Effects of rapid thermal annealing on the room-temperature NO2-sensing properties of WO3 thin films under LED radiation

WO3 thin films were sputtered onto alumina substrates by DC facing-target magnetron sputtering. One sample was rapid-thermal-annealed (RTA) at 600 °C in a gas mixture of N2:O2 = 4:1, and as a comparison, another was conventionally thermal-annealed at 600 °C in air. The morphology of both was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and the crystallization structure and phase identification were characterized by X-ray diffraction (XRD). The NO2-sensing measurements were taken under LED light at room temperature. The sensitivity of the RTA-treated sample was found to be high, up to nearly 100, whereas the sensitivity of the conventionally thermal-annealed sample was about five under the same conditions. From the much better selectivity and response-recovery characteristics, it can be concluded that compared to conventional thermal annealing, RTA has a greater effect on the NO2-sensing properties of WO3 thin films.