Determination of thickness and composition of aluminium-oxide overlayers on aluminium substrates

A novel method is presented to determine the thickness and the composition of oxide films on metal substrates using the measured XPS spectra of the clean and the oxidised metal. The method is applied to aluminium-oxide films on aluminium substrates. The oxide-film thickness is derived from the primary zero-loss intensities of only the metallic and oxidic Al 2p main peaks, utilising the known value of the intrinsic bulk plasmon excitation probability for the Al 2p core-level photoelectron emission process. It is shown that this new method for layer-thickness determination gives results that can differ 20% from results obtained by the less correct methods used in common practice. The actual composition, expressed as the O/Al atomic ratio, of the oxide film is determined from the total primary zero-loss intensities of the O 1s peak and the Al 2p peak of Al 2p oxidic rest spectrum. This spectrum of the oxide is obtained after subtraction of a reconstructed metallic Al 2p peak from the measured XPS spectrum. (C) 1999 Elsevier Science B.V. All rights reserved.