Morphological, structural and ellipsometric investigations of Cr doped TiO2 thin films prepared by sol–gel and spin coating

Pure and chromium doped titanium dioxide (TiO2) thin films at different atomic percentages (0.5%, 1.3% and 2.9%) have been elaborated on ITO/Glass substrates by sol-gel and spin-coating methods using titanium (IV) isopropoxide as a precursor. The surface morphology of films was investigated by scanning electron microscopy (SEM) and Atomic Force Microscopy (AFM), the structure was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and high resolution transmission microscopy (HRTEM). SEM and HRTEM show homogenous and polycrystalline films. XRD patterns indicate a phase transition from anatase to anatase-rutile leading to expand the absorption band of TiO2 molecules around 520 cm(-1) in FTIR spectra. The optical constants such as the refractive index (n), the extinction coefficient (K) and the band gap (E-g) as well as the film thickness are determined using spectroscopic ellipsometry technique and Fourouhi-Blommer dispersion model. Results show three major changes; (i) the thickness of pure TiO2 layer is 54 nm, which linearly decreases when the layer is doped with chromium and reaches 33 nm for a doping concentration of 2.9%, (ii) the band gap energy (E-g) is also linearly reduced from 3.24 eV to 2.80 eV when the Cr-doping agent increases, and, (iii) a phase transition from anatase to anatase-rutile is observed causing an increase in values of n(lambda) for wavelength greater than 350 nm. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.