Effects on structure, surface oxygen defects and humidity performance of Au modified ZnO via hydrothermal method

In this paper, different approaches for the preparation of gold (Au) modified zinc oxide (ZnO) humidity sensors were investigated. Experimental results show that ZnO modified with gold nanoparticles (AuNPs) or chloroauric acid (HAuCl4) enhances the concentration of oxygen vacancy defects on the surface of ZnO, which can improve the sensitivity of such a ZnO humidity sensor. As compared to AuNPs-modified ZnO, the modification of HAuCl4 reduces the size of ZnO and Au particles and exhibits better humidity performance. This is due to that smaller Au particles can further promote dissociation and electrolysis conduction processes so as to enhance the adsorption activity of HAuCl4-modified ZnO nanocomposites. Humidity experiments indicate that HAuCl4-modified ZnO acquires more than 4 orders of magnitude for the impedance changes in RH range from 11% to 95% with high sensitivity, good linearity, small hysteresis (~2.35%) and short response/recovery time (15 s/6 s). The results indicate that smaller Au particle can improve the hysteresis and response of the ZnO humidity sensor. Thus, Au particles with small size are a key parameter for the design of Au modified ZnO humidity sensors with high performance, which has a potential in the fast detection of humidity.