XPS and UPS are perfect tools to determine band alignments at heterointerfaces of materials. The same methods also allow for the detection of chemical changes due to chemical reactions at the interface of two materials or migration processes. Unfortunately often the films are too thick for XPS to still detect electrons from the interface. Increasing of the escape depth of the electrons by increasing the photon and thus the kinetic energies is helpful. So with HAXPES such studies are possible.