Void formation in silica glass induced by thermal oxidation after Zn+ ion implantation

Thermal annealing effects on Zn+ ion-implanted silica glass (a-SiO2) have been studied in order to control void formation. Void formation in a-SiO2 with Zn+ ion implantation and subsequent oxidation has been observed using transmission electron microscopy (TEM). Zn+ ions of 60 keV were implanted into a-SiO2 to a fluence of 1.0 × 1017 ions/cm2. After the implantation, thermal annealing at 600 or 700 °C for 1 h in oxygen gas was conducted. In as-implanted state, metal Zn nanoparticles (NPs) of 10–15 nm in diameter are formed in the depth region around the projected range. The size of the Zn nanoparticles increases after the annealing at 600 °C in oxygen gas. Annealing in oxygen gas at 700 °C for 1 h caused two processes: (1) the migration of Zn atoms which formed Zn NPs in as-implanted state to the surface of the a-SiO2 substrate and (2) the transformation to the oxide phase on the substrate. The transportation of Zn NPs to the surface leaves voids of 10–25 nm in diameter inside the a-SiO2. These results indicate that the oxidation at 700 °C for 1 h causes the migration of Zn atoms to the surface without diffusion and recombination of vacancies which form the voids.