方空位（hcp-hollow）,相应的结合能为-4.68eV;对于亚层铝原子的吸附,最稳定结构是铝原子覆盖度为1.00ML时位于octahedral位置,相应的结合能为-5.28eV。对于覆盖度为2.00ML的满覆盖度混合结构的表层及亚层吸附,最稳定结构是Al位于六方密堆及八方密堆位置,相应的结合能为-4.70eV。这意味着当铝原子以满覆盖度吸附在铱的111面上时,趋向于在铱的111面的亚层形成化学键,而非吸附于表层。相比于铝吸附在铱111面,银的吸附特性呈现出很大的不同,面心位置更为稳定,在覆盖度为0.25ML时其结合能为3.89eV,略微高出密堆六方位置处3.88eV的结合能。     

铝和银在铱(111)宽范围吸附的稳定性、原子构型及电子特性研究（英文）

利用第一性原理密度泛函理论研究了铝和银在铱的111面的宽范围吸附特性.基于密度泛函理论计算了覆盖度在0.11 ML到2.00 ML的结构稳定性、原子构型及平均结合能.对于铝原子在铱111面的吸附,最稳定的结构是铝原子覆盖度为0.5 ML位于密堆六方空位(hcp-hollow),相应的结合能为-4.68 e V;对于亚层铝原子的吸附,最稳定结构是铝原子覆盖度为1.00 ML时位于octahedral位置,相应的结合能为-5.28 e V.对于覆盖度为2.00 ML的满覆盖度混合结构的表层及亚层吸附,最稳定结构是Al位于六方密堆及八方密堆位置,相应的结合能为-4.70 e V.这意味着当铝原子以满覆盖度吸附在铱的111面上时,趋向于在铱的111面的亚层形成化学键,而非吸附于表层.相比于铝吸附在铱111面,银的吸附特性呈现出很大的不同,面心位置更为稳定,在覆盖度为0.25 ML时其结合能为3.89 e V,略微高出密堆六方位置处3.88 e V的结合能.     

氯原子在Cu(111)表面的吸附结构和电子态

密度泛函理论(DFT)总能计算研究了不同覆盖度下氯原子在Cu(111)表面的吸附结构和表面电子态。计算结果表明,清洁Cu(111)表面自由能 为15.72 ,表面功函数φ为4.753eV。在1/4ML和1/3ML覆盖度下,每个氯原子在Cu(111)表面fcc谷位的吸附能分别等于3.278eV/atom和3.284eV/atom。在1/2ML覆盖度下,两个紧邻氯原子分别吸附于fcc和hcp谷位,氯原子的平均吸附能为2.631eV/atom。在1/3ML覆盖度下,fcc和hcp两个位置每个氯原子吸附能的差值约为2meV/atom,与正入射X光驻波实验结合蒙特卡罗方法得到结果(<10meV/atom)基本一致。在1/4ML、1/3ML和1/2ML覆盖度下,吸附后Cu(111)表面的功函数依次为5.263eV、5.275eV和5.851eV。吸附原子和衬底价轨道杂化形成的局域表面电子态位于费米能级以下约1.2eV、3.6eV和4.5eV等处。吸附能和电子结构的计算结果表明,氯原子间的直接作用和表面铜原子紧邻氯原子数目是决定表面结构的两个重要因素。     

Cl原子在γ-TiAl(111)表面吸附的第一性原理研究

基于密度泛函理论,在广义梯度近似下研究了Cl在γ-TiAl(111)表面的吸附.计算结果表明:γ-TiAl(111)表面的面心立方位置(fcc)和六角密排位置(hcp)为Cl吸附的稳定位置,当覆盖度Θ小于一个单层(ML)时,Cl原子倾向于吸附在γ-TiAl(111)表面近邻为多Ti的位置.电子结构分析发现,Cl原子同表面金属原子形成较强的离子键,并且成键具有一定的方向性.当Cl原子和O原子共同在γ-TiAl(111)表面吸附时,二者都趋     

Al吸附在Pt,Ir和Au的(111)面的低覆盖度研究

应用密度泛函理论,系统研究了Al原子在Pt(111),Ir(111)和Au(111)表面的桥位、顶位、三重面心立方(fcc)洞位和六角密排(hcp)洞位这四个典型位置的吸附情况. 主要计算了三吸附体系的几何结构、平均结合能和差分电荷密度,并系统讨论了相关原子的密立根电荷布居数和投影态密度.研究发现,对于Pt(111)和Ir(111)表面,Al原子在hcp洞位最稳定,但是对于Au(111)表面,Al原子在fcc洞位最稳定. 关键词： 吸附 密度泛函理论 结合能 电子结构     

