Electron-energy-loss near-edge structure of Be2C

We describe both measurements and theoretical models of the beryllium carbide electron-energy-loss K-shell near-edge fine structure (ELNES). Methods for the interpretation of spectra obtained using transmitted kilovolt electrons and the very small probe sizes available in modern electron microscopes are discussed. Explicit constraints on the use of the projected local density of states used to interpret x-ray absorption near-edge structure are summarized. An initial attempt to interpret the measured ELNES using a tight-binding approximation plus core-hole impurity calculation shows good agreement for the carbon site, but poorer agreement for the Be site. Good agreement is obtained for both sites using a ground-state, real-space multiple scattering calculation if a charge corresponding to three electrons is assumed to be transferred from Be to C. This suggests that ground-state, one-electron theory and the muffin-tin form of the crystal potential may be a useful guide to the interpretation of near-edge structure in some ionic crystals if the effects of ionicity are explicitly incorporated.