Cleaved (100) single crystals were implanted with 30keV 3He ions to doses ranging from 1015 to 1016/cm2, and were then annealed at temperatures between ambient and 1500K. Monitoring of defect depth-profiles and retained He was carried out by using positron-beam analysis and neutron depth-profiling, respectively. Following doses larger than 2 x 1015/cm2, annealing-out of the defects was observed to occur in 2 stages. At 1000K, He-filled monovacancies dissociated and other defects which still retained He were formed. At 1300K, all of the He left the sample while an increase in positron and valence-electron annihilations was observed. This indicated an increase in the volume which was available in the defects. Voids of nm-size were located at shallower depths than the implanted He. At lower doses, no voids were left after high-temperature annealing. Voids could also be created, even more effectively, by H or D implantation. The voids were stable at temperatures of up to 1500K.

The Formation of Microvoids in MgO by Helium Ion Implantation and Thermal Annealing. A.Van Veen, H.Schut, A.V.Fedorov, F.Labohm, E.A.C.Neeft, R.J.M.Konings: Nuclear Instruments and Methods in Physics Research B, 1999, 148[1-4], 768-72