Sol-gel spin-coated V2O3 thin films for Optical HCl and Iodine gas sensing

Monoclinic V2O3 thin films with different thicknesses were prepared by reducing the initial V2O5 into V2O3 by heating the V2O5 - H2O2 solution in a water bath at ∼80 °C for 30 min and then the obtained sol gel was deposited by spin coating on glass substrates. The films were characterized by XRD, SEM, EDAX, and UV/VIS/NIR spectroscopy. The crystallographic structure, surface roughness Ra, surface topography and morphology, optical, and electrical properties are investigated and discussed. Increasing the film thickness from 269 to 620 nm improves the film homogeneity, reduces the surface roughness and, decreases the resistance from 1.12 x 108 to 3.79 x 10−2 Ω respectively, while the localized state width of V2O3 films increases from 0.23 to 2.44 eV, respectively. The values of the direct band gap of 2.4–1.82 eV and the relatively high average values of the absorption coefficient 1.07 x 104 - 1.64 x 104 cm−1 in the visible spectral range, as well as the positive Seebeck coefficient from 28.57 to 104.3 μ V/ °C for the films are depicted with the film thickness increase.V2O3 thin films were tested as sensors for the reducing HCl and oxidizing iodine gases. Without the assistance of difficult techniques or exposure to other gases, the sensing process was found reversible with short response and recovery times of 3& 1 min and 1 & 1 min in the cases of HCl and iodine target gases, respectively. Both sensors manifest high stability and reusability characteristics.