Rapid synthesis and characterization of hybrid ZnO@Au core–shell nanorods for high performance, low temperature NO2 gas sensor applications

Abstract

A rapid synthesis route for hybrid ZnO@Au core–shell nanorods has been realized for ultrasensitive, trace-level NO2 gas sensor applications. ZnO nanorods and hybrid ZnO@Au core–shell nanorods are structurally analyzed using X-ray diffraction (XRD), high resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Optical characterization using UV–visible (UV–vis), photoluminescence (PL) and Raman spectroscopies elucidate alteration in the percentage of defect and charge transport properties of ZnO@Au core–shell nanorods. The study reveals the accumulation of electrons at metal–semiconductor junctions leading to upward band bending for ZnO and thus favors direct electron transfer from ZnO to Au nanoclusters, which mitigates charge carrier recombination process. The operating temperature of ZnO@Au core–shell nanorods based sensor significantly decreased to 150°C compared to alternate NO2 sensors (300°C). Moreover, a linear sensor response in the range of 0.5–5ppm of NO2 concentration was observed with a lowest detection limit of 500ppb using conventional electrodes. The defects with deep level, observed in ZnO nanorods and hybrid ZnO@Au core–shell nanorods influences local electron density, which in-turn indirectly influence the gas sensing properties. The ZnO@Au core–shell nanorods based sensor exhibited good selectivity toward NO2 and was found to be very stable.