Incident fluence dependent morphologies, photoluminescence and optical oxygen sensing properties of ZnO nanorods grown by pulsed laser deposition

Abstract

ZnO nanorod (NR) samples have been prepared by 248 nm pulsed laser deposition using three different fluences, F, at the target surface. F is shown to influence the sample morphology and its photoluminescence (PL) properties. Use of large F (∼4.0 J cm⁻²) results in ZnO NRs with relatively low surface area to volume (S/V) ratio, the PL spectra of which are characterized by a weak near-UV component (I_UV) and a relatively intense visible (I_vis) emission feature attributable to the presence of zinc rich and oxygen deficient defects. Use of small F (∼1.2 J cm⁻²) yields ZnO NRs with larger S/V ratio, and a much increased I_UV/I_vis emission ratio. The O₂ sensing properties of these NR samples have been investigated by monitoring I_UV as a function of O₂ partial pressure, over a range of working temperatures (room temperature to 240 °C). All of the NR samples are shown to function as optical O₂ sensors, the responses of which are enhanced by operating at elevated temperatures, but the detailed sensitivity (and its temperature dependence) are shown to be strongly dependent on their (F-determined) S/V ratio and defect density.