AN ELLIPSOMETRIC STUDY OF ADSORPTION-ISOTHERMS

Adsorption isotherms of alkanes or silicone oil oligomers on silicon w afers covered with natural oxide, or bearing hydrophobic grafted layer s, have been studied at room temperature. At large thicknesses, inform ation on the long-range interactions is extracted, and plausible value s of the Hamaker constants, i.e. of the strength of the van der Waals interaction, are obtained for alkanes. At molecular thicknesses, the a mount adsorbed depends on the specific short-range interactions with t he surface layer. The presence of an adsorbed layer of water on the ba re silica surfaces must be taken into account in the interpretation of data.