Ethanol sensing enhancement of low-coast sprayed α-Fe₂O₃ films

This work reports the manufacture and the characterization of α-Fe₂O₃ thin and thick films grown on glass substrates at 350 °C using the chemical spray technique and subsequently modified by thermal annealing at 450 °C. The Crystalline structure, the surface morphology and the optical properties of the films were investigated. The decreases of the α-Fe₂O₃ film thickness affect all physical properties by improving the optical, structural and mostly ethanol sensing properties wherein we note an improvement of ethanol response from 4 under 5000 ppm for thick layer to 13 under only 100 ppm for thin layer. We note also for this layer, an improvement of phase purity which is confirmed by the increases of optical bandgap from 2.15 eV to 2.19 eV, with guarding the same preferred direction (104). Under ethanol α-Fe₂O₃ thick films exhibit a transition from n to p-type conductivity whereas thin films exhibit only p-type conductivity, the detection mechanism of this behavior was attributed mainly to grain size effects. (paper)