Fluence-dependent formation of Zn and ZnO nanoparticles by ion implantation and thermal oxidation: An attempt to control nanoparticle size

摘要

For possible control of the size of nanoparticles (NPs), the fluence-dependent formation of Zn and ZnO NPs by ion implantation with and without thermal oxidation was investigated by optical absorption spectroscopy, Rutherford backscattering spectrometry, and small-angle x-ray scattering (SAXS). The mean diameter and number density of Zn NPs in the as-implanted state in silica (SiO_2) were determined by SAXS as 7 nm and 13 × 10~(17) cm~(-3), 12 nm and 3.8 × 10~(17) cm~(-3), and 12 nm and 3.2 × 10~(17) cm~(-3) for fluences of 0.50, 1.0, and 2.0 × 10~(17) ions/cm~2, respectively. With increasing fluence, the mean diameter of the NPs increases and the number density decreases. However, an upper limit of the NP size and Zn concentration in SiO_2 is observed above the fluence of 1.0 × 10~(17) ions/cm~2 due to sputtering loss. Thermal annealing in oxygen gas at 700 ℃ for 1 h induces the transformation of Zn NPs to both ZnO NPs and the Zn_2SiO_4 phase. With decreasing fluence, the branching ratio to the ZnO component decreases. This is because the reaction between tentatively formed ZnO NPs and the SiO_2 substrate is enhanced by the higher surface-to-volume ratio of smaller NPs. At a fluence of 0.20 × 10~(17) ions/cm~2, almost no ZnO component was detected. The size control of Zn and ZnO NPs is therefore possible only in a limited fluence region.