XPS

Photoelectron spectroscopy is based on the photoelectric effect: By excitation with photons, electrons are released from atoms, molecules or solids whose kinetic energy is determined.

Depending on the excitation source, a distinction is made between XPS (X-Ray Photoelectron Spectroscopy, excitation with X-rays, Eprim > 100 eV) and UPS (Ultraviolet Photoelectron Spectroscopy, excitation with UV radiation),
Eprim < 100 eV).