The formation of microvoids in MgO by helium ion implantation and thermal annealing

The formation of microvoids in metal oxides by helium implantation and ther mal annealing is observed under similar conditions as has been shown earlie r for silicon, Cleaved MgO (100) single crystals were implanted with 30 keV He-3 ions with doses varying from 10(15) to 10(16) cm(-2) and subsequently thermally annealed from RT to 1500 K, Monitoring of the defect depth profi le and the retained amount of helium was performed by positron beam analysi s and neutron depth profiling, respectively. For a dose larger than 2 x 10( 15) cm(-2) annealing of the defects was observed in two stages. at 1000 K h elium filled monovacancies dissociated, and other defects still retaining t he helium were formed, and at 1300 K all helium left the sample while an in crease of positron-valence-electron annihilations was observed, indicating an increase of the volume available in the defects. The voids of nm size we re located at shallower depth than the implanted helium. At lower dose no v oids were left after high temperature annealing. Voids can also be created, and even more effectively, by hydrogen or deuterium implantation. The void s are stable to temperatures of 1500 K;. The use of the nanovoids as a prec ursor state for nanoprecipitates of metals or other species is discussed. ( C) 1999 Elsevier Science B.V. All rights reserved.