RHEED INTENSITY ANALYSIS OF SI(111) SQUARE-ROOT-3 X SQUARE-ROOT-3-AG STRUCTURE

Rocking curves of reflection high energy electron diffraction (RHEED) intensities from the Si(111)√3×√3-Ag surface were analyzed by RHEED dynamical calculations for several models consistent with the results of scanning-tunneling-microscope observations. From dynamical analyses it is shown that honeycomb models with 2 3 monolayer coverage of silver atoms give no agreement with the present rocking curves. The best model is a missing-top-layer one with trimer Ag and Si layers. The Ag and the Si layers are 2.95±0.05 Å and 2.2±0.1 Å above the bulk-like Si layer, respectively. The Ag trimers are chained in a honeycomb arrangement. The Si trimer is at the center of the honeycomb chain and twisted about ±20° in the surface. The Ag-Ag distances are 5.38 and 3.36 Å, and the Si-Si distance is 2.7±0.5 Å. © 1989.