Spray-deposited iron oxide thin films for the detection of ammonia at room temperature

Iron oxides are widely used gas-sensing materials to detect toxic gases. Researchers have grabbed much attention across the globe due to its cost-effectiveness in production, simplicity and sensitivity towards different gases. In the present study, we have deposited iron oxide thin films using a low-cost, spray pyrolysis technique at various deposition temperatures ranging from 375 to 425 °C with other optimized deposition conditions. The effect of deposition temperate on morphological, microstructural, optical and gas-sensing properties are systematically investigated. With increasing the substrate temperature, the crystallite size of the films is observed to be decreasing, and the optical bandgap increases from 2.8 to 2.88 eV. From the FESEM investigations, the film deposited at 375 °C exhibits the formation of cuboid-shaped nanocrystals with dense surfaces and uniform grain distribution. The AFM studies show that the films have demonstrated smooth surfaces as the substrate temperature increases. At room temperature, gas-sensing properties of iron oxide films have been performed using a static method towards various gases with different concentrations. Response and recovery times of the iron oxide thin films are determined using a transient response curve. The film deposited at a substrate temperature of 375 °C has shown the best sensitivity towards 1 ppm of ammonia with a response and recovery times of 40 s and 56 s, respectively.