Synthesis and surface reactivity of ZnO: application to gas and photon detection

Abstract

This work employs different synthesis techniques to control the surface properties of polycrystalline ZnO for sensing device applications. ZnO micro-scale and nano-scale particles were made by various solid-state, solvothermal, and high temperature synthesis techniques that are designed for controlling crystal habit, surface polarity and surface area. The ZnO samples exhibited different degrees of degradation when exposed to ambient water and CO2, which were linked to ZnO surface dissolution and crystal growth conditions. In addition, a strategy for controlling the hydroxide in the products of the solid-state metathesis has been developed. Thin film gas sensors were assembled using the ZnO products. The capacitance responses of ZnO particles were evaluated after exposure to volatile organic compounds (ethanol and hexane) at various operation temperatures between 20 and 500⁰C. The results showed that gas sensing processes at low temperatures were mediated by the ambient humidity when detecting hydrophilic gases, and the responses from ZnO nanoparticles were greatly enhanced at high temperatures. Furthermore, a preliminary study for UV activated gas sensing was conducted to examine the effect of UV light radiation on the electrical properties of the ZnO samples, in which the AC frequency dependence of the photoresponse was revealed by electrical impedance spectroscopy.