Gas Sensing Performance of Dip-Coated Indium-Doped ZnO Films

This paper reports the novel sensing, morphological, and optical properties of indium (In)-doped ZnO films. A sol–gel dip-coating technique was used to synthesize the samples, and indium (In) in variable concentrations (2.0%, 2.5%, 3.0%, 3.5%) was used as a dopant (samples IZ-1, IZ-2, IZ-3, and IZ-4, respectively). These synthesized samples were analyzed by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV–Vis spectroscopy, and photoluminescence (PL) spectroscopy. Characterization studies revealed that the prepared films were highly crystalline, with a hexagonal wurtzite structure, and possessed good optical properties. FESEM images showed nanoparticle size in the range of 85–124 nm. An optical band gap in the range of 3.20–3.31 eV was obtained by UV–Vis spectroscopy. To determine the potential for use in smart nanoscale devices, synthesized In-doped ZnO was coated onto glass substrate and further characterized for its ability to sense NO₂ gas. These films can play an important role in gas sensing applications. Interestingly, the sensitivity of the prepared films was found to improve with an increase in the volume of NO₂ gas concentration from 2% to 4%, while a subsequent increase to 5–6% volume did not lead to further enhancement of gas sensing response. The maximum response (95.10%) was found at 4% vol of NO₂ gas. Thus the optimal concentration of indium (3.0%) shows a maximum response. The prepared films were found to have a quick response time of 65 s and a fast recovery time of 87 s.