Structural modification in amorphous silica after exposure to low fluence 355nm laser irradiation

UV laser irradiation induced structural modification in amorphous silica was characterized using Fourier transform infrared and X-ray induced photoelectron spectroscopy. Laser irradiation experiment was conducted using a 3Ie[control], 355nm beam from a pulsed Nd-YAG laser with pulse length of 6.8ns and laser repetition rate of 1Hz at ambient conditions. The examined laser fluence was controlled at a relatively low level, ranging from 0 to 4J/cm2. The IR spectra revealed that the vibration frequency of the rocking mode of SiOSi covalent bond shifted to lower wave number, while the bending mode and asymmetric stretching mode of SiOSi covalent bond shifted to higher frequency. This result suggested that the length of SiOSi covalent bond was decreased, the bond angle was increased and the irradiation modified material was densified after irradiation. The high resolution XPS spectra of Si 2p and O 1s illustrated the chemical shift of silicon and oxygen ions after irradiation. The XPS chemical shift of the Si 2p peak about 1.1eV revealed the existence of low valence silicon ions Si3+ species in silica glass after irradiation. The chemical shift of the O 1s peak about 0.9eV illustrated the emergence of non-bridging oxygen ions during laser irradiation. The deconvoluted peak area and FWHM value of low valence silicon ions and non-bridging oxygen ions all exhibited exponentially growth as the linearly elevation of laser fluence. UV laser-induced photolysis of SiO covalent bond was suggested to be responsible for the formation and increase of low valence silicon ions and non-bridging oxygen ions. These FT-IR and XPS data revealed that short range structural modifications were important structure alterations in silica glass before the emergence of distinct and large size damage crater.