Investigation of the Au/Si (111) Surface Structures by X-Ray Diffraction

We have investigated the "5x1" and √3x√3R30° structures of Si(111) induced by adsorption of Au in the submonolayer regime. 52 and 13 symmetry-inequivalent structure factor intensities for reflections with fractional indices were measured for the "5x1" and the √3x√3 structures, respectively. Contour maps of the Patterson (autocorrelation) function show that in none of the structures are the Au-atoms situated on high-symmetry lattice sites, contrary to recently proposed models. A trimer model is deduced for the √3x√3 structure, whereas the "5x1" actually is a disordered 5x2 structure. We propose a model with two Au atoms per 5x1 subunit for this structure.