Surface enrichment of Li on LiF single crystal after cleaving or under electron bombardment

Abstract

The build-up of an excess metal layer on the surface of LiF(100), after cleaving or due to electron irradiation, is examined by monitoring the neutral atom and molecule emission during sputter depth profiling. At room temperature the Li enrichment on the surface saturates at an electron fluence of 2.5 × 10 15 electrons cm 2 at 500 eV energy. In addition, lesser enrichment of the crystal surface by Li after cleavage without electron irradiation was observed, which also reappears after removal by moderate sputtering by a 3 keV ion beam. Enrichment is attributed to the difference in the formation energies of cation and anion vacancies. The time constants for the build up of the metal layer at room temperature for the unirradiated but cleaved crystal and the cleaved crystal exposed to the saturation dose of electrons are 2 and 40 min, respectively.