Effects of annealing atmosphere on ZnO− ions-implanted silica glass: synthesis of Zn and ZnO nanoparticles

Abstract

The effects of annealing atmosphere (argon or oxygen) on Zn nanoparticles (NPs), embedded in silica glass, synthesized by implanting 50 keV ZnO− ions to a fluence of 7 × 1016 cm−2 have been studied. Optical absorption (OA) measurements carried out on the as-implanted samples have been found to result in a surface plasmon resonance (SPR) band centred at ∼255 nm due to the presence of Zn NPs in the silica glass. An increase in SPR peak intensity with a corresponding reduction of its full width at half maximum have been seen in the OA spectrum taken from the as-implanted sample following annealing in Ar ambient at 700 °C for 2 h, indicating a growth in the size of Zn NPs. However, annealing the as-implanted sample in O2 gas at 700 °C for 2 h has been found to result in a steep absorption edge at ∼364 nm in the OA spectrum which indicates the formation of ZnO NPs. These ZnO NPs show quantum confinement effects due to their small sizes. No observable photoluminescence (PL) emission has been seen from Zn NPs, whereas an excitonic band at ∼368 nm and three deep-level PL emission bands at ∼453 nm, ∼521 nm and ∼650 nm, respectively, have been seen from ZnO NPs. It was argued that the deep-level PLs were due to the singly ionized oxygen vacancies located at ZnO NPs' surfaces. These observations suggest that ZnO NPs were formed due to oxidation of Zn NPs via interaction with the indiffusing O2 molecules during annealing in O2 ambient, but not with the interaction of the implanted oxygen in silica glass.