Chemical vapour deposited ZnO nanowires for detecting ethanol and NO2

Randomly oriented ZnO nanowires were grown directly onto alumina substrates having platinum interdigitated screen-printed electrodes via the chemical vapor deposition method using Au as catalyst. Three different Au film thicknesses (i.e., 3, 6 or 12 nm) were used in the growth of nanowires, and their gas sensing properties were studied for ethanol and NO2 as reducing and oxidizing species, respectively. ZnO nanowires grown employing the 6 nm thick layers were the less defective and showed the most stable, repeatable gas sensing properties. Despite ZnO nanowires grown employing the thickest Au layers reached the highest responses under dry conditions, ZnO nanowires grown using the thinnest Au film were more resilient at detecting NO2 in the presence of ambient moisture. The gas sensing results are discussed in light of the defects and the presence of Au impurities in the ZnO nanowires, as revealed by the characterization techniques used, such as X-ray diffraction, field-emission scanning electron microscopy, X-ray photoelectron spectroscopy and photoluminescence spectroscopy. Promising results were obtained by the implementation of ZnO NWs directly grown over alumina substrates for the detection of ethanol and NO2, substantially ameliorating our previously reported results