A scanned-angle and scanned-energy photoelectron diffraction study of (√3 × √3) R30° Ag on Si(111)

Abstract Photoelectron diffraction data for Ag3d emission from ( 3 × 3 R 30° Ag on Si(111) have been obtained in all three possible modes: scanned polar angle, scanned azimuthal angle, and scanned energy. Single and multiple scattering cluster calculations with spherical-wave scattering have been carried out for a wide range of structural models and compared to experiment using R factors. In addition, scanned-angle photoelectron diffraction data for the substrate Si 2p intensities have been obtained over essentially the full solid angle above both the clean and Ag-covered surfaces. These data and their analysis indicate that the Ag cannot be more than 0.5 A below the topmost layer of atoms in the structure, and that the most likely models for the geometry among the many proposed are the honeycomb-chained-trimer and the two-domain missing-top-layer Ag honeycomb. We also suggest that these two models may coexist and interconvert between one another with subtle changes in the local Ag coverage between 2 3 and 1 ML.