Fabrication and evolution of nanostructure in Al2O3 single crystals by Zn+ ion implantation and thermal annealing

(0001) α-Al2O3 single crystals (sapphire) were implanted with Zn+ ions at 60 keV to fluences of 1 × 1017 and 2 × 1017 ions/cm2; and were then annealed at different temperatures under oxygen ambient. Transmission electron microscopy and optical absorption spectra were used to investigate the formation of nanostructure and their thermal evolution. Our results clearly show that the evolution of ZnO nanoparticles depends strongly on the annealing temperature and time. Zn nanoparticles could be transformed into ZnO while for annealing at a temperature 600 °C. ZnO nanoparticles were formed in the Al2O3 when the sample was annealed at 700 °C for 1 h. However, while annealing at 700 °C for 2 h, ZnO single-crystal film was formed on the surface of Al2O3. Further increasing annealing temperature to 750 °C, polycrystalline ZnO nanoclusters were formed on the surface of the sample instead of ZnO film, and leaving nanovoids band in the implanted region for the sample implanted with higher fluence. All the Zn nanoparticles disappeared and transformed to ZnAl2O4 as the annealing temperature increased to 900 °C. Photoluminescence experiment was performed at room temperature to investigate the optical properties and the quality of formed ZnO on the surface of substrate.