Fabrication of Fe-doped WO3 films for NO2 sensing at lower operating temperature

•Fe-doped nanostructured WO3 films were synthesized using DC sputtering at RT.•The number of film defects was found to increase with increasing Fe concentrations.•The optical bandgap of the film (3.30eV) decreases to 3.15eV after doped with 2.6at% Fe.•The gas sensing of the 2.6at% Fe film to 3–12ppm NO2 at 150°C was significant.•The decrease in the material's band gap and an increase in defects enhanced sensing at lower temperature. Fe-doped tungsten oxide thin films with different concentrations (0–2.6at%) were synthesized on glass and alumina substrates at room temperature using DC reactive sputtering and subsequently annealed at 300°C for 1h in air. The alumina substrate has pre-printed interdigitated Pt-electrodes for gas sensing measurements. The effects of Fe-doping on the film structure and morphology, electronic and optical properties for gas sensing were investigated. The grain size of the different films on the alumina and Pt regions of the substrate vary only slightly between 43 and 57nm with median size of about 50nm. Raman spectra showed that the integrated intensity of WO to OWO bands increases with increasing Fe concentrations and this indicated an increase in the number of defects. From XPS the different concentrations of the Fe-doped films were 0.03at%, 1.33at% and 2.6at%. All the films deposited on glass substrate have shown similar visible transmittance (about 70%) but the optical band gap of the pure film decreased form 3.30eV to 3.15eV after doping with 2.6at% Fe. The Fe-doped WO3 film with the highest Fe concentration (2.6at% Fe) has shown an enhanced gas sensing properties to NO2 at relatively lower operating temperature (150°C) and this can be attributed to the decrease in the optical band gap and an increase in the number of defects compared to the pure WO3 film.