Recrystallization-driven migration of implanted ions in sapphire and resultant-oriented precipitation

The migration of Cr, Mn, Ni, and Xe implanted in sapphire during post-implantation thermal annealing is investigated by Rutherford backscattering (RBS)/channeling studies. Thermal annealing was performed in air or in vacuum. It is shown that the epitaxial recrystallization of the implantation-damaged region dominantly causes the migration of the implanted ions when there is little or no solid solubility of the ion species in sapphire. This migration mechanism strongly relates to the formation of oriented precipitates. When the implanted ions migrate toward the surface, surface precipitates of oxides are formed with annealing in air. On the other hand, when the implanted ions concentrate around the projected range at an elevated temperature, metals mainly precipitate in the substrate. The following crystallographic relations are found between the precipitates and the substrates: (111) MnAl2O4, (111) NiAl2O4, (111) Ni or (110) Cr∥(0001) Al2O3, and (103) Mn3O4∥(112̄0) Al2O3.