Effect of annealing temperature on the characteristics and sensing properties of WO3 nanowires

A uniform WO3 nanowire structure was prepared by two-step thermal oxidation method on Si substrate. WO3 nanowires show different morphology and crystal structures after annealing at different temperatures. The influence of annealing temperature on WO3 nanowires was investigated by SEM, TEM and XRD. Higher crystallization property and lower surface state was obtained with higher annealing temperature. The gas sensing properties of the WO3 nanowires with various annealing temperatures to NO2 with the concentration ranging from 1 to 4 ppm were examined at different temperatures ranging from room temperature to 200 °C. The results indicate that WO3 nanowires can greatly lower the working temperature of sensors and sensors based on WO3 nanowires show p-type or n-type sensing behaviors depending on annealing temperatures. Possible sensing mechanism of p-type WO3 nanowires and the influence of annealing temperature on sensing types was explained. This work might supply new ideas about gas sensing mechanisms and open a new way to develop p-type WO3 sensing materials.