Metastable impact electron spectroscopy, and ab initio calculations were used to study surface and bulk defects. The stoichiometric, defective and doped surfaces investigated were LiF, Mg-doped LiF and CaF2. Experimental information on the electronic structure of the stoichiometric and defective surfaces of LiF (100), LiF /W(110) and CaF2 (111) was considered on the basis of ab initio calculations. The metastable impact electron spectra revealed features due to Li agglomerates on the surface of electron-bombarded LiF. The electronic structure of Mg-doped LiF single crystals exhibited additional features, above the valence band maximum, which were caused by the Mg doping. They were attributed to the formation of (Mg---O) surface bonds. The exposure of CaF2 surfaces to X-rays (1486eV) led to the formation of metallic regions on the surface.

Characterization of LiF and CaF2 Surfaces using MIES and UPS (HeI). D.Ochs, M.Brause, S.Krischok, P.Stracke, W.Maus-Friedrichs, V.Puchin, A.Popov, V.Kempter: Journal of Electron Spectroscopy and Related Phenomena, 1998, 88-91, 725-32