Fabrication And Gas Sensing Property Of ZnO-based Nanorods Array

As one of the earliest practical gas sensing materials, ZnO semiconductor has become widely used in various forms of gas sensors, including sensors made from powder and films, although their sensitivities are not high enough for detecting very low concentration of reductant/oxidant gases. Recently, many studies show that utilization of nanomaterials, such as ZnO nanowires or nanorods can elevate the gas sensing performances due to their large surface-to-volume ratio, and extensive studies have also been done in improving the performances by adding catalysts, doping metals and metal oxides to ZnO nanowires or nanorods.In this thesis, wurtzite ZnO nanorods array with high c-axis preferential orientation have been prepared using a two-step solution method. The results showed that, the ZnO nanorods prepared were uniform with diameters of 40-80 nm and lengths about 1.1μm. ZnO nanorods array with Al³⁺ dopant or Au nanoparticle modification were also fabricated, the morphology and structure of the as-prepared samples were characterized.The gas sensing results show that the ZnO:Al³⁺ nanorods array exhibit good sensing properties for LPG and ethanol at working temperature about 340-380℃. Among all doped nanorods array samples studied, the 0.5 wt% Al-doped ZnO nanorods array sensing unit reaches the maximum sensitivity of 11.5 and 32.8 to 1000 ppm LPG and ethanol, respectively. The response times for 1000 ppm LPG and ethanol are found to be less than 30 s and 20 s, respectively.The gas sensing properties of the Au-modified ZnO nanorods array to ethanol, LPG and formaldehyde were also investigated. Sensitivity of 63.5 to 100 ppm ethanol, 36.2 to 500 ppm LPG, and 35.6 to 500 ppm formaldehyde, are obtained utilizing the ZnO nanorods array modified by 11 nm Au nanopartiles as sensing unit at working temperature of 300-340℃.The wettability measurement of ZnO and ZnO:Al³⁺ nanorods array show that they are all hydrophobic, but ZnO:Au nanorods array is hydrophilic due to the formation of Au nanopartiles on the surface. The Photoluminescence (PL) spectrum of ZnO nanorods array mainly consisted of two emission bands: the UV near-band-edge emission (NBE) at about 391 nm, and the visible emission.