Alkali adsorption on the Al(001) surface

The chemisorption of Na on the Al(001) surface has been studied by 2D bandstructure calculations on slab models using a density functional STO-LCAO method. Two slab models of three and five layers of substrate atoms have been used. Overlayers of the structuresp(2×2),c(2×2) andp(1×1), representing coverages of a quarter, a half and a full atomic monolayer of sodium atoms, respectively, have been investigated. The electronic structure of the adatoms and the charge transfer to the substrate are discussed. Satisfactory agreement with experiment is obtained for the adsorption induced change of the work function, correctly reproducing its monotonic character.     

Structure of ultra-thin Ti film on the Al(001) surface

The atomic structure of sub-monolayer amounts of Ti deposited on the Al(001) surface at room temperature has been investigated using low-energy electron diffraction (LEED) and low-energy ion scattering spectroscopy (LEIS). The Ti coverage was determined using Rutherford backscattering spectroscopy (RBS). Though a crisp LEED image is inherently difficult to obtain, the symmetry of the observed c(2 × 2) LEED images allows us to infer a structure which places Ti atoms in every other Al lattice site. Analysis of the LEIS azimuth- and polar-angle scan spectra has been done to determine the best structural model which supports the c(2 × 2) symmetry of the LEED image as well as LEIS experimental data. It was concluded that the best model consistent with the experimental data, puts Ti preferentially below the surface of the Al substrate at every other lattice site for sub-monolayer coverage of Ti on Al(001). As Ti coverage increases, the presence if Ti atoms in the surface layer also increases. Results of this study are relevant to research pertaining to the possible use of Ti as a catalyst in sodium alanate (NaAlH₄) in hydrogen storage applications.     

In在Al(001)表面偏析的模拟

通过一种空位模型详细的描述了In在Al(001)表面的扩散偏析过程,利用周期性密度泛函理论方法计算了这个偏析过程中每步构型的能量和In原子扩散的能量壁垒,并对可能的偏析机理进行分析.结果表明:In原子从Al(001)表面第二层扩散偏析至表面层时,系统的能量降低了0.64 eV,最大的扩散迁移壁垒为0.34 eV;而从表面更内层向表面第二层扩散时系统能量基本保持不变,扩散需要克服的能量壁垒为0.65 eV,说明In原子在Al(001)表面只能由体内向表面扩散偏析.In在Al(001)的清洁表面具有强烈的偏析趋势,在热力学上是容易进行的. 关键词： 密度泛函理论 表面偏析 扩散 Al合金     

A DFT study of substrate effect on the magnetism of V(001) surface

The effect of isoelectric transition metals (TM) Nb and Ta on the magnetism of the V(001) surface is investigated from first principles using Density functional theory (DFT), with the generalized gradient approximation (GGA). Ferromagnetic (FM) moments of 2.5 μ_B and 2.2 μ_B are obtained for the relaxed surface V monolayer (ML) in the V/Nb(001) and the V/Ta(001) systems respectively, at T = 0 K. The values are almost twice of those obtained with Mo and W of group VIB and can be attributed to the comparatively smaller bandwidths of the substrates Nb and Ta. Small induced magnetic moments are present on the Nb and Ta interfacial layers, which are coupled anti-ferromagnetically with the V ML.     

Dynamic structure mediated by graphitelike Al nets on the Al2Cu (001) surface

A detailed study of the (001) surface of the Al(2)Cu crystal using both experimental and ab initio computational methods is presented in this work. The combination of both approaches gives many arguments to match the surface plane with a bulk truncated surface model terminated by incomplete Al planes. The missing rows of Al atoms lead to a 2√2×√2R 45° surface reconstruction with two domains rotated by 90° from each other. Ab initio calculations demonstrate that the energetic cost associated with the removal of pairs of Al atoms is the lowest for the two nearest surface Al atoms (covalentlike interaction). They reveal that the remaining atomic rows of various widths are oriented according to the graphitelike Al 6(3) nets used to describe the Al(2)Cu bulk structure. The surface dynamics observed at 300 K at the Al(2)Cu surface is also presented. Finally, configurational and vibrational entropies are introduced to discuss the reduced surface plane density.     

Fabrication and modification of the supported Al nanoparticles on the Al(001) and (110) surfaces using the reversible vertical single-atom manipulation with the Cu and Pt trimer-apex tips: a first-principles study

First-principles simulations show that at the step edge of the stepped Al(001) and (110) surfaces and at the edge of the small supported nanoparticles like the dimer, trimer, and tetramer, single Al atoms can be extracted and repositioned using the Cu trimer-apex tip and the Pt tip of a Al apex, while a more weakly adsorbed single Al adatom on the plane terrace of the flat surface or of the nanocluster cannot be vertically picked up by these two tips. This result suggests in principle a non-electrically assisted method of fabricating and modifying metal nanoparticles at the atomic scale using the vertical single-atom manipulation. As an illustration, a pyramidal nanocluster of five Al atoms is assembled on the Al(001) surface in an atom-by-atom way with the Cu trimer-apex tip, moreover, it can be modified to be two-dimensional in shape.     

