Effect of annealing on structure, morphology and optoelectronic properties of nanocrystalline CuO thin films

The nanocrystalline CuO thin films were prepared on glass substrates by the sol-gel method. The structural, morphological, electrical and optical properties of CuO thin films, submitted to an annealing treatment in the 400-700 degrees C ranges are studied by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Four Probe Technique and UV-visible spectroscopic. XRD measurements show that all the films are crystallized in the monoclinic phase and present a random orientation. Four prominent peaks, corresponding to the (110) phase (2 theta approximate to 32.70 degrees), (002) phase (2 theta approximate to 35.70 degrees), (111) phase (2 theta approximate to 38.76 degrees) and (202) phase (2 theta approximate to 49.06 degrees) appear on the diffractograms. The crystallite size increases with increasing annealing temperature. These modifications influence the microstructure, electrical and optical properties. The optical band gap energy decreases with increasing annealing temperature. These mean that the optical quality of CuO films is improved by annealing.