Structure and optical properties of solution deposited TiO2 films

TiO2 films were deposited on silica glass substrates at 60 °C from an aqueous acidic solution of TiCl4. The lattice of the precipitated material was expanded and is believed to have been caused by the incorporation of protons, due to incomplete dehydration. Rietveld refinement revealed that the rutile was nano-sized and that it made up only 29% of the precipitated TiO2, the rest being amorphous TiO2. Particles embedded in the film significantly reduced its transparency. Reasonably transparent films were obtained when the introduction of the suspended substrate was delayed until particles precipitated in solution had grown sufficiently large enough to settle to the bottom of the reactor. The film refractive index determined by the envelope method was 2.4. This is significantly higher than previously reported values for solution deposited TiO2 films