CHARACTERIZATION OF LIF AND CAF2 SURFACES USING MIES AND UPS (HEI)

Metastable impact electron spectroscopy (MIES) and UPS (HeI) in combin ation with ab initio calculations (CRYSTAL-code) were applied to study surface and bulk defects in LIF and CaF2. The investigated stoichiome tric, defective and doped surfaces are LiF, LiF doped with Mg, and CaF 2. The experimental information obtained on the electronic structure o f stoichiometric and defective surfaces of LiF (100), LiF on W (110) a nd CaF2 (111) is discussed on the basis of the ab initio calculations. MIES spectra show features from Li agglomerates on the surface of ele ctron bombarded LiF. The electronic structure of the LiF:Mg single cry stal shows additional features above the valence band maximum caused b y the Mg doping, These are identified as caused by the formation of (M g-O) surface bonds. Exposure of CaF2 surfaces to X-rays (1486 eV) show s also formation of metallic regions on the surface. (C) 1998 Elsevier Science B.V.