THE USE OF OVERLAYER EQUATIONS IN AN X-RAY PHOTOELECTRON-SPECTROSCOPY STUDY OF THE ADSORPTION OF LONG-CHAIN ALCOHOL MOLECULES ON SILICA SURFACES

A series of long-chain alcohols of differing chain lengths were adsorbed on silica plates. X-ray photoelectron spectroscopic measurements of the Cls, Si2p and Ols signals were used to determine the thickness of the adsorbed layer at a constant angle between the surface and the analyser with varying film thickness, or at variable angles with constant film thickness. Quantification of the layer thickness of the adsorbed long-chain alcohol molecules is made by calculation of attenuation lengths (ALs) for comparison with values predicted from empirical equations and those reported experimentally. It is predicted that the surface coverage of the silica plates is in the range of 2-3 alcohol molecules per square nanometre, corresponding to AL values for Cia electrons in the range of 3-4 nm. Problems associated with the calculation of AL values from overlayer equations are discussed.