Gas Sensing Property, Photoluminescence And Wettability Of ZnO Nanopillar Array

The sensitivity and selectivity of traditional semiconductor metal oxide sensors prepared using powders with grain size in micron or nano range were not high enough to detected very low concentration gases due to their grain growth when they were working at relatively high temperature, It should be possible to increase the sensing properties of these sensors with 1-D nanostructures array.ZnO nanorods array on different kinds of substrates were prepared by a two-step solution method. The corresponding gas sensitivity, photoluminescence and wettability were investigated, and the gas sensitivity of ZnO nanorods covered with TiO2 was studied as well. The main findings are as following:1. Preparation of ZnO nanorods array via a two-step solution approach. The ZnO sol was prepared through Zn(Ac)12 hydrolysis, then the ZnO sol prepared was coated onto glass or Al2O3 tubes , annealed at 200~600℃, ZnO film precursor with the diameter of 5~20nm was obtained.Large-area, well-aligned ZnO nanorods can be obtained by further reaction on the ZnO precursors, the diameters and lengths of the obtained ZnO nanorods array are in the range of 20~200nm and 50nm~2μm respectively. The as-prepared ZnO nanorods are wurtzite structure with preferentially c-axis orientation.2. Sensitivity measurement of ethanol and hydrogen showed that at the temperature of 350℃, the aligned ZnO nanorods gas sensor exhibited a sensitivity of 71.104 and 30.076 to 2500ppm ethanol and hydrogen respectively, the sensitivity achieved 10.573 even being exposed to the gas concentration as low as 50ppm ethanol. The sensitivity test of ethanol and hydrogen showed that the aligned zinc oxide nanorods devices had an improved sensing performance compared with the reported ZnO nanoparticle sensors.An investigation on the gas sensor of ZnO-TiO2 composite showed that at 350℃, the sensitivity of ZnO-TiO2 composite are 74.949 and 52.09 to 2500ppm ethanol and hydrogen respectively. Either pure ZnO nanorods or ZnO-TiO2 composite gas sensors showed relatively higher sensitivity to ethanol than to hydrogen.3. In contrast to the photoluminescence spectra gathered from ZnO film, the emission band of ZnO nanorods red-shifted to the position around 399.8nm, and the intensity of violet luminescence decreased greatly compared with that of ZnO film sample. Nevertheless, the intensity of blue luminescence was relatively increased.4. The wettability of ZnO nanorods array was evaluated via contact angular measurement. Results showed that the hydrophilicity of ZnO nanorods array decresed as the heat-treatment time increased at the temperature of 300℃.