AB initio hartree-fock study of the MgO(001) surface

The MgO(001) surface has been studied with an ab initio Hartree-Fock crystalline orbital LCAO program. An optimized basis set containing nine atomic orbitals (three s and six p) per atom has been used. The semi-infinite crystal has been simulated by a slab containing three planes (six atoms per cell). In agreement with the most recent LEED experiments, no relaxation is found and the “rumpling” is very small (1% of the nearest neighbour separation in the bulk). The analysis of the electron charge distribution and of the ion multipoles shows that the fully ionic character found for the bulk is maintained at the surface, and that the anion deformation is very small. A surface energy of 1.43 J/m² was obtained.     

氢吸附金刚石（001）表面的第一性原理研究

采用第一性原理方法研究氢吸附的金刚石（001）表面，计算了氢吸附金刚石表面构型.通过分析吸附前后空间电荷分布的变化，发现吸附H原子的金刚石（001）表面电荷向H原子转移，即表明氢吸附的金刚石表面带负电.分析了这种现象的微观机制，以及它对金刚石表面电学性质的影响. 关键词： 第一性原理计算 金刚石（001）面 表面吸附 电荷密度分布     

Experimental study of surface and bulk plasmon losses induced in Al(001) by low energy electrons

We have measured the relative intensity of the elastic peak, and of the surface and bulk plasmon loss peaks, for electrons backscattered from an Al(001) single crystal surface. The exciting beam has an energy between 100 and 2000 eV, and impiges on the surface in an high symmetry plane of incidence with a colatitude angle of incidence varying between 0° and 80°. In a first series of experiments called “angle integrated experiment”, all the backscattered electrons are collected in a 2π solid angle retarding field analyser as a function of the primary beam energy and colatitude angle of incidence. In a second series called “angle resolved experiment”, the acceptance angle of the detector is set at 10° or $\text{1}\text{2}\text{°}$ and the variable parameters are colatitude angles of incidence and emission. We observe mainly that very clean aluminum exhibits large plasmon loss peaks with a negligible background. The results cannot be accounted for without sophisticated models, but “angular resolved experiments” are more suitable for a simple discussion than the “angle integrated experiment” and show mainly the phonon-plasmon coupling plus a θ dependent creation probability.     

Si(001)表面In量子线的第一原理研究

利用第一原理理论研究了金属In在Si(001)表面吸附的原子结构.结果表明,In原子的吸附不破坏衬底Si的二聚体化学键.在低覆盖率时,In原子在Si(001)衬底上形成有序量子线,取向沿衬底Si的二聚体化学键方向.计算结果显示相邻In线之间不存在排斥作用.     

InAs(001)表面脱氧动力学分析

利用反射式高能电子衍射(RHEED)实时监控对InAs衬底进行两步完全脱氧的过程, 对比了有低(高)砷等效束流压强保护下采用两步法对InAs衬底缓慢长时间的高温脱氧过程. InAs衬底两步完全脱氧法的第一步为传统的缓慢升温脱氧方法, 第二步为高温In束流辅助脱氧方法. 衬底高温脱氧的RHEED衍射图样说明了高温In束流辅助脱氧最终完全清除传统的缓慢升温法无法去掉的残留氧化物, 通过脱氧完成同质外延生长后的扫描隧道显微镜图像, 说明高砷等效束流压强保护下的脱氧方法是可行的; 分析了高温In束流能完全清除衬底表面残余In氧化物的原理. 关键词： 热分解 Ⅲ-V族半导体 反射式高能电子衍射     

Vacancy diffusion in the Cu(001) surface I: an STM study

We have used the indium/copper surface alloy to study the dynamics of surface vacancies on the Cu(0 0 1) surface. Individual indium atoms that are embedded within the first layer of the crystal, are used as probes to detect the rapid diffusion of surface vacancies. STM measurements show that these indium atoms make multi-lattice-spacing jumps separated by long time intervals. Temperature dependent waiting time distributions show that the creation and diffusion of thermal vacancies form an Arrhenius type process with individual long jumps being caused by one vacancy only. The length of the long jumps is shown to depend on the specific location of the indium atom and is directly related to the lifetime of vacancies at these sites on the surface. This observation is used to expose the role of step edges as emitting and absorbing boundaries for vacancies.     

Phosphine dissociation on the Si(001) surface

Density functional calculations are performed to identify features observed in STM experiments after phosphine (PH3) dosing of the Si(001) surface. On the basis of a comprehensive survey of possible structures, energetics, and simulated STM images, three prominent STM features are assigned to structures containing surface bound PH2, PH, and P, respectively. Collectively, the assigned features outline for the first time a detailed mechanism of PH3 dissociation and P incorporation on Si(001).     

First-principles molecular dynamics study of acetylene adsorption on the Si(001) surface

We present a first-principles molecular dynamics study of acetylene adsorption on the Si(001) surface. Acetylene molecules are di-σ bonded to the first layer Si dimers with the adsorption energy of 64.8 kcal/mol. It is elucidated that the CC bond is essentially double bond and the Si dimer bonds are not cleaved. The normal mode analyses well reproduce the experimental results, giving a strong support to our results.