Multicomponent SnO₂-ZnO-Fe₂O₃ films deposited by sol-gel spin coating technique for propane detection

In this study, films with compositions of 75 mol.%SnO2-15 mol.%ZnO-10 mol%Fe2O3 and 60 mol.%SnO2-20 mol.%ZnO-20 mol%Fe2O3 were deposited onto alumina substrate starting from gels prepared via the sol-gel method, for gas sensing applications. The films were thoroughly characterized using X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), UV-Vis spectroscopy, and electrochemical impedance spectroscopy (EIS). XRD analysis confirmed the films exhibited slight crystallization of SnO₂, while SEM images revealed a homogeneous structure with microcracks, which were more prominent in the film with lower Fe content. The surface chemistry investigations assessed by X-ray Photoelectron Spectroscopy (XPS) showed the presence of Sn⁴⁺, Zn²⁺, and Fe³⁺ ions on the surface, confirming successful incorporation of these in good agreement with XRD and Raman spectroscopy. UV-Vis spectroscopy indicated that the band gap decreased with increasing Fe content, suggesting tunable optical properties. The films were tested for their gas sensing performance using electrochemical impedance spectroscopy, demonstrating sensitivity to propane with a significant response at 400 ppm and optimal performance at 300 °C.