TiO2 Based Nanocrystalline Thin Film Gas Sensors Prepared by Ion-assisted Electron beam Evaporation

In this work, we develop TiO₂ based nanocrystalline thin films prepared by ion-assisted e-beam evaporation process. N-type and p-type TiO₂ gas-sensing layers have been deposited by doping with various metal oxide materials including WO₃, MoO₃, and NiO_x. Structural and morphological characterization by means of AFM, SEM, and XRD reveal the thin film is nanocrystalline structure with fine grain of 10-30 nm. NiO_x doping with sufficiently high concentration has proven to produce p-type semiconducting thin film while WO₃ and MoO₃ doping results in typical n-type metal oxide semiconductor. The gas-sensing sensitivity, selectivity, and minimum detectable concentration can be effectively controlled by different dopants and doping concentrations. WO₃ doped TiO₂ thin film showed high sensitivity towards NO₂ acetone and ethylene at lower working temperature. In addition, TiO₂-MO₃ material demonstrated good sensitivity towards CO. While p-type NiOx doped TiO₂ structure show high sensitivity toward ethanol and acetone with distinct behaviors compared to other n-type TiO₂ thin films.