Multilayer adsorption and wetting: Ethylene on graphite

An ellipsometric technique was used to measure a set of adsorption isotherms for ethylene on a single cleaved surface of graphite in the vicinity of the triple point ($T_3$=104 K) of ethylene. At least seven or eight discrete layers are observed at temperatures slightly above $T_3$, contrary to a previous suggestion of a prewetting transition after two monolayers. Evidence is presented that this layered liquid film becomes unstable with repsect to bulk liquid at about ten layers, so that wetting is incomplete even above $T_3$.