Activation energy spectra for annealing of ion irradiation induced defects in silica glasses

In situ stress measurements were performed on alkali-borosilicate glass samples during and after 2 MeV Xe ion irradiation at several temperatures between 95 and 580 K. After switching off the ion beam, stress changes are observed that are related to the annealing of ion beam generated defects. The activation energy spectra for defect annealing are obtained from the data at each irradiation temperature. Defects are observed in the energy range from 0.26 to 1.85 eV. At each temperature the spectrum increases monotonously with activation energy. At each energy the defect density per unit energy is smaller at higher temperatures. This behavior can be explained using a binary collision model. The data are contrasted against the results obtained for 4 MeV Xe ion irradiation of thermally grown SiO. films, which can be explained using a thermal spike model. Measurements of the radiation induced viscosity support these ideas.