Evaluation methods for XPS depth profiling; A review

In recent years X-ray photoelectron spectroscopy (XPS) has become a widespread approach in modern material science to study numerous aspects (energy production, bio-interface analysis, catalysis etc.) of widely varied functional materials (metals, polymers, semiconductors). In the majority of these applications there is a need of the detailed knowledge of the surface and surface close chemistry. XPS with its excellent chemical sensitivity can directly be applied to the analysis of the surface layer in the range of some nms. In case of thicker regions, however, it has to be combined with various depth profiling techniques. The evaluation of depth profiles especially in case of ion etch techniques must be performed with special care due to the emergence of ion induced artefacts (mixing, preferential sputtering, roughening etc.). In this review we present the advantages and disadvantages of the techniques available for tackling these issues focusing especially on ion etching techniques: monoatomic and cluster argon sputtering. Evaluation problems are discussed through case studies aiming to provide a guide for choosing between the different methods, highlighting pitfalls and proposing solutions.