Desorption of positive and negative fluorine ions from BaF₂ surfaces by core level excitation under electron bombardment

Electron stimulated desorption of negative and positive fluorine ions from BaF₂ surfaces has been studied as a function of impact electron energy. Thresholds observed for F⁺ and F⁻ are correlated with core‐level binding energies of Ba atoms. We propose that core level ionization of Ba ions, followed by an interatomic Auger decay involving halogen ions, can initiate F⁺ desorption, while the formation and subsequent breakup of superexcited molecular complexes containing a core hole can lead directly to the ejection of negative ions.