Surface Modification of Sapphire by Magnesium-Ion Implantation

Single crystals of Al₂O₃ were implanted at a temperature of 25°C with magnesium ions that were accelerated at 200 keV and then annealed in oxygen gas for 15 h at 1500°C. The microstructure and composition in the implanted region were examined using analytical electron microscopy techniques, with an emphasis on identification of the microstructural changes that were caused by implantation and annealing. Implantation created a damage zone 0.3 µm thick in the near-surface region of sapphire, and implanted magnesium ions were distributed in this zone without detectable precipitation. Annealing in oxygen gas caused redistribution of the implanted magnesium ions and the formation of a discrete buried layer of spinel (MgAl₂O₄) that was epitactic with both the substrate and the cap layer.