Synthesis, characterization, and gas-sensing performance of macroporous Zn-doped NiO thin films for ammonia gas detection

Zinc-doped nickel oxide (NiO:Zn) thin films have been synthesized by chemical spray pyrolysis (CSP), then we have studied the structural, morphological, and topographical properties. Thereafter, we have investigated the gas-sensing performance for the prepared films toward a low concentration of ammonia NH3 gas. The structural properties show that all films have a polycrystalline structure of cubic NiO along (111) direction, the crystallinity of thin films was improved by Zn-doping concentrations, and the crystallite size of thin films was decreased; on contrary, the lattice constant, unit cell volume, specific surface area, and Ni–O bond length were increased with increasing Zn-doping concentrations. The morphology of thin films has a macroporous nature with different pore diameters and nanoscopic surface roughness. The gas sensors based on NiO:Zn thin films exhibited a remarkable sensitivity and fast response as well as excellent long-term stability toward a low concentration of NH3 gas. Empirical equations were proposed to predict response/recovery time as a function of some correlated variables and revealed excellent coincidence with the measured values.