Energy loss in XPS: Fundamental processes and applications for quantification, non-destructive depth profiling and 3D imaging

Models for energy loss in XPS are reviewed. We start with rigorous models to describe the fundamental interaction of the electric fields from both the core-hole and the moving electron with the many-electron system of the solid and including also the influence of the surface and the interaction that takes place while the photoelectron moves in the vacuum. We then discuss the development of progressively simpler descriptions where different aspects of the rigorous model are treated approximately or ignored. These descriptions are less accurate but much more useful for practical data analysis. Applications for nano-scale quantification, non-destructive depth profiling and 3D imaging are discussed. The accuracy of the theory is in all parts validated by comparison to experiments.