CeO₂ Doping Effects on the Structural and Morphological Characteristics of Sprayed NiO for Enhanced Gas Sensing Applications

In this study, nanostructured nickel oxide (NiO) thin films were deposited on glass substrates using a chemical spray pyrolysis at 350 °C. X-ray diffraction (XRD) analysis confirmed that the as-deposited NiO films showed a trigonal structure with a preferred orientation towards the (200) diffraction peak and a crystal size of 12.8 nm. The CeO2-doped NiO films displayed additional CeO2-diffraction peaks at a comparatively low peak intensity and a smaller crystal size of 4.1 nm at a 7 vol.% doping ratio. The nickel oxide film's topography revealed a uniformly granular surface with an average particle size of 36 nm and a surface roughness of 0.9. CeO2 doping reduced the average particle size to 25 and 10 nm, while increasing the dopant concentration to 5% and 7% raised the average surface roughness to 2.038 nm and 2.285 nm, respectively. Elemental composition results for the as-deposited NiO sample showed high percentages of oxygen and nickel contents, indicating a good material composition. Meanwhile, doping with CeO2 showed an increased percentage of cerium, and decreased the percentages of nickel and oxygen, with a homogeneous distribution of elements in the elemental maps. Microstructure images revealed a homogeneous surface of the nickel oxide film free of cracks with an average particle size of 12.32 nm, while the particle size of the doped films ranged between 9.28 nm and 6.97 nm with the development of a porous surface. The dopant of CeO2 significantly affected the properties of NiO, making the developed films promising candidates for optoelectronic applications and high-performance gas sensors by enhancing their surface activity for catalytic reactions.