Molecular Layering on a Fluid Substrate

In a demixed binary-fluid system, a wetting layer of the most dense phase can intrude between the lighter phase and the vapour. Due to the first-order character of the wetting transition, a hysteresis can be observed leading to the formation of either a very thin or a thick film at the liquid/vapour interface. Ellipsometry experiments are presented which indicate that the thin film grows in layers with a thickness of the order of the molecular diameter, rather than continuously. The data show that a series of first-order layering transitions takes place at the interface.