NO2 gas sensing performance of Ag−WO3−x thin films prepared by reactive magnetron sputtering process

We have demonstrated a comparative study of NO2 gas sensing behavior of reactive sputtered growth WO3−x nanocrystalline thin films and its functionalization with Ag nanoparticles (Ag−WO3−x) on Si/SiO2 substrates. X-ray diffraction and transmission electron microscope characterizations demonstrate the formation of polycrystalline monoclinic phase of porous WO3-x thin film. X-ray photoelectron spectroscopy experiments reveal that W6+ charge state has higher concentration compared with that of W4+ and W5+. The Ag−WO3−x films exhibit a sensitivity of about 70% at 10 ppm, while WO3−x films show 12%, measured at 225 °C with same NO2 gas concentration. The response and recovery time are 2 and 3 min. for Ag−WO3−x films, while these for WO3−x films are 3 and 4 min., respectively. This work shows that nano-scale dendritic agglomeration growth of Ag nanoparticles on WO3−x surface can increase active sites for NO2 gas and play an important role in trace-level gas sensing performance.