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. (c) 2007 Elsevier B.V. All rights reserved.