Investigation performance of NO gas sensors using WO3 nanorod sensing membranes

Tungsten oxide (WO₃) nanorods were grown on WO₃ seed layers using hydrothermal synthesis method as the sensing membranes of nitrogen oxide (NO) gas sensors. To obtain optimal crystalline structure, various sputtering parameters were controlled to deposit 100-nm-thick WO₃ seed layers and then annealed in an oxygen ambience for 1 h at various temperatures. The WO₃ nanorods were grown on the optimal WO₃ seed layers using the hydrothermal synthesis method with various precursor solutions at various temperatures. To obtain the optimal amount of gas adsorption sites provided by the oxygen vacancies on the surface of the WO₃ nanorods, the grown WO₃ nanorods were annealed in a hydrogen atmosphere at various temperatures and for various times. To form p-n heterojunction and catalytic spillover effect, p-type gold-black nanoparticles were deposited on the n-type WO₃ nanorods at approximately 80 K using a vapor cooling condensation system. The gold-black nanoparticles and the associated Au contents were observed and estimated using a high resolution transmission electron microscopy and energy dispersive spectroscopy, respectively. Under the 1-ppm NO concentration and operating temperature of 127.5 °C, the response of 33.25, response time of 52 s, and recovery time of 94 s were obtained. The activation energy of the NO gas sensors was lowered by generating oxygen vacancy and decorating gold-black nanoparticles onto the WO₃ nanorods. Therefore, in addition to improving the response characteristics, both the response time and recovery time were also shortened due to the enhanced adsorption capability and desorption capability of NO molecules.