Enhanced ethanol sensing properties of ultrathin ZnO nanosheets decorated with CuO nanoparticles

Ultrathin two-dimensional ZnO nanosheets (NSs) with thicknesses of just a few nanometers have been fabricated by a solvothermal method. The very large surface area to volume ratio of this material translates into outstanding electrical sensing responses to ethanol (as high as S   ∼   97 to 200   ppm of ethanol at a working temperature of 320   °C). Decorating these ZnO NSs with CuO nanoparticles (NPs), by pulsed laser ablation of a CuO target at room temperature and then post-annealing at 400   °C, yields CuO-ZnO NSs that display a further up to 2-fold enhanced response to ethanol vapour, reduced sensor response and recovery times, high sensing repeatability and high selectivity. Mechanisms underpinning the enhanced sensing properties of the CuO-ZnO NSs are discussed in terms of CuO NP-induced p - n junction depletion regions and increases in the density of active sites for ethanol adsorption and for reaction with adsorbed oxygen species.