Room temperature NO 2 -sensing properties of hexagonal tungsten oxide nanorods

Hexagonal WO3 nanorods were synthesized through a facile hydrothermal method. The nanorods properties were investigated by scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersive spectroscopy (EDS), and x-ray diffraction (XRD). The NO2-sensing performances in terms of sensor response, response/recovery times and repeatability at room temperature were optimized by varying the heat treatment temperature of WO3 nanorods. The optimized NO2 sensor (400-°C-annealed WO3 nanorods) showed an ultra-high sensor response of 3.2 and short response time of 1 s to 5-ppm NO2. In addition, the 400-°C-annealed sample exhibited more stable repeatability. Furthermore, dynamic responses measurements of annealed samples showed that all the annealed WO3 nanorods sensors presented p-type behaviors. We suppose the p-type behavior of the WO3 nanorods sensor to be that an inversion layer is formed in the space charge layer when the sensor is exposed to NO2 at room temperature.Therefore, the 400-°C-annealed WO3 nanorods sensor is one of the most energy conservation candidates to detect NO2 at room temperature.