Enhancement of the optically activated NO2 gas sensing response of brookite TiO2 nanorods/nanoparticles thin films deposited by matrix-assisted pulsed-laser evaporation

Brookite titanium dioxide (TiO2) nanorods, synthesized by a surfactant-assisted aminolysis route, were used as precursors for the fabrication of thin films by using the matrix-assisted pulsed-laser deposition (MAPLE) technique. Thin films with controllable thickness were grown on a variety of substrates for different characterizations. High-resolution scanning and transmission electron microscopy investigations evidenced the formation of rough TiO2 films incorporating individually distinguishable nanocrystals with different shapes. Suitable alumina substrates equipped with interdigitated electrical contacts (IDC) and heating elements were used to fabricate gas-sensing devices based on resistive transduction mechanism. Electrical characterization measurements in controlled environment were carried out. Typical gas sensor parameters (such as gas response, sensitivity, stability and detection limit) towards selected oxidizing and reducing gases, namely NO2 and CO, respectively, were extracted in dark condition. Very interesting optically activated enhancement of the response towards NO2 oxidizing gas was achieved in controlled atmosphere upon irradiating the sensing layer with UV light with low energy close to the TiO2 sensing layer band-gap width.