Wetting and surface melting: Capillary fluctuations vs. layerwise short-range order

A dense liquid film on a solid surface has a smectic-like structure that gives rise to an attenuating periodic potential in which the free surface of the film fluctuates. At low temperatures this potential provides layering transitions and incomplete wetting. As the temperature rises capillary waves smear the oscillations of the potential which results in a critical wetting transition and layering critical point. The wetting transition provides a new example of strong fluctuational critical behaviour. In real systems with long-range interactions the prewetting phenomena may be observed. The theory estimates layering critical temperatures for He/H2. An extension of the analysis to a crystal surface covered with its own melt provides surface melting criteria for different faces of a given crystal in good agreement with recent observations. An exact criterion for the roughening of a melted surface is also obtained.