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

Abstract

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 (SiO2) were determined by SAXS as 7 nm and 13×1017 cm−3, 12 nm and 3.8×1017 cm−3, and 12 nm and 3.2×1017 cm−3 for fluences of 0.50, 1.0, and 2.0×1017 ions/cm2, 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 SiO2 is observed above the fluence of 1.0×1017 ions/cm2 due to sputtering loss. Thermal annealing in oxygen gas at 700 °C for 1 h induces the transformation of Zn NPs to both ZnO NPs and the Zn2SiO4 phase. With decreasing fluence, the branching ratio to the ZnO component decreases. This is because the reaction between tentatively formed ZnO NPs and the SiO2 substrate is enhanced by the higher surface-to-volume ratio of smaller NPs. At a fluence of 0.20×1017 ions/cm2, almost no ZnO component was detected. The size control of Zn and ZnO NPs is therefore possible only in a limited fluence region.