Au(111)面甲烷硫醇吸附的密度泛函理论研究

Density Functional Theory Studies on the Adsorption of Methane-thiol Molecule on Au(111) Surface

采用基于密度泛函理论的第一性原理方法和平板模型研究了CH3SH分子在Au(111)表面的吸附构型和电子结构.系统地计算了S原子在不同位置以不同方式吸附的系列构型,计算结果表明,CH3SH分子倾向于吸附在top位上,S—C键相对于Au表面法线的夹角为62°～78°;而S—H键断裂后CH3S_H则倾向于吸附在bri-fcc位上,S—C键相对于Au(111)表面法线的夹角为49°～57°.比较分析CH3SH分子和CH3S_H的吸附,发现CH3SH分子倾向于不解离吸附,表面温度的提升和缺陷的出现可能促使S—H键的断裂.通过比较S原子在独立的CH3SH分子和吸附状态下的局域态密度,发现S—H键断裂后S原子和表面的键合强于S—H键未断裂时S原子和表面的键合.扫描隧道显微镜(STM)图像模拟显示了CH3SH和CH3S_H在Au(111)表面吸附的3个典型的STM图像.

By using the first-principles method based on density functional theory and slab model, the atomic geometries and electronic structures for the adsorptions of methane-thiol molecule on Au（111） surface were studied. A series of possible adsorption configurations constructing by S atom on different site with different orientation were studied. The adsorption energies indicate that most of the CH3SH molecules prefer to adsorb on the top site, and the tilt angle is around 62°-78°; while most of the dissociated CH3S_H prefer to adsorb on bri-fcc site, and the tilt angle is around 49°-57°. The comparisons between the nodisso- ciative and dissociative adsorption show that CH3SH prefer nodissociative adsorption on the Au（111） surface, the increase of the surface temperature and defect may make the S-H bond break. It is indicated that the bonding between S atom and substrate is much stronger in the dissociated adsorption by comparing the local density of states of S atom between the single CH3SH and the adsorbed molecule, also the dissociated CH3S_H. Our STM （scanning tunneling microscopy） simulations show us three distinctive pattern for the adsorption of CH3SH and CH3S_H on Au（111） surface.