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

In this work, we develop TiO
₂
based nanocrystalline thin films prepared by ion-assisted e-beam evaporation process. N-type and p-type TiO
₂
gas-sensing layers have been deposited by doping with various metal oxide materials including WO
₃
, MoO
₃
, 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 WO
₃
and MoO
₃
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. WO
₃
doped TiO
₂
thin film showed high sensitivity towards NO
₂
acetone and ethylene at lower working temperature. In addition, TiO
₂
-MO
₃
material demonstrated good sensitivity towards CO. While p-type NiOx doped TiO
₂
structure show high sensitivity toward ethanol and acetone with distinct behaviors compared to other n-type TiO
₂
thin films.