VALENCE-BAND ENERGY-MOMENTUM DENSITIES OF AMORPHOUS SIO2 BY (E,2E) SPECTROSCOPY

We have measured the energy-momentum density of amorphous silicon diox ide using an (e,2e) spectrometer with 20.8 keV incident, 19.6 keV scat tered, and 1.2-keV ejected electron energies. The amorphous SiO2 sampl e was prepared by oxidizing a thin silicon membrane. The experimental data show a valence electronic structure characteristic of upper p-lik e and lower s-like bands. The width of the upper valence band is 10 eV . This is separated by 9 eV from the lower valence band, which exhibit s 2-eV dispersion. We have calculated the energy-momentum density of a lpha-quartz using the ab initio linear muffin-tin orbital method and t he result is spherically averaged over all crystal directions to enabl e comparison with the experiment. The calculated electron momentum den sities show very good agreement with experiment for both the upper and lower valence bands. The theoretical prediction of the energy separat ion between the upper and lower valence bands is about 2 eV smaller th an that measured and this discrepancy is discussed. The agreement betw een theory and experiment suggests that the short-range order in silic on dioxide plays an important role in determining the electronic struc ture of this material. [S0163-1829(98)04908-X].