Structure and optical properties of spray deposited Cu–Mn–O thin films for optoelectronic devices

Nanostructured copper manganese oxide (CMO) thin films were prepared by sol-gel method and deposited on glass substrate by spray pyrolysis technique. Different Cu acetate/Mn acetate molar ratios were used to study the effect of Cu acetate on the structure, morphological and optical properties of the deposited films. The prepared films were annealed at 500 °C in air. A polycrystalline structure and mixed oxide phases of copper manganese oxide were confirmed by X-ray diffraction, (XRD). High resolution transmission electron microscopy, (HRTEM), reveals homogenous and very fine grainy structures of the prepared films with a particle size range from 0.5 nm to 2 nm. The optical measurements showed that 93% is maximum optical transmission and the optical band gap of the prepared films was found to be influenced by increasing Cu acetate ratios from 40% to 60% indicating a blue shift. The energy band gap correlated with the allowed direct transition is found to increase from 3.21 eV to 3.58 eV with increasing Cu acetate while the refractive index decreases. The optical investigation by ultraviolet, visible light, and near-infrared, (UV–VIS–NIR), showed a clear absorption peak at 4.28 eV which attributed to the excitonic nature.