Abstract
Technological applications of nano-structured materials are steadily increasing and to create materials with optimized properties, it is of utmost importance to have non-destructive techniques to characterize elemental depth distributions at the nm scale. X-ray photoelectron spectroscopy (XPS) is ideal for this because it is sensitive on the nm depth scale and it is today widely used by industry. In the large majority of labs it is used within a formalism that relies on the measured peak intensities. In this paper we first point out the large uncertainties and the misleading results that result from such a formalism. We then review techniques that rely on analysis of a wider range of the energy spectrum around the XPS peak rather than just at the peak energy. This results in a much improved accuracy. It is first shown how a simple visual inspection of a survey XPS spectrum can be used to immediately get a rough picture of the nano-structure of the sample. For more accurate quantitative analysis, algorithms have been developed which are implemented in the QUASES (Quantitative Analysis of Surfaces by Electron Spectroscopy) software. The application of this software in practical analysis is discussed. Then it is discussed how this can be combined with synchrotron radiation at high photon energies (HAXPES) to provide analysis of structures buried more than 50 nm in a stack. Finally we discuss a newer algorithm which is less accurate but which has the advantage that it is suitable for automated XPS analysis for determination of the structure. This can be useful for routine analysis and has also been applied to 3-dimensional imaging of surface nano-structures.
