Films of ZnO, grown onto sapphire substrates, were implanted with 100keV Li ions up to a total dose of 1016/cm2. Vacancy-type defects, mostly vacancy clusters, were observed by positron annihilation measurements after implantation. Upon annealing, they first had an agglomeration process which led to the growth in the vacancy size. After annealing at about 500C, vacancy clusters grew into micro-voids, which was indicated by the positronium formation. With annealing temperature increased to above 500C, the micro-voids begin to recover, and finally all the implantation-induced vacancy defects were removed at 1000C. No Li nanoclusters could be observed after Li+ implantation.

Energy Variable Slow Positron Beam Study of Li+-Implantation-Induced Defects in ZnO. Chen, Z.Q., Maekawa, M., Kawasuso, A.: Chinese Physics Letters, 2006, 23, 675-7