Characterization of LiF and CaF 2 surfaces using MIES and UPS (HeI)

Metastable impact electron spectroscopy (MIES) and UPS (HeI) in combination with ab initio calculations (CRYSTAL-code) were applied to study surface and bulk defects in LiF and CaF 2. The investigated stoichiometric, defective and doped surfaces are LiF, LiF doped with Mg, and CaF 2. The experimental information obtained on the electronic structure of stoichiometric and defective surfaces of LiF (100), LiF on W (110) and CaF 2 (111) is discussed on the basis of the ab initio calculations. MIES spectra show features from Li agglomerates on the surface of electron bombarded LiF. The electronic structure of the LiF:Mg single crystal shows additional features above the valence band maximum caused by the Mg doping. These are identified as caused by the formation of (Mg O) surface bonds. Exposure of CaF 2 surfaces to X-rays (1486 eV) shows also formation of metallic regions on the surface.