Radiation damage of epitaxial CaF₂ overlayers on Si(111) studied by photon‐stimulated desorption: Formation of surface F centers

The effects of radiation damage at the surfaces of CaF₂ films grown on Si(111) substrates have been studied and the electronic transitions responsible for the formation of surface F centers have been identified by photon‐stimulated desorption and soft x‐ray photoelectron spectroscopy. The dominant desorption channel for F⁺ ions is a direct Auger‐stimulated process following an electronic transition from Ca 3p to 3d‐derived states above the CaF₂ conduction band minimum. At the Si 2p edge, there is an indirect x‐ray induced electron‐stimulated desorption process that contributes only slightly to the desorption of F⁺. The changes in the kinetic energy distributions of the desorbing F⁺ ions as a function of film thickness are also discussed.