Structural study of Si(1 1 1)21×21-(Ag+Au) surface by X-ray diffraction

The in-plane structure of Si(1 1 1)21×21-(Ag+Au) surface was studied by using grazing incidence X-ray diffraction method. A total of 72 inequivalent fractional order reflections were obtained. The structural models are investigated including the previously proposed models. It is found that the Ag triangles and Si trimers are induced to displace considerably from the honeycomb chained triangle arrangement by the adsorption of Au atoms. From the analysis, the models with five Au atoms in the unit cell, which have the Au–Au interatomic distance peculiar to the 21×21 periodicity, are favored.