Effect of annealing temperature on structural, morphological and optical properties of CeO₂ thin films obtained from a simple precursor solution

CeO₂ thin films were obtained starting from a simple precursor solution by the sol–gel technique. The precursor solution was prepared by dissolving cerium nitrate in ethanol with lactic acid as stabilizer at room temperature. The as-deposited films were annealed at different temperatures from 250 to 550 °C, in open atmosphere. The effect of annealing temperature on structural, morphological, and optical properties of the films were studied by X-ray diffraction, UV-vis absorbance spectroscopy, Raman spectroscopy, scanning electron microscopy and atomic force microscopy. The results revealed that the annealing temperature plays an important role for improving film properties. X-ray diffraction shows that all films annealed exhibit fluorite cubic structure and increase in the crystalline size from 4.8 to 18.6 nm as the annealing temperature is increased. Raman spectra show a mode at around 463 cm⁻¹, which is attributed to a symmetrical stretching mode of the Ce-8O vibrational unit. Atomic force microscopy images reveal that CeO₂ films with higher surface roughness as the annealing temperature increases. The UV-vis spectra show that all the films have high optical transmittance, ~75% in the visible region. In addition, an increase of the band gap energy from 2.96 to 3.24 eV is obtained when the annealing temperature was raised.

Fig. a XRD patterns of CeO₂ thin films annealed at different temperatures. b (111) interplanar spacing as a function of AT.