THE INTERFACE STRUCTURE OF THIN LIQUID HEXANE FILMS

A series of thin liquid hexane films adsorbed on a rough silicon wafer was studied with specular and off-specular X-ray scattering. Assuming an interfacial profile at the liquid-solid interface which does not d epend on film thickness and modeling the density tail at the liquid-va por interface by an error-function, we find an interfacial profile whi ch explains the reflectivity data of all the measured 13 hexane films of thicknesses 25-350 Angstrom. The interfacial region near the substr ate extends to 40 Angstrom from the solid-liquid interface and is in g ood agreement with calculated density profiles of Lennard-Jones fluids near a hard wall. For films thicker than 50 Angstrom the rms-roughnes s found for the liquid surface accounts well to predictions based on s tandard continuum capillary-wave theory. The surface roughness of thin ner films is drastically reduced. Above 200 Angstrom a power law of th e form q(r)(eta-2) describes the diffusely scattered intensity. (C) 19 98 Elsevier Science B.V. All rights reserved.