覆盖度对S原子在Ir(001)表面吸附性质的影响

采用第一性原理方法模拟了覆盖度对S原子在Ir(001)表面吸附能和电子结构的影响。结果表明：在覆盖度0.50 ML以下,S原子吸附在Hollow空位最稳定,且吸附能几乎不随覆盖度变化;在覆盖度0.66 ML以上吸附能随覆盖度增加而减小。吸附体系金属表面d带电子结构随覆盖度变化与O/Pt(111)吸附体系相似。这些结果与Hammer-Nørskov模型吻合。     

O在Au(111)表面吸附的密度泛函理论研究

应用密度泛函理论，本文系统地研究了O在Au(111)表面上的吸附能、吸附结构、功函数、电子密度和投影态密度，给出了覆盖度从0.11ML到1.0ML的范围内，O的吸附特性随覆盖度变化的规律.研究发现O的稳定吸附位为3重面心立方(fcc)洞位，O在fcc洞位的吸附能对覆盖度比较敏感，其值随着覆盖度的增加而减小；O诱导Au(111)表面功函数的变化量与覆盖度成近线性关系，原因是Au表面电子向O偏移，形成表面偶极子；O—Au的相互作用形成成键态和反键态，且反键态都被占据，造成O—Au键很弱，O吸附能较小. 关键词： 表面吸附 Au(111)表面 密度泛函理论 电子特性     

覆盖度对S原子在Ir(001)表面吸附性质的影响

采用第一性原理方法模拟了覆盖度对S原子在Ir(001)表面吸附能和电子结构的影响。结果表明：在覆盖度0.50 ML以下，S原子吸附在Hollow空位最稳定，且吸附能几乎不随覆盖度变化；在覆盖度0.66 ML以上吸附能随覆盖度增加而减小。吸附体系金属表面d带电子结构随覆盖度变化与O/Pt(111)吸附体系相似。这些结果与Hammer-Nørskov模型吻合。     

H2S在Fe(100)面吸附的第一性原理研究

基于密度泛函理论第一性原理, 在广义梯度近似下, 研究了表面覆盖度为0.25 ML (monolayer)时硫化氢分子在Fe(100)面吸附的结构和电子性质, 并与单个硫原子吸附结果进行了对比. 结果表明: 硫化氢分子吸附在B2位吸附能最小为-1.23 eV, 最稳定, B1位吸附能最大为-0.01 eV, 最不稳定; 并对硫化氢分子在B1位和B2位吸附后的电子态密度进行了分析, 也表明了吸附在B2位稳定, 且吸附在B2位后硫化氢分子几何结构变化不大; 将硫化氢中硫原子吸附与单个硫原子吸附的电子性质进行了比较, 发现前者吸附作用非常微弱; 同时对吸附后的Fe(100)面进行了对比, 单个硫原子吸附的Fe(100)面电子态密度出现了一系列峰值且离散分布, 生成了硫化亚铁, 表明在硫化氢环境下, 主要是硫化氢析出的硫原子发生了吸附. 关键词： 第一性原理 Fe(100)表面 吸附能 硫化氢     

S在Cu(111)表面吸附的第一性原理研究*

基于广义梯度近似的投影缀加平面波(Projector augmented wave) 赝势和具有三维周期性边界条件的超晶胞模型,采用第一原理方法计算并分析了由于S吸附所形成的S/Cu(111)界面体系的吸附结构、吸附能和局域电子结构,考虑了不同覆盖度（1,0.25ML）下S在不同吸附位置的吸附特性. 结果表明：S原子倾向于吸附在高对称的fcc位与hcp位;由于S的负电性而使S/Cu吸附能随覆盖度的减小而增加, 与之相应,S-Cu键长随覆盖度的减小而缩短. DOS图、Bader电荷分析表明杂化主要发生在S的3p态和表面Cu原子的3d态之间,表层近邻的Cu原子向S转移的电子数随覆盖度增加而减小,这表明S与Cu(111)面有强的相互作用.     

