Abstract
In this work, nitric oxide (NO) gas sensors based on the ZnO nanowires (NWs) modified with Cu2O nanoparticles (NPs) are reported. The ZnO NWs are grown on Ti electrodes substrates of 300 nm thick created by photolithography using a solution method and then modified with Cu2O NPs by photoreduction. To facilitate crystallization, the ZnO NWs and Cu2O NPs are also subjected to thermal annealing. The sensing principle is due to the fact that NO is an oxidizing gas and the adsorption of gas molecules on the NWs surface causes the NWs conductance to decrease. By monitoring changes in the sensor current, we can calculate the response of the gas sensor. The results of scanning electron microscopy show the morphologies and structures of nanowires and nanoparticles. The ZnO NWs modified with the best concentration of Cu2O NPs show the best NO gas sensing under the condition of two hours photoreduction with 10-4 M copper sulfate. The ultraviolet emissions of the modified ZnO NWs decrease and the green emissions of the modified ZnO NWs increase in the photoluminescence spectra, revealing that the recombination of electron-hole pairs is reduced and the number of O vacancies (Vo) is increased by Cu2O NPs. The results of 1 ppm NO gas sensing by using UV activation under ambient environment show the response of the unmodified ZnO NWs sensor is 25%, whereas the response of the Cu2O NPs modified ZnO NWs sensor is 357%, which is 14.28 times as high as that of the unmodified ZnO NWs sensor. A response of 8% has also been achieved at 60 ppb NO. On the other hand, the results of 1 ppm NO gas sensing by using UV recovery show the response of the Cu2O NPs modified ZnO NWs sensor is 28%. A response of 4% has also been achieved at 60 ppb NO. A high-efficiency NO gas sensor is successfully fabricated by a simple photoreduction method, and shows a good potential of the Cu2O NPs modified ZnO NWs for low concentration NO gas sensing.