X-Ray Photoelectron Spectroscopy of Solids; Evidence of Band Structure

X-ray photoelectron spectra of solid ${\mathrm{Cu}}_2$O, CuCl, CuO, CuS, and CuS${\mathrm{O}}_4$ were measured. In all cases, satellites having various degrees of complexity are seen adjacent to the (Cu) $2p$ photolines. A multiple-excitation mechanism is proposed for the explanation of these satellites. The satellites are formed when the emission of a $2p$ photoelectron takes place in parallel with a valence-band-conduction-band excitation. These photolines are thus emitted with kinetic energies lowered by the amounts of allowed interband transitions.