Reflection electron energy loss studies were made of monocrystalline (10•0) and (00•1) quartz samples. Bulk single loss structures appeared at 10.5, 12.5, 14.3, 17.9 and 21.3eV. The 10.5eV peak was attributed to the SiO2 exciton, the 21.3eV peak was attributed to the SiO2 plasmon, and the other 3 transitions were of inter-band type. The experimental results showed that 2 electronic transitions, at 5.1 and 7.2eV, appeared in the gap of -quartz under phonon excitation (ultra-high vacuum heating), atomic excitation (collision between 7keV ions and nuclei of surface and near-surface atoms), and electronic excitation (interaction with 350eV electron beam). The defects which were responsible for these structures were located at the surface and were related to the neutral O vacancy which was the precursor of the E' center.

F.Bart, M.Gautier, F.Jollet, J.P.Duraud: Surface Science, 1994, 306[3], 342-58