Porous titania films fabricated via sol gel rout – Optical and AFM characterization

Mesoporous titania films of low refractive index ～1.72 and thickness within the range of 57–96 nm were fabricated via sol–gel rout and dip-coating technique on a soda–lime glass substrate. Tetrabutylorthotitanate Ti(OBu)₄ was used as a titania precursor. High porosity and consequently low refractive index were achieved using the polyethylene glycol (PEG 1100) as a template. Based on transmittance, using Tauc’s relations, the optical energy band gaps and the Urbach energy were determined. The research shows that in the fabricated titania films there are two types of optical energy band gaps, connected with direct and indirect electron transitions and brought about by the presence of amorphous and crystalline phase respectively. Based on the quantum size effect, the diameters of nanocrystals versus film thickness were determined. AFM studies of the titania films have demonstrated that there are changes of surface morphology taking place with the change of thickness. We have demonstrated that the surface morphology of titania films has influence on wettability.