Structures and transitions of Cs monolayers on Rh(100): Leed study and model calculations

Abstract

At T ≈ 120 K cesium is observed to order in several commensurate and incommensurate superstructures, including also a “rotational epitaxy” phase. The diffraction patterns of the commensurate structures are interpreted by the assumption of high symmetry adsorption sites and a repulsive interaction between adatoms. The latter forces the adatoms to adsorb at maximum mutual distance but must compete with their tendency to occupy high symmetry sites. A phase diagram is determined and discussed. Monte Carlo and mean field calculations are applied to reproduce the main features of the phase diagram on the basis of a simple lattice gas model. In fact, assuming dipole-dipole repulsion up to third-nearest neighbours and an additional hard core interaction, all superstructures are reproduced assuming different types of non-equivalent adsorption sites.