Ar adsorptions on Al (111) and Ir (111) surfaces: a first-principles study

We investigate the adsorptions of Ar on Al (111) and Ir (111) surfaces at the four high symmetry sites, i.e., top, bridge, fcc- and hcp-hollow sites at the coverage of 0.25 monolayer (ML) using the density functional theory within the generalized gradient approximation of Perdew, Burke and Ernzerhof functions. The geometric structures, the binding energies, the electronic properties of argon atoms adsorbed on Al (111) and Ir (111) surfaces, the difference in electron density between on the Al (111) surface and on the Ir (111) surface and the total density of states are calculated. Our studies indicate that the most stable adsorption site of Ar on the Al (111) surface is found to be the fcc-hollow site for the (2 × 2) structure. The corresponding binding energy of an argon atom at this site is 0.538 eV/Ar atom at a coverage of 0.25 ML. For the Ar adsorption on Ir (111) surface at the same coverage, the most favourable site is the hcp-hollow site, with a corresponding binding energy of 0.493 eV. The total density of states (TDOS) is analysed for Ar adsorption on Al (111) surface and it is concluded that the adsorption behaviour is dominated by the interaction between 3s, 3p orbits of Ar atom and the 3p orbit of the base Al metal and the formation of sp hybrid orbital. For Ar adsorption on Ir (111) surface, the conclusion is that the main interaction in the process of Ar adsorption on Ir (111) surface comes from the 3s and 3p orbits of argon atom and 5d orbit of Ir atom.     

Interaction of silver atoms with iridium and with a two-dimensional graphite film on iridium: Adsorption,desorption, and dissolution

The initial stages in the interaction of silver with the (111)Ir surface and with a two-dimensional graphite film (2D GF) on (111)Ir were studied by high-resolution electron Auger spectroscopy in ultrahigh vacuum. The growth mechanisms of silver films and the desorption fluxes of Ag atoms were determined, and their desorption energies estimated. It was found that the Ag desorption fluxes from a 2D GF on Ir and from a thick silver film on the pure metal are similar and considerably (an order of magnitude) smaller than the sublimation fluxes from bulk silver at the same temperatures. The activation energy for desorption from a submonolayer film varies from 3.2 eV for coverage θ=1 to 3.7 eV at θ ～ 0. It was shown that silver atoms do not penetrate into the substrate bulk throughout the temperature range covered (300–1800 K).     

Energetics of oxygen embedment into unreconstructed and reconstructed Cu(1 0 0) surfaces: Density functional theory calculations

Atomic oxygen embedment into a Cu(1 0 0) surface is studied by density functional theory calculation and the nudged elastic band method. As the oxygen coverage increases on the unreconstructed surface from 0.25 monolayer (ML) to 0.75 ML, the energy barrier for oxygen embedment decreases and an energetically favorable sub-surface site is found at 0.75 ML coverage. At a fixed oxygen coverage of 0.5 ML, the oxygen embedment energetics vary with the surface morphology and the embedment is found to be more probable for reconstructed structures compared to the bare surface. On the missing-row reconstructed surface, we find that the energy barrier for atomic oxygen embedment is smaller through the missing-row compared to other paths, suggesting a mechanism for the formation of sub-surface oxygen structures that are consistent with a recent experiment. The energy barrier for sub-surface oxygen diffusion is predicted to be less than that for on-surface diffusion.     

The growth mode of aluminium on silver (111)

The geometric and electronic structures occuring during the growth of Al on a single crystal Ag(111) surface have been studied using a combination of low energy electron diffraction (LEED), Auger electron spectroscopy (AES), energy loss spectroscopy (ELS) and work function measurements. The Auger signal versus deposition time plots, which were used to monitor the growth mode, are shown to behave in an identical fashion to that expected for layer-by-layer (Frank-van der Merwe) growth. LEED was used to determine the lateral periodicity of thin Al films and shows that Al forms, at very small coverages, 2D islands which have the same structure as the Ag(111) substrate and which grow together to form the first monolayer. At substrate temperatures of 150 K a well defined (1 × 1) structure with the same orientation as the underlying Ag(111) can be seen up to at least 12 ML. After completion of the third monolayer the ELS spectrum approached that observed for bulk aluminium. At a coverage of 3 ML the work function decreases by 0.4 eV from the clean silver value.     

