TiO2 nanostructured films on mica using liquid phase deposition

Liquid phase deposition is a method to grow conformal TiO2 films with good crystallinity on various substrates. The growth depends on the hydrophilicity of the substrate surface and we found that mica is a substrate capable of forming uniform and thick films. Films were grown using an aqueous solution of TiF4 through a hydrolysis–condensation process. We have studied films properties; morphology, porosity and thickness, in terms of growth conditions, i.e. TiF4 concentration, growth temperature, deposition time and pH. The porosity of films was shown to rapidly increase from about 18% to about 25% and remained the same for longer growth times. The growth process of films could be identified by three stages; the initial delay, the fast growth and finally growth saturation. The fast growth showed a first order kinetics and resulted in 0.086 eV activation energy that was attributed to Ti–F hydrolysis reaction. The growth saturation was at a mass thickness of about 500 nm and for low-temperature solutions could not be reached even after 70 h. We observed also a dynamic pH change during the growth, and attributed the saturation of growth to the drop of pH to values where growth speed is negligible.