Samples of synthetic fused silica were implanted with 1.5MeV Si ions, at room temperature, to fluences which ranged from 1011 to 1013/cm2. The samples were investigated by means of variable-energy positron annihilation spectroscopy. The Doppler-broadening S-parameter which corresponded to the implanted region decreased with increasing fluence, and saturated at a fluence of 1013/cm2. It was shown that the decrease in the S-parameter was due to the suppression of positronium, which was formed in the pre-implanted material, due to competition with the implantation-induced trapping of positrons. However, it was necessary to account for the positron trapping that was due to defects which were created by both electronic and nuclear stopping of the implanted ions. It was found that annealing of the 1013/cm2 sample resulted in a measurable recovery of the pre-implanted S-parameter spectrum at 350C, and to complete recovery to the pre-implanted condition at 600C. Volume compaction was also observed after implantation. During annealing, the compaction decreased by 75%.

A.P.Knights, P.J.Simpson, L.B.Allard, J.L.Brebner, J.Albert: Journal of Applied Physics, 1996, 79[12], 9022-8