Influence of air annealing on the characteristics of spray-deposited TiO2 thin films and their use as NO2 gas sensors

Titanium dioxide (TiOz) thin films were deposited at 350 °C on thoroughly cleaned substrates using an economical spray pyrolysis process. The film’s structural, morphological, compositional, optical, and electrical properties were examined using XRD, Raman spectroscopy, XPS, FTIR, SEM, EDS, UV-Vis-NIR, and Hall-effect methods. The XRD analysis reveals the anatase nature of the film, with a reduction in peak intensities observed in the sample annealed at 450 °C. The EDX investigation reveals that the film is composed only of Ti and O, which has been confirmed by XPS analysis. FTIR studies confirmed the existence of Ti-O-Ti stretching bonds. The Raman spectra indicate the existence of microstress and anatase phases. SEM images suggest recrystallization during annealing may result in a slight rise in grain size within the crystalline films. The optical study reveals that air annealing is a useful technique to tailor a film’s porosity. The Hall effect study indicates the n-type material conductivity of films. Four distinct target gases-nitrogen dioxide (NOz), carbon dioxide (CO), ammonia (NH.), and hydrogen (H,) were used to study the gas selectivity of the TiO, nanostructured-based metal oxide sensor at various operating temperatures. The sensor exhibits excellent stability, NO2 gas selectivity, and response.
The sensor’s optimum operating temperature was determined to be 250 °C and at this temperature, a response time of 53 s and a recovery time of 125 s were observed for a 5 ppm NO2 gas concentration. The developed sensor may find use in medical and industrial fields.