X-ray photoelectron spectroscopy using hard X-rays

Hard X-ray photoelectron spectroscopy (HAXPES or HXPS), using hard (2-15 keV) X-rays for excitation and high energy resolution, has shown a spectacular development recently, due to its capability for providing an insight into the bulk electronic structure of solids and the chemical composition of buried layers and interfaces lying at depths of several tens of nm. Following a summary of fundamentals concerning photoionization phenomena and transport processes of photoelectrons induced by hard X-rays from solids, examples of core level and valence band HAXPES spectra are presented to illustrate different physical effects. Examples are given of applications of HAXPES in determining electronic structure properties and in surface/interface chemical analysis of material systems of high practical interest. Finally, some perspectives for further developments are outlined.