Direct evidence by positron annihilation spectroscopy of defect distributions deeper than Rp in Ar+ implanted silica glass

Positron annihilation spectroscopy was used to depth profile the modification of intrinsic structural nanovoids in silica glass implanted with Ar+ ions at different fluences and implantation energies. Beyond an expected defect distribution below the ion projected range R-p, a second defect distribution extending more than two times deeper than R-p was revealed. This second defective layer was found to be related to recoiled oxygen atoms whose diffusion is probably increased by the stress gradient induced by the compaction of the first layer.