Tailoring NiO Thin Films: Citric Acid-Assisted Synthesis and Cobalt Doping for Enhanced Properties

This study investigates the cobalt doped nickel oxide ssthin films synthesis using a sol-gel method using citric acid as chelating agent combined with spin-coating techniques. The structural, chemical and morphological characteristics of pure NiO, 1%, 3%, 5% and 7% Co doped NiO thin films were examined. Also, effects of annealing temperatures (400 ºC, 500 ºC and 600 ºC) were studied on pure NiO and Co doped NiO. X-ray diffraction (XRD) confirmed a polycrystalline cubic structure with increased crystallinity and the reduced defect states were observed at higher annealing temperatures, particularly at 600 ºC. The UV Visible spectroscopy results revealed the significant transmittance in annealed NiO thin films, with the band gap energy decreasing from 3.72 eV to 2.89 eV as the annealing temperature increased. The X-ray photoelectron spectroscopy (XPS), O 1s spectra revealed the presence of lattice oxygen, surface hydroxyl groups and Ni2O3, with a significant reduction in surface hydroxylation as the annealing temperature increased. Similarly, the Ni 2p spectra showed a decrease in satellite peak intensity, indicating a transition to a more crystalline NiO structure. These results highlight the critical role of annealing temperature and Co doping in tailoring the structural and surface properties of NiO thin films, paving the way for their potential applications in advanced optoelectronic and energy devices.