Superstructure Formation

Abstract

This lecture presents a tutorial introduction to the ordering phenomena in monolayer films formed by atoms adsorbed on well denned crystalline solids. At first, some general relations between the symmetry of the surface lattice and the structure and symmetry of ordered states in adsorbed films are discussed. Then, the concept of order parameters is introduced and the question of universality classes of different order — disorder phase transitions is addressed. This rather general discussion is followed by the presentation of the experimental and theoretical results for the systems that can be described by lattice gas as well as by continuous space models. Here, we focus on the conditions under which the adsorbed layers form epitaxial structures. Additionally, the nature of melting transition of monolayer films is considered. Finally, the question of the commensurate — incommensurate transitions in adsorbed monolayers is addressed.