Quantitative AES depth profiling of thin oxide films grown on stainless steels and aluminium

AES depth profiling was performed in passive overlayers grown on the surface of stainless steels and in alumina films formed on aluminium at 250°C in oxygen. Our quantitative approach is based on the sequential layer sputtering model proposed by Benninghoven and Hofmann for analysis of thin layers (<10 nm). A careful measurement of AES sensitivities in pure standards constituted by metallic elements (for the substrate) and their corresponding normal oxides (for the film) is needed to achieve the necessary conversion of AES sputter profiles into atomic concentration profiles. With the assumptions of (1) an oxide film and a metallic substrate assimilated to two distinct media separated by a step-like interface and (2) a time-invariant sputter rate, the method provides an available determination of the film thickness mainly dependent on an appropriate choice for attenuation lengths of Auger electrons. The usual approximations and results should therefore be discussed in the light of the determination of absolute oxygen film contents by means of nuclear reaction analysis (NRA).