Core-Electron Excitation Spectra of Si, SiO, and SiO2

The excitation spectra of $\mathrm{Si}\mathrm{}\left(2p\right)\mathrm{}$ and $\mathrm{O}\mathrm{}\left(1s\right)\mathrm{}$ core electrons, measured by low-energy electron-loss spectroscopy, yield detailed information on the excited states of Si, SiO, and Si${\mathrm{O}}_2$. The presence of an empty surface state near the top of the valence band on clean Si is directly demonstrated for the first time. For Si${\mathrm{O}}_2$, the results indicate the presence of five empty states in the conduction band.