Formation processes of zinc-oxide nanoparticles by ion implantation combined with thermal oxidation

Abstract: Silica glasses (SiO2) were implanted with Zn+ ions of 60keV to a fluence of 1.0×1017 ions/cm2, and were annealed in oxygen gas flow at 700°C for 1h, to form ZnO nanoparticles (NPs). In as-implanted state, metallic Zn NPs of 10–15nm in diameter are formed between 10 and 50nm in depth. NPs are not observed on the surface and down to 10nm in depth. After the annealing at 700°C for 1h in oxygen gas, ZnO NPs of ∼10nm in diameter are observed around 50nm in depth. Moreover, droplet-like ZnO NPs larger than 30nm in diameter grow on the surface of SiO2 substrate. Migration of Zn atoms toward the surface, i.e., shallowing of the depth profile, is observed under the oxygen annealing, while vacuum annealing at the same temperature 700°C does not induce any prominent migration of Zn atoms. Mechanisms of the shallowing and the formation of ZnO NPs are discussed. [Copyright &y& Elsevier]