Thin CaF 2 films with thicknesses between 1 and 100 nm were grown on Si(1 1 1) at UHV conditions by evaporation from a CaF 2 source. The correlation of film composition and growth morphology with the deposition parameters was studied by various techniques such as heavy-ion elastic recoil detection analysis (ERDA), RBS/channeling, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and auger electron spectroscopy (AES). The composition and morphology of the CaF 2 films strongly depend on the substrate temperature during deposition. Epitaxial growth is observed at deposition temperatures higher than 450°C. The F/Ca ratio of the films in the monolayer range is found to deviate appreciably from the stoichiometric composition (F/Ca=2) suggesting that the interface composition does not obey the rules of bulk equilibrium chemistry. AES results show the formation of different bonding configurations (in particular of silicide-like bonds) at the CaF 2/Si interface.