Kawasaki Mitsuo, Iino Masaki
Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Katsura, Kyoto 615-8510, Japan.
J Phys Chem B. 2006 Oct 26;110(42):21124-30. doi: 10.1021/jp0635213.
The self-assembly of ethanethiol (C(2)) and 1-octanethiol (C(8)) on Ag-Au(111) alloy films was studied by X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and scanning tunneling microscopy (STM), to illuminate how the monolayer structures and chemisorption-induced substrate defect structures depend on the alloy composition. The thiolate packing density at saturation increased approximately linearly with increasing Ag ratio. The CV data for reductive desorption of thiolates evidenced predominant or major contributions of Ag atoms to the substrate-sulfur interactions for the alloy surfaces. The STM study supported the lack of elemental periodicity on Ag-Au(111) and the consequent absence of periodicity in substrate-sulfur bonding. For C(8)-covered films, we observed systematic changes of substrate defect structures from elevated monatomic islands on Ag(111) to vacancy island structure on Au(111), in good correlation with the reductive desorption characteristics. The former type of defects can be explained best in terms of breakup of atomic terraces under excess thiolate packing density for Ag(111) and Ag-rich Ag-Au(111). As for the vacancy island formation, the present results are not agreeable with the chemical etching model but compatible with the lattice relaxation model.
通过X射线光电子能谱（XPS）、循环伏安法（CV）和扫描隧道显微镜（STM）研究了乙硫醇（C(2)）和1-辛硫醇（C(8)）在Ag-Au(111)合金薄膜上的自组装，以阐明单层结构和化学吸附诱导的基底缺陷结构如何依赖于合金组成。饱和时硫醇盐的堆积密度随Ag比例的增加近似呈线性增加。硫醇盐还原解吸的CV数据证明，对于合金表面，Ag原子对基底-硫相互作用起主要或重要作用。STM研究支持了Ag-Au(111)上缺乏元素周期性以及基底-硫键合中相应缺乏周期性的观点。对于覆盖C(8)的薄膜，我们观察到基底缺陷结构从Ag(111)上凸起的单原子岛到Au(111)上的空位岛结构的系统变化，这与还原解吸特性密切相关。前一种类型的缺陷可以最好地用Ag(111)和富Ag的Ag-Au(111)在硫醇盐堆积密度过高时原子台阶的破裂来解释。至于空位岛的形成，目前的结果与化学蚀刻模型不一致，但与晶格弛豫模型相符。
