Fundamentals of high-energy electron-irradiation-induced modifications of silicate glasses

We report in situ observations of modifications in silicate glasses using electron-energy-loss spectrometry with a small-probe (2.2 Angstrom) scanning transmission electron microscope. Two silicate glasses CaO-Al2O3-SiO2 and ZnO-B2O3-SiO2 are examined. It is found that the nonbridging oxygen (NBO) in glasses plays a critical role in irradiation phenomena. We suggest that a highly localized density of states on the NBO's probably results in a very high sensitivity to electron irradiation of the cations bound to NBO's. These irradiation phenomena noted above reflect a tendency of electron irradiation to eliminate NBO's in the irradiated region.