A novel surface excitation in highly ionic fluorides

Abstract

Electron energy loss spectra of twelve alkali halides and three alkaline-earth difluorides were investigated systematically. A well-resolved surface excitation has been found in seven fluorides for low energy primary electron beams. The result of a shallow core excitation implies that the surface excitation corresponds to the transition of valence electrons to the lower lying surface state that derives from the metal atoms. On the other hand, the result of epitaxial fluoride films does not support the Rydberg-state model proposed for the surface excitation.