An increased F2-laser damage in ‘wet’ silica glass due to atomic hydrogen: A new hydrogen-related E′-center

A dramatic increase of F2-laser induced room temperature-stable point defects in ‘wet’ synthetic silica glass occurs when irradiation temperature is lowered to 80 K. Contrary to the predictions based on the established models of defect processes, a large part of defects induced at 80 K remains stable also at the room temperature. The intensities of the laser-induced optical absorption bands of the non-bridging oxygen hole centers (2.0 and 4.8 eV) and E′-centers (5.8 eV) are comparable to those created by neutron irradiation (1018 n/cm2). A growth of infrared absorption peak at 2237 cm−1 indicates creation of silicon hydride (SiH) groups. A study of irradiation dose dependences and irradiation efficiency at intermediate temperatures (160 K) suggests a novel radiation damage mechanism by insertion of atomic hydrogen in electronically excited Si–O bond. EPR spectra show E γ ′ -like centers overlapped by a new type of E′-centers, characterized by a hyperfine splitting of 0.08 mT of the low-field peak in the derivative spectrum. The new E′-center is assigned to a silicon dangling bond, with the Si atom bonded by two bridging oxygens and an OH group (‘E′(OH)’). Similar centers have been previously observed on SiO2 surfaces.