X-ray photoelectron diffraction study of the structures of W(001)c(2 × 2)-Au and -Ag surfaces

Abstract

We have applied XPD (X-ray photoelectron diffraction) to the surfaces of W(001)c(2 × 2)-Au and -Ag. Au4f and Ag3d XPD patterns have been measured for the two c(2 × 2) surfaces at electron take-off angles of 4°–22°. It is found that both Au 4f and Ag 3d XPD patterns are very similar to each other showing that the two surfaces have essentially the same structure. Consideration of the general properties of XPD, coverage and bond-lengths of the constituent atoms led to two plausible models (surface-alloy and overlayer models) for the surfaces. We have tested the two models by kinematical analyses of the XPD patterns for the W(001)c(2 × 2)-Au surface using either an s-symmetry and spherical-wave formula or a formula with spherical and dipole-selected final states. It has turned out that although the surface-alloy model is more plausible, the kinematical calculations for the two models do not reproduce the details of the experiment indicating the importance of multiple scattering of electrons for these surfaces consisting of high- Z atoms.