Impact of Bismuth Doping on the Physical Properties of Nanostructured NiO Thin Films Fabricated via Chemical Spray Pyrolysis

This study examines the impact of bismuth (Bi) doping on the structural and optical properties of nickel oxide (NiO) thin films prepared via chemical spray pyrolysis (CSP). XRD analysis confirmed that the films crystallize in a cubic phase with a preferential (111) orientation. The incorporation of Bi enhanced the crystallinity, increasing the crystallite size from 14.12 nm for pure films to 19.70 nm for 4% Bi-doped films, while dislocation density decreased by 36% (from 19.65 × 10¹⁴ to 12.57 × 10¹⁴ lines/m²), indicating a reduction in structural defects. AFM analysis revealed smoother surfaces, with RMS roughness decreasing from 5.87 nm to 3.06 nm, and smaller particle sizes, reducing from 83.71 nm to 55.43 nm, suggesting denser film formation. optically, bismuth doping led to a narrowing of the bandgap from 3.45 eV to 3.35 eV due to impurity-induced states, accompanied by a decrease in visible transmittance with higher bismuth content, both the refractive index and extinction coefficient were reduced, reflecting the modifications in the electronic structure and optical behavior of the NiO thin films.