Ni-Doped CoO Nanocomposite Thin Films: Synthesis and Physical Properties

Background: Cobalt oxide (CoO) thin films have attracted considerable interest for sensing and optoelectronic applications owing to their favorable optical and electrical properties. This study investigates the effect of nickel (Ni) doping on the structural, morphological, optical, wettability, and electrical properties of CoO thin films. Methods: Pure and Ni-doped CoO thin films (1, 2, and 3 wt% Ni) were prepared by spray pyrolysis and deposited onto glass substrates at 440 °C, resulting in thin films with an average thickness of approximately 200 nm. The films were characterized using X-ray diffraction, morphological analysis, optical measurements, water contact angle analysis, and electrical conductivity measurements. Results: X-ray diffraction and morphological analyses revealed irregular structures for both pure and Ni-doped films, with grain size increasing as the Ni content increased. Water contact angle measurements indicated hydrophilic behavior for all films. The optical transmittance reached approximately 85%, while the direct optical band gap varied from 1.98 to 1.90 eV. The extinction coefficient ranged from 0.1 to 3.8 within the wavelength range of 300–1000 nm. Furthermore, the electrical conductivity was strongly influenced by Ni doping. The pure CoO thin films exhibited the highest conductivity, while the Ni-doped films showed lower conductivity values depending on the Ni concentration. Conclusions: Ni doping significantly influences the structural, optical, and electrical properties of CoO thin films. The enhanced conductivity, high transparency, and tunable optical band gap demonstrate the potential of Ni-doped CoO thin films for low-cost sensing and practical optoelectronic applications.