Local effect of Na adsorption on Cu(111)

The local effect of Na adsorbed on Cu(111) at very low coverage is studied with the Density Functional Theory. We find that the Na atom and its three nearest neighbor Cu atoms tend to form a small cluster, with the Na effect on surface being localized. The Mulliken occupation, density of state, interatomic energy, and interorbital energy show that the electron transfer mainly occurs from the 2p and 3s orbitals of Na atom to the 3d and 4s orbitals of the nearest neighbor Cu atoms, with the formation of a bond with four components that have different energies. In the anti-bonding state region, the 2p state of Na plays a key role in the bond, while in the bonding state region, not only the 2p state of Na has a very significant contribution, but the 3s state (which is the outermost Na orbital) also contributes to the bond between Na and the Cu(111) surface.     

Bromine adsorption on Cu(111)

The dissociative chemisorption of molecular bromine on Cu(111) at 300 K has been studied using ultraviolet photoelectron spectroscopy (UPS), Auger electron spectroscopy (AES), low energy electron diffraction (LEED) and work function change measurements. A (√3 × √3)R30° structure is formed initially at a bromine coverage of 0.33 ML. This then converts to a (9√3 × 9√3)R30° compression structure with a coverage of 0.41 ML. The coincidence distance of the compression structure is determined entirely by the van der Waals diameter of adsorbed bromine. The applicability of using the van der Waals diameters of the three halogens, Cl, Br and I, to predict the saturation compression structures on Cu(111), is discussed.     

Oxygen adsorption on a Pd(111) surface

The interaction of oxygen with Pd(111) has been studied by means of AES, ELS, thermal desorption (TD), electron stimulated desorption (ESD) and work function measurements. It was found that a very small part ( ～ 2–3%) of the available adsorption sites are contributing to the O⁺ electron stimulated yield, the population of the latter being accompanied by enormously large work function changes (up to ～ 0.9 eV). A mechanism of adsorption and depopulation of these sites involving oxygen bulk and surface diffusion has been proposed.     

On the electronic surface band energy of the Cu(111)⧸Cs adsorption system

As Cs atoms are adsorbed, the electronic surface band of the Cu(111) surface is shifted towards lower energies. Good agreement with experiments is obtained by using a model which takes into account the relation between the surface state energy and the work function. Two other simple models are also discussed.     

Atomic adsorption of oxygen on Cu(111) and Cu(110)

We have studied angle-resolved inverse photoemission ( = 9.7 eV) after room temperature adsorption of oxygen on Cu(111) and Cu(110). On Cu(111) exposure to 500 L induces a band (3.0 eV aboveE _F at) which shows clear dispersion (1.0 eV) to higher energies for off normal incidence. Since no LEED superstructure is seen for that system, our results present strong evidence for the presence of short-range surface order. Two adsorbate bands are identified (2.8 eV and 6.3 eV at) on Cu(110)p(2×1)-O. Our results are in good agreement with a long-bridge adsorption site.     

Coverage dependent adsorption site for sulfur on Ni(111)

Angular-resolved photoemission spectra have been observed from two ordered sulfur overlayers, p(2×2) and (√3 ×√3)R30°, representing different coverages on the Ni(111) surface. Utilization of selection rules applicable to photoemission along the sample normal permits an assignment of placement and composition of the adsorbate induced bands. The spectra show dramatic changes in peak positions between these two overlayers similar in magnitude to those observed on Ni(100). The shifts in peak positions are attributed to symmetry prescribed changes in the surface unit cell relating to the character of the bond. Arguments that these changes provide evidence that the bonding site of the adsorbate atom may change with coverage are presented.     

Surface electronic structure of the Cu(111)/Na adsorption system

An ab initio calculation of the surface electronic structure of the Cu(111)/Na adsorption is presented. The results are consistent with (a) the bulk Cu band structure, (b) the known properties of the clean Cu(111) surface and (c) the extremely narrow and intense photoemission peak observed at E_F for adsorbed Na.     

Density functional study of the adsorption of K on the Cu(111) surface

The adsorption of potassium on the Cu(111) surface in a (2×2) pattern has been simulated with all-electron full-potential density functional calculations. The top site is found to be the preferred adsorption site, with the other highly symmetric adsorption sites being nearly degenerate. The bond length from potassium to the nearest copper atom is computed to be 2.83 ?. Population analysis and density of states indicate that there is no evidence for covalent bonding so that the binding mechanism appears to be a metallic bond. Received 11 April 2001     

Surface state energy shifts by molecular adsorption: CO ON Cu(111)

Molecular adsorption induced energy shifts of a surface state is observed for the Cu(111)/CO system. Angle resolved photoelectron energy spectra show that a zone center surface state shifts to higher energy relative to the Cu bulk bands. The effects is discussed in terms of charge transfer, molecular interaction range and absorption site.     

