Characterization of LiF and CaF₂ 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 CaF₂. The investigated stoichiometric, defective and doped surfaces are LiF, LiF doped with Mg, and CaF₂. The experimental information obtained on the electronic structure of stoichiometric and defective surfaces of LiF (100), LiF on W (110) and CaF₂ (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 CaF₂ surfaces to X-rays (1486 eV) shows also formation of metallic regions on the surface.