Effect Annealing Temperature on Pure and Al-Doped Iron Oxide Thin Films for Formaldehyde Gas Sensing Application

Abstract

The present study employs chemical spray pyrolysis to prepare pure and Al-doped α-Fe2O3 thin films with different aluminium concentrations which were subsequently annealed at 450°C and investigated for the effect of annealing temperature on structural, morphological, optical, chemical, and gas sensing properties. Field emission scanning electron microscopy and X-ray diffraction studies were adapted to examine the morphologies and microstructural properties of the prepared films. All films were polycrystalline with rhombohedral structure, and the (104) plane was confirmed to be the favoured orientation. Deposited thin films were seen to have agglomerated, superimposed sphere-like particles on their surfaces. Raman spectroscopy analysis and XPS were used to examine the film's symmetry and structural characteristics. Pure and Al-doped films' optical band gap increased with the introduction of 5 wt% Al concentration, decreasing further enhancement of Al concentration in the Fe2O3 matrix and the film's formaldehyde sensing capability was examined based on aluminium doping concentration. The film with 10 wt% of Al content showed the most significant sensitivity towards 5 ppm formaldehyde at room temperature. The results of the experiments showed that the gas-detecting capabilities have been significantly enhanced by the optimal content of Al added to the α-Fe2O3 lattice.