Atomic oxygen adsorption on Pb(1 0 0)

We study atomic oxygen adsorption on a Pb(1 0 0) surface using density functional theory. The structures, binding energies, work function, and charge transfer of on-surface and subsurface adsorption are investigated at a range of coverages from 0.06 to 1.00 ML. The energetically favored adsorption site for on-surface adsorption is found to be a distorted hollow site for the whole coverage range studied. The distorted structures are stabilized by mixing of 6s and 6p states of lead mediated by the 2p states of oxygen. For subsurface adsorption, the sub-bridge site is found to be preferred to the sub-hollow site at low coverages, the two being nearly equal in energy at monolayer coverage. At 0.11 ML coverage, diffusion from an on-surface hollow site to a sub-bridge site is found to be barrierless, suggesting facile subsurface oxidation at low coverages. Combined on-surface and subsurface adsorption leads to the formation of a two-layer oxide structure resembling β-PbO.     

On-surface and sub-surface oxygen on ideal and reconstructed Cu(1 0 0)

In order to understand the first steps of the Cu(1 0 0) oxidation we performed first principles calculations for on-surface and sub-surface oxygen on this surface. According to our calculations, the adsorption energies for all on-surface site oxygen atoms increase, whereas the energies of the sub-surface atoms decrease with the increasing oxygen coverage. At coverage 1 ML and higher on the reconstructed surface, structures including both on- and sub-surface atoms are energetically more favourable than structures consisting only of on-surface adsorbates. On the ideal (1 0 0) surface this change can be perceived at coverage 0.75 ML.     

Electronic structure and ordering of multilayers of Co and Ag on Cu(111) investigated by photoelectron spectroscopy

The growth and the electronic structure of multilayers of Co and Ag on Cu(111) at room temperature have been studied with photoelectron spectroscopy and low-energy electron diffraction (LEED). The coverage range spans from Co and Ag layers between one monolayer (ML) to stacking of several monolayers. Surface states and ordered structures have been identified at room temperature. A Ag-related surface state with a binding energy of 0.30 eV is identified in normal emission in the ultraviolet photoelectron spectra when silver constitutes the top layer. Core-level binding energy shifts of Ag 3d_5/2 reflect the changing surroundings of Ag. Hexagonal diffraction patterns are observed for sandwiches of consecutive layers of Co and Ag up to 5 layers. Since no interlayer diffusion is observed in the layer-by-layer formation of the films, multilayers of consecutive silver and cobalt on Cu(111) offer preparation of sandwiched magnetic–non-magnetic structures.     

XPS studies of adatom-adatom interactions: I/Ag(111) and I/Cu(111)

We have studied submonolayer adsorption, at room temperature, of iodine on the (111) faces of silver and copper, using LEED and XPS. In both systems the √3 × √3 LEED pattern appears at ～0.2 monolayer (ML) coverage; no other superlattice pattern was observed. The $\text{I}\text{4}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ core electron binding energy in both cases decreases by ～0.15 eV between very dilute coverage and 0.33 ML. The leveling-off of the binding energy for I/Ag(111) for coverages >0.2 ML is shown to be a unique experimental manifestation of an indirect, substrate-mediated adatom-adatom interaction, an attraction of several meV between next-nearest neighbor iodine atoms. The more nearly linear decrease in the I binding energy on Cu(111) is shown to imply a significantly weaker next-nearest neighbor interaction on this surface. The appearance of the √3 × √3 LEED pattern at low coverages on Cu is shown to be consistent with short-range order produced merely by a size effect, that is, by nearest neighbor exclusion. These conclusions are reached with the help of Monte Carlo calculations of a triangular lattice gas.     

甲基和羟基在Ir(111)表面吸附的密度泛函理论研究

在超原胞近似和slab模型基础上,采用周期性密度泛函理论,在0.11覆盖度（ML）下,对甲基与羟基在Ir(111)表面的吸附进行了研究,得到了甲基和羟基在Ir(111)表面不同吸附位置的吸附能和吸附构型,计算了它们的振动频率,同时分析了甲基和羟基共吸附于Ir(111)表面的情况。结果表明,甲基和羟基在Ir(111)表面的最稳定吸附位置都是top位,甲基是碳端向下吸附,羟基是通过氧端向下倾斜吸附。通过频率分析发现吸附后CH3中C-H键的对称伸缩振动、反对称伸缩振动以及剪切振动频率均发生了红移,而羟基中的O-H键的振动频率发生蓝移现象。通过计算对比发现甲醇分解为甲基和羟基过程是一个放热反应,从热力学角度来说该反应是可行的。