Xiao H Y, Zu X T, Zhang Y F, Yang L
Department of Applied Physics, University of Electronic Science and Technology of China, Chengdu.
J Chem Phys. 2005 May 1;122(17):174704. doi: 10.1063/1.1886733.
First-principles calculations based on density functional theory-generalized gradient approximation method have been performed on cesium adsorption on Si(001)(2 x 1) surface. The optimized geometries and adsorption energies have been obtained and the preferred binding sites have been determined for the coverage (Theta) of one monolayer and half a monolayer. At Theta = 0.5 ML the most stable adsorption site is shown to be T3 site. At Theta = 1 ML two Cs atoms are adsorbed at HH and T3 sites, respectively. It was found that the saturation coverage of Cs for the Si(001)(2 x 1)-Cs surface is one monolayer instead of half a monolayer. This finding supports the majority of experimental observations but does not support recent coaxial impact collision ion scattering spectroscopy investigations [Surf. Sci. 531, L340 (2003)] and He(+) Rutherford backscattering spectroscopy studies [Phys. Rev. B 62, 4545 (2000)]. Mulliken charge and overlap population analysis showed that the Cs-Si bond is indeed ionic rather than polarized covalent as generally assumed for alkali metal (AM) on Si(001)(2 x 1) surface. Geometrical structure analysis seems to have limitations in determining the nature of AM-substrate bond. We also found that the silicon surface is metallic and semiconducting for the coverages of 0.5 and 1 ML, respectively.
基于密度泛函理论-广义梯度近似方法进行了第一性原理计算，研究了铯在Si(001)(2×1)表面的吸附情况。得到了优化的几何结构和吸附能，并确定了单层覆盖度（Theta）和半层覆盖度下的优先结合位点。在Theta = 0.5 ML时，最稳定的吸附位点是T3位点。在Theta = 1 ML时，两个Cs原子分别吸附在HH和T3位点。研究发现，Si(001)(2×1)-Cs表面Cs的饱和覆盖度是单层而非半层。这一发现支持了大多数实验观察结果，但不支持最近的同轴碰撞离子散射光谱研究[《表面科学》531, L340 (2003)]和He(+)卢瑟福背散射光谱研究[《物理评论B》62, 4545 (2000)]。穆利肯电荷和重叠布居分析表明，Cs-Si键实际上是离子键，而不是像通常认为的碱金属（AM）在Si(001)(2×1)表面那样是极化共价键。几何结构分析在确定AM-衬底键的性质方面似乎存在局限性。我们还发现，对于覆盖度为0.5 ML和1 ML的情况，硅表面分别呈现金属性和半导体性。
