E-beam induced damage in SiO2–Ge crystalline α-quartz, comparison with silica glass

Electron beam induced transformation in crystalline α-quartz doped with germanium was studied by mean of cathodoluminescence and of phase shift interferometric microscope. E-beams with low current (below 50 nA), defocused (diameter of spot about 40 μm) and with acceleration energy of 15 kV produce swelling of the irradiated volume about 100 nm above the non-irradiated surface. The luminescence of the self-trapped near germanium exciton (GeSTE) is observed mainly. No luminescence of the germanium related oxygen deficient center with bands at 290 and at 395 nm, usual for Ge-doped silica glass (GeODC), was observed. Defocused e-beam with higher current (about 200 nA), the same energy and similar dose, produces depression about 100 nm deep. In this case, we observed the band at 280 nm typical for SiODC in pure silica glass in the same time than the GeSTE already appearing for low current. However, we could not detect the band at 460 nm also typical for SiODC. It was, probably, obscured by the intensive band of GeSTE. We deduced that high density e-beam produces glass-like phase in the irradiated volume of α-quartz exhibiting the luminescence characteristic of pure silica glass. We explain, the absence of both bands related to GeODC in glass-like phase by a disappearance of germanium from this phase under irradiation.