OFF-NULL ELLIPSOMETRY REVISITED - BASIC CONSIDERATIONS FOR MEASURING SURFACE CONCENTRATIONS AT SOLID LIQUID INTERFACES

The basic theory of off-null ellipsometry is described with emphasis on the determination of the surface concentration of adsorbed proteins on silicon substrates. The coupling between surface concentration and the off-null intensity is found by the use of de Feijters formula. Different optical models for adsorption processes are proposed. For surface concentrations below 5 ng/mm2, they all give a linear relation between the square root of the intensity and the surface concentration of the proteins. The accuracy is of the order of 3% or better. The range of validity of the linearity is discussed using linear expansions of the ellipsometric equations. © 1993 Academic Press, Inc.