An optical method of measuring the thickness of adsorbed monolayers

Abstract

The interferometric techniques developed by Tolansky have been used to study films adsorbed on solid surfaces. A monomolecular layer of fatty acid was spread by the retraction technique over part of a selected facet of a piece of mica. A highly reflecting layer of silver was then deposited on both sides of the mica specimen, and the thickness of the acid layer determined by multiple reflexion interferometry. The values so obtained were in agreement with X-ray data on the length of the fatty-acid molecule. Examination showed that the layers were uniform in thickness; polymolecular layers were absent. The method provides direct and independent evidence that molecules of a fatty acid, spread by the retraction technique, are adsorbed on a solid surface as a uniform monomolecular layer.