DYNAMICAL ANALYSIS OF X-RAY PHOTOELECTRON DIFFRACTION FROM W(001)c(2×2)-Ag AND -Au SURFACES

Abstract

The local structures of W (001) c (2×2)- Ag and - Au [refer to as c (2×2)- Ag and - Au ] surfaces have been studied by x-ray photoelectron diffraction (XPD) for Ag-3d and Au-4f emissions with both multiple-scattering and single-scattering cluster approaches. Our dynamical study has revealed that the outermost layers of these surfaces form rumpled alloy structures, and the height of adsorbate atoms is 0.3±0.1 Å above that of W atoms in the top layer, and both adsorbate and tungsten atoms are at fourfold symmetric sites on the surfaces. It is also found in this study that there is a strong multiple-scattering effect on these surfaces, and a kinematical analysis fails completely on XPD from the c (2×2)- Ag surface at a high kinetic energy of 1115 eV, where the validity of the single-scattering theory was taken for granted in the past. Conditions that may result in such a strong multiple scattering in the systems are discussed in this paper.