Rapid synthesis and characterization of hybrid ZnOu core-shell nanorods for high performance, low temperature NO2 gas sensor applications

A rapid synthesis route for hybrid ZnOu core-shell nanorods has been realized for ultrasensitive, trace-level NO2 gas sensor applications. ZnO nanorods and hybrid ZnOu 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 ZnOu 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 ZnOu core-shell nanorods based sensor significantly decreased to 150 degree C compared to alternate NO2 sensors (300 degree 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 ZnOu core-shell nanorods influences local electron density, which in-turn indirectly influence the gas sensing properties. The ZnOu core-shell nanorods based sensor exhibited good selectivity toward NO2 and was found to be very stable.