Dependence of structure and energy band gap on sensing properties of WO3:TeO2 thin films deposited by spray pyrolysis

Abstract

In this paper, the sensing properties of WO3:TeO2 thin films deposited by spray pyrolysis using the oxide precursors with three different molar percentages of WO3 (0.15 M): TeO2 (0.05 M), WO3 (0.1 M): TeO2 (0.1 M) and, WO3 (0.05 M): TeO2 (0.15 M) are studied for before and after annealing at T = 773 K. The CO2 gas sensing properties of the WO3: TeO2 thin films at different molar percentages were investigated and experimental results showed that the sensing response of thin films strongly depends on the structure, morphology, and energy gap. The sensing response of thin films in terms of CO2 concentration for all compounds before and after annealing is linear and also the gradient of the curves increases after annealing. These changes in WO3 (0.15 M): TeO2 (0.05 M) are significant compared to other samples. Influences of TeO2 on the structures and morphology of the binary compounds of WO3: TeO2 thin films were investigated. X-ray diffraction results show that after annealing at T = 773 K, the WO2.92, TeO2, and H2Te2O6 phases were formed. FE-SEM images show that annealing at T = 773 K plays an important role in the morphology of the WO3: TeO2 thin films. The UV–Vis spectroscopy results showed that the bandgap of thin films decreases after annealing at T = 773 K.