Thermal treatment effects on the material and gas-sensing properties of room-temperature tungsten oxide nanorod sensors

Room-temperature tungsten oxide sensors were prepared by using a solution containing single-crystalline and monodispersed WO2.72 nanorods with an average 75 nm length and 4 nm diameter. Thermal treatment-dependent gas-sensing characteristics of the sensors were examined for achieving a sensor with good performance. They were explained and discussed with their material properties probed by SEM, XRD, XPS and Raman spectroscopy. Optimized thermal treatment was found to be an annealing process at around 400 °C under the flow condition of inert N2 or Ar gas. This treatment leads to the partial oxidation of nonstoichiometric W5+ states into the fully oxidative W6+ without any noticeable change in morphology or crystalline structure. These changes in material properties result in a great improvement in detection and recovery times with only a slight sacrifice of detection response.