Effect of CdO ratios on the structural and optical properties of CdO-TiO2 nanocomposite thin films

Nanocomposite CdO-TiO2 thin films have been successfully synthesized via sol-gel and spin coating techniques. The physical properties of the prepared thin films were studied by varying the Cd:Ti ratio (0, 25, 50, 75, and 100%). The structural characterization has been performed by X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). Optical transmission and reflectivity of the obtained films have been studied by UV-Vis-NIR spectroscopy. The obtained results showed that the amount of Cd into the TiO2 matrix can significantly affect the properties of TiO2 thin films; the XRD analysis revealed the appearance of new diffraction planes by increasing the of Cd:Ti ratios, a fact that was also confirmed by the Raman spectra. Effects of incorporated Cd amounts on the crystal phase, crystallite size, surface morphology were investigated. The results showed that most of Cd2+ substituted Ti4+ in the crystal lattice of TiO2 and led to the appearance of the CdTiO3 phase for thin films at a relatively low temperature, which inhibited the growth of crystallite size and suppressed the transformation from anatase to rutile of TiO2 at 450 degrees C. Moreover, formation of different binary and ternary nanocomposite films are justified by varying the Cd:Ti ratios. The optical analysis revealed a high transparency in the visible region, strongly affected by the different Cd:Ti ratios. Incorporated CdO initially increased the bandgap for low values of the Cd:Ti ratio, followed by a bandgap decrease for the highest one.