Core-hole effects on electron energy-loss spectroscopy of ${\mathrm{Li}}_2\mathrm{O}$

Excitons in electron-energy-loss spectra (EELS) can be overwhelming in some materials. Here we report EELS from ${\mathrm{Li}}_2\mathrm{O}$ for both Li and O $K$ edges. Comparison with calculations excluding and including core-hole effects suggests that the one-electron (ground state) band structure theory is not valid for the interpretation of the fine structure in EELS of ${\mathrm{Li}}_2\mathrm{O}.$ Using a large angle scattering technique, a core exciton in the band gap can be observed in the $K$ edge EELS.