Effect of Cu or Ni addition to ZnO nanostructures on their n-butanol sensing performance

Abstract

ZnO nanostructures with two shapes were routinely synthesised using a direct-current heating technique. These structures were coated with metals such as Cu and Ni to enhance the sensor response to n-butanol vapour. The surface modification approach associated with semiconductor materials used in gas sensor applications is essential for improving sensing performance, including the sensor response, selectivity, and stability for specific gases. Previously investigated surface modification approaches mostly involved the addition of noble metals, such as Pd, Pt, and Au. However, these metals are expensive for commercial applications. Herein, surface modification by the addition of non-noble metals is presented as a p–n junction for sensor fabrication. Cu and Ni sputter-coated onto ZnO nanostructures were transformed into CuO and NiO, respectively. The results of the gas-sensing characteristics show that the p–n junction formation of the ZnO–CuO and ZnO–NiO sensors remarkably enhanced the sensor response toward n-butanol. The sensor response of the ZnO–NiO sensor upon exposure to n-butanol at a concentration of 1000 ppm was 1400.0 at a working temperature of 450 °C, whereas that of the ZnO–CuO sensor was 775.9 at the optimum working temperature of 400 °C and an n-butanol concentration of 1000 ppm. Furthermore, these sensors exhibited excellent selectivity toward n-butanol compared to other gases. The sensing mechanism is explained by the large depletion layer width at the boundary of the p–n junction, which improves the sensor response. These results demonstrate a viable approach for manufacturing n-butanol sensors and possibly for constructing a functional active layer in e-nose applications.