NO 2 gas sensing performance of Ag−WO 3− x thin films prepared by reactive magnetron sputtering process

We have demonstrated a comparative study of NO 2 gas sensing behavior of reactive sputtered growth WO 3− x nanocrystalline thin films and its functionalization with Ag nanoparticles (Ag−WO 3− x ) on Si/SiO 2 substrates. X-ray diffraction and transmission electron microscope characterizations demonstrate the formation of polycrystalline monoclinic phase of porous WO 3- x thin film. X-ray photoelectron spectroscopy experiments reveal that W 6+ charge state has higher concentration compared with that of W 4+ and W 5+ . The Ag−WO 3− x films exhibit a sensitivity of about 70% at 10 ppm, while WO 3− x films show 12%, measured at 225 °C with same NO 2 gas concentration. The response and recovery time are 2 and 3 min. for Ag−WO 3− x films, while these for WO 3− x films are 3 and 4 min., respectively. This work shows that nano-scale dendritic agglomeration growth of Ag nanoparticles on WO 3− x surface can increase active sites for NO 2 gas and play an important role in trace-level gas sensing performance.