BULK AND SURFACE ELECTRONIC-STRUCTURE OF LI2O

We have used photoemission and electron-energy-loss spectroscopies to determine the surface and bulk electronic structure of a single-crysta l sample of the alkali-metal oxide Li2O. The predominately O 2p valenc e band exhibits two main features in the photoemission spectrum, whose relative widths are consistent with results of an ab initio Hartree-F ock calculation of the bulk electronic structure. However, changes in the intensity of the two features as a function of the exciting photon energy are large and not understood. Energy-loss spectra show the pre sence of a strong surface exciton in the bulk band gap of Li2O; such e xcitonic surface states do not exist for the alkali halides. Its energ y is about 2 eV less than the bulk band gap, similar to the surface ex citonic shifts that have been observed in the alkaline-earth oxides.