Fabrication and optimization of ZnO NR sensors in-situ grown on ITO substrates by a solution method

Abstract

ZnO nanorod (NR) arrays in-situ grown on indium tin oxide (ITO) substrates by a solution method are investigated by optimizing the solution concentration and the thickness of ZnO seed layer. Using 5–1000 ppm ethanol as the target gas, the gas sensor prepared with as-grown ZnO NR arrays in 25 mM solution with ∼ 10-nm thick ZnO seed layer is found to have the best gas response at 250 °C and exhibit a pretty good stability. The morphology of ZnO NR arrays is found important for optimizing the gas sensing property and is predominated by coalescence, which varies with solution concentration and the thickness of ZnO seed layer, thus leading to a variation in the defect density and surface state of ZnO NRs and enabling the gas sensing property not to be determined only by the specific surface area of ZnO NRs. Different thick ZnO seed layers will convert into the low-resistance states within a few seconds to minutes after applying an electric voltage and thus the role of ZnO seed layers in determining the gas sensing performance is mainly to control the diameter distribution of ZnO NRs, in which the arrays with a relatively large difference in the diameter of ZnO NRs would exhibit good gas response.