Influence of calcination ambient and film thickness on the optical and structural properties of sol–gel TiO2 thin films

Influence of both calcination ambient and film thickness on the optical and structural properties of sol–gel derived TiO2 thin films have been studied. X-ray diffraction results show that prepared films are in an anatase form of TiO2. Films calcined in argon or in low vacuum (∼2 × 10−1 mbar) are found to be smaller in crystallite size, more transparent at low wavelength region of ∼300–450 nm, denser, have higher refractive index and band gap energy compared to air-calcined films. Scanning electron microscopic study reveals that surfaces of TiO2 films calcined in argon or in low vacuum are formed by densely packed nano-sized particulates. Presence of voids and signs of agglomeration can be seen clearly in the surface microstructure of air-calcined films. In the thickness range ∼200–300 nm, band gap energy and crystallite size of TiO2 films remain practically unaffected with film thickness but refractive index of thinner film is found to be marginally higher than that of thicker film. In this work, it has been shown that apart from temperature and soaking time, partial pressure of oxygen of the ambient is also an important parameter by which crystallite size, microstructure and optical properties of the TiO2 films may be tailored during calcination period.