F+-DESORPTION MECHANISM FROM A CAF2(111) SURFACE BY LOW-ENERGY ELECTRON-IRRADIATION

Electron stimulated desorption (ESD) of F+ ions from the (111) surface of an epitaxially grown CaF2 film is observed in the incident electron energy region above 28 eV. The threshold energy of ion desorption corresponds to the binding energy of the Ca 3p energy level in the CaF2 crystal. ESD of F+ ions arises from the interatomic Auger decay of a Ca 3p core-hole. The energy produced by the core-hole decay turns out to be used for the formation energy of a new level near the Fermi level and the kinetic energy of the desorbed ion. The kinetic energy distribution of the desorbed ions can be expressed as a convolution of the Ca 3p and F 2p spectral functions deduced from photoemission data.