Modulated Structures of Adsorbed Rare Gas Monolayers

Abstract

The structure of rare gas adlayers is determined by the interplay between the mutual interaction of the rare gas atoms and the interaction of the rare gas atom with the substrate. Depending on the relative magnitude of these interactions different types of structures of the first monolayer appear: if the mutual interaction is dominant the rare gas adlayer is incommensurate with the substrate. When the interactions are of the same order, a large variety of phases (incommensurate -I-, commensurate -C-, higher order commensurate -HOC) appear depending on temperature, coverage and the relative structure of the substrate and the of the bulk rare gas crystal. By varying the temperature and/or the coverage a whole series of phases are visited from commensurate, over striped and hexagonal incommensurate, to hexagonal incommensurate rotated, which ends in a high order commensurate phase. In between there are both first and second order phase transitions. On the other hand, when the lock-in forces of the substrate dominate, all or a fraction of the adatoms will always lock into preferential adsorption sites and commensurate or high order commensurate phases, repsectively, are energetically favored with respect to true floating incommensurate structures.