Variable-energy positron annihilation was used to study simple defects which were created in (100) samples by 1.0 or 2.6MeV proton irradiation at liquid N temperatures. The damage profiles, which were uniform over depths of several micrometers, were successfully scaled in accordance with the differing defect production rates of the 2 implantation energies. The S-parameter values were found to increase over some 3 orders of magnitude of irradiation fluence, before saturating at a value of 1.033 with respect to the bulk. The determination of the exact value was complicated by the presence of impurity-based defect complexes (especially B and O), but the latter value was thought to be representative of positron annihilation at di-vacancies within the lattice.

R.D.Goldberg, P.J.Schultz, P.J.Simpson: Applied Surface Science, 1995, 85, 287-91