Fabrication of bare and cobalt-doped ZnFe2O4 thin film as NH3 gas sensor with enhanced response through UV-light illumination

This work reports on the deposition of bare and cobalt-doped ZnFe2O4 thin films by chemical spray pyrolysis technique to study ammonia (NH3) gas sensing properties. Colorless and strongly smelling, ammonia (NH3) is readily soluble in water and yields ammonium (NH) ions. These gases mix in the air atmosphere cause climate change, and severely affect human health. Therefore, the detection of NH3 below the exposure limit can avoid the deterioration of human health and environment. Co-doping had a significant effect on surface roughness, surface morphology, crystallite size, and sensitivity at room temperature. Co0.5Zn0.5Fe2O4 film (ZFCO5) exhibited an outstanding response (S = 19) towards 10 ppm NH3 gas at room temperature. Compared to the bare film, the ZFCO5 sensor has an eleven-fold higher gas-detection response value for 10 ppm NH3. This is ascribed to the blended effects of small crystallite size, high surface roughness, oxygen vacancies, and angular shape morphology linked into tiny rods in the ZFCO5 film. The ZFCO5 sensor showed a significant speedup in response/recovery times (102 s/34 s) and good response (S = 25) to NH3 under the UV-light (365 nm) illumination at room temperature. The built-in ZFCO5 gas sensor shows promise for real-time NH3 below threshold level monitoring.