A simple spectrophotometric method for determination of the optical constants and band gap energy of multiple layer TiO2 thin films

Using sol–gel processing, TiO2 films have been prepared on microscopic glass slides by dip-coating technique. From X-ray diffractometric (XRD) and X-ray photoelectron spectroscopic (XPS) measurements, it has been confirmed that the deposited films are an anatase form of stoichiometric TiO2. Using either normal incidence transmittance or normal incidence reflectance data, a simple method for determining both film refractive index, n(λ), and film thickness, d, has been proposed for a transparent film on a non-absorbing flat substrate. At same wavelength within visible region, a correlation between TS and TB has been established and verified. TS and TB represent the transmittances of single side and both sides coated films of same thickness, respectively, prepared at identical conditions. Average film thickness per coating at various withdrawal speeds (58–146 mm min−1) has been estimated. An empirical dispersion equation that describes the variation of n(λ) of TiO2 films in the wavelength (λ) range of ∼390–800 nm has been deduced. Band gap energy (Eg) has also been estimated for these films. It has been observed that Eg changes from ∼3.35 to 3.16 eV as the film thickness varies from ∼100 to 300 nm and it does not depend significantly upon film withdrawal speeds in the range 58–146 mm min−1.