Formation of ZnO Nanoparticles by ZnO^- and O^- Dual Beam Ion Implantation and Thermal Annealing

ZnO nanoparticles have been synthesized by dual beam ion implantation into Si. 45 keV ZnO^- molecular ions and 15 keV O^- ions were implanted into Si at room temperature to fluences of 1 ×10¹⁷ and 2 ×10¹⁷ ions/cm², respectively. In the as-implanted sample, Zn nanoparticles with average crystalline size of ∼4.5 nm were observed to have formed and were distributed from the sample surface to a depth of ∼76 nm. The implanted sample was thermally annealed at a temperature of 700 °C in a mixture of Ar and H₂ for 1 h, after which both the Zn and O spatial distributions were observed to have broadened and ZnO nanoparticles with average crystalline size of ∼17.5 nm were formed. Due to the O^- ion implantation, a thickness of ∼38 nm of Si wafer was transformed into SiO₂, and the SiO₂ layer thickened to ∼57 nm when the sample was annealed. Binding energies of Zn increased in the annealed sample as compared to the as-implanted sample for all measured depths, consistent with the formation of ZnO bonding and indicating that ZnO had formed throughout the SiO₂ layer and slightly beyond.