第一性原理研究氧在Ni(111)表面上的吸附能及功函数

采用基于密度泛函理论（DFT）广义梯度近似（GGA）下的第一性原理方法系统地研究了不同覆盖度下O在Ni（111）表面的吸附特性.计算结果表明,O在Ni（111）表面的稳定吸附位为三重面心立方（fcc）洞位,吸附能随着覆盖度的增加而减小,O诱导Ni（111）表面功函数的变化量与覆盖度成近线性关系,并随着覆盖度的增加而增大.同时,通过对电子密度和分波态密度的分析发现：O在Ni（111）表面的吸附使得Ni表面电子向O原子转移,形成表面偶极矩,导致功函数增加;表面Ni原子的3d轨道和O的2p轨道通过耦合、杂化作用形成成键态和反键态,而反键态几乎不被占据,因而O—Ni键相互作用比较强,吸附能较大. 关键词： 表面吸附 密度泛函理论 吸附能 功函数     

Ge adsorption on the Si(111) surface

Total energy calculations, performed for one monolayer of Ge adsorbed on Si(111), indicate that 1 × 1 models such as the atop site and hollow site adsorption geometries are unstable with respect to the formation of 2 × 1 Seiwatz chains of Ge adatoms. This result indicates that, for one monolayer coverage, Ge-Ge bonds are likely to form.     

The Tamm surface state on Cu(111) and Ag(111)

It is shown, that the well-known d-electron Tamm surface-state emission observed in photoelectron spectra from Cu(111) at the M̄ point in the surface Brillouin zone, is indeed due to such a surface state and not a bulk band transition as recently suggested L. Wallden, Solid State Commun. 59, 205 (1986). A similar surface state on Ag(111) is reported.     

Following local adsorption sites through a surface chemical reaction: CH3SH on Cu(111)

Studying the interaction of CH3SH, methanethiol, with Cu(111) as a model system, we demonstrate the ability of chemical-shift normal incidence x-ray standing wave field measurements to identify the local adsorption geometries of coadsorbed reaction products at different temperatures, a technical problem of broad chemical significance. In the present case the local geometries of four distinct S-containing adsorbate species (intact CH3SH, two thiolate (CH3S-) reaction intermediates and atomic S) are determined.     

Nonstochastic behavior of atomic surface diffusion on Cu(111) down to low temperatures

Atomic diffusion is usually understood as a succession of random, independent displacements of an adatom over the surface's potential energy landscape. Nevertheless, an analysis of molecular dynamics simulations of self-diffusion on Cu(111) demonstrates the existence of different types of correlations in the atomic jumps at all temperatures. Thus, the atomic displacements cannot be correctly described in terms of a random walk model. This fact has a profound impact on the determination and interpretation of diffusion coefficients and activation barriers.     

Surface layer relaxation on Mo(111) measured by low energy alkali ion scattering

The surface of clean Mo(111) has been studied using Li⁺ ion scattering at 1000 eV. The dependence of single scattering intensity was measured as a function of incident polar angle in the [12̄1] and the [21̄1̄] azimuths for various total scattering angles. Very pronounced intensity cut-offs are observed and are readily assignable to shadowing and blocking effects in scattering from first, second or third layer atoms. After taking certain precautions to avoid interference from deeper layers, the measured positions of the features yield the first-second layer spacing which is found to be strongly contracted by (18 ± 2)% compared to the bulk spacing. The method also indicates that the second-third layer spacing is possibly expanded (4 ± 4)%, but this result is uncertain due to possible contributions from deeper layers which make this value an upper limit of the layer spacing. The physical implications of these results and the uncertainties in the technique are discussed.     

Energy loss on of low energy ion N^＋q grazing the A1（111） surface

The total energy loss of N^＋q ions （for v 〈 Bohr velocity） grazing on the Al（111） has been simulated without any ＇fit＇ parameter and compared with the experimental data. The energy loss due to the charge exchange, happening before the N^＋q hits the Al（111） surface, is studied. The present simulation shows that the energy loss strongly depends on the charge state of the projectile and the lattice orientation of Al（111） surface. The calculated total energy loss agrees with experimental data very well.     

Triphenylene adsorption on Cu(111) and relevant graphene self-assembly

Investigations on adsorption behavior of triphenylene(TP) and subsequent graphene self-assembly on Cu(111) were carried out mainly by using scanning tunneling microscopy(STM).At monolayer coverage,TP molecules formed a longrange ordered adsorption structure on Cu(111) with an uniform orientation.Graphene self-assembly on the Cu(111) substrate with TP molecules as precursor was achieved by annealing the sample,and a large-scale graphene overlayer was successfully captured after the sample annealing up to 1000 K.Three different Moire patterns generated from relative rotational disorders between the graphene overlayer and the Cu(111) substrate were observed,one with 40 rotation between the graphene overlayer and the Cu(111) substrate with a periodicity of 2.93 nm,another with 70 rotation and 2.15 nm of the size of the Moire supercell,and the third with 100 rotation with a periodicity of 1.35 nm.