Characterization of CuO-Doped SnO2 Thin Films Prepared by Sol–Gel and Dip-Coating: A Multi-Analytical Approach

In the current work, we comprehensively studied focus-doped (5%) SnO2 thin films, using scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoemission spectroscopy (XPS). The films were synthesized via a sol–gel process followed by a dip-coating deposition technique to form three-layered structures. To understand the impact of annealing on the properties of the films, we analyzed samples both without annealing and with annealing at 400°C. Electron backscattering (BS) images revealed distinct differences in surface structures between annealed and non-annealed films. The annealed films exhibited a more uniform and smooth surface with fewer defects, while the non-annealed films showed a network of cracks and delaminations. XRD analysis of the annealed films indicated the formation of SnO2 nanoparticles with an average size of 9 ± 1 nm, verifying the crystallinity and nanometric size of the material with heat treatment. XPS depth profiling demonstrated the presence of a metallic tin (Sn0) layer at the interface of the films. The surface tin film was in mixed oxidation states, involving both Sn4+ and Sn2+. Additionally, the copper within the films was found to exist as Cu2+ and Cu+.