Phase transitions in adsorbed layers formed on crystals of square and rectangular surface lattice

This article gives a survey of phase transitions in adsorbed films on well defined surfaces of square and rectangular symmetry of the lattice. The discussion concentrates on the effects of periodic changes of the adsorbate–substrate potential on the structure and thermodynamic properties of adsorbed films. Different theoretical approaches are briefly reviewed, with an emphasis on those which explicitly take into account final corrugation of the surface potential. Several aspects of statistical mechanical description of phase transitions in surface layers, such as order–disorder, melting, commensurate–incommensurate transitions in monolayer films as well as transitions connected with the formation of multilayer films (layering and wetting) are presented. Theoretical discussion is followed by the presentation of numerous experimental and computer simulation studies for various systems. Then the properties of monolayer films of molecular adsorbates on different substrates of a square and rectangular symmetry is discussed. It is pointed out that computer simulation methods provide a very powerful tool which allows to probe the inner structure of such systems and provides direct information concerning both orientational and positional ordering.