Vapor adsorption on mica and silicon : entropy effects, layering, and surface forces

Using an angle-averaging, refractive-index-matching ellipsometric technique, absorption isotherms of n-pentane, cyclohexane, tetrachloromethane, and OMCTS are measured. OMCTS on silicon has a different isotherm than the other nonpolar liquids, which are all very similar. Up to half a statistical monolayer thickness, all isotherms except OMCTS are smooth and linear. At separations below 2 nm, none of the isotherms agree with the Lifshitz of van der Waals forces. If the substrates are smooth and homogeneous, structural effects may be present in many liquid adsorbed films at room temperature. 69 refs., 11 figs.