Surface Vibrations of Silicon Detected by Low-Energy Electron Spectroscopy

The energy loss of 5-eV electrons reflected from clean and from oxidized (111) silicon surfaces has been investigated. A surface phonon with $\hslash \omega \approx 55$ meV, $k\approx 0$ is found at the clean surface. After exposure to ≅${10}^{-5\mathrm{}}$ Torr min oxygen, three energy losses at 48, 90, and 125 meV occur. Models for the electron-phonon interaction, the nature of the surface phonon, and the structure of the oxidized surface are proposed.