Study of TiO₂, SnO₂ and nanocomposites TiO₂:SnO₂ thin films prepared by sol-gel method: Successful elaboration of variable–refractive index systems

In this research TiO₂, SnO₂ and TiO₂:SnO₂ nanocomposite thin films were fabricated by the sol–gel dip coating technique. The mixture was prepared by varying the molar ratio of SnO₂ to TiO₂, i.e. TiO₂:SnO₂ (9:1), TiO₂:SnO₂ (8:2) and TiO₂:SnO₂ (6:4)). The obtained samples were characterized by means of the Raman microscopy, Scanning Electron Microscopy (SEM), UV–Vis spectrophotometry and m-lines spectroscopy (Prism coupler). Raman analysis shows that pure TiO₂ and SnO₂ thin films are characterized by the vibrational modes of anatase and rutile cassiterite, respectively. Furthermore, the Raman spectra of the TiO₂:SnO₂ nanocomposites show the presence of a mixture of anatase and rutile TiO₂ phases. The SEM images reveal that the morphology is clearly modified with SnO₂ content. The ripples in the transmittance spectra decreased with increasing SnO₂ content. Also, the evolution of the optical band gap seems to be consistent with the Raman analysis. A great attention has been paid to the refractive index measurements by the prism coupler technique. In this way, variable–refractive index systems have been successfully obtained using TiO₂:SnO₂ nanocomposite thin films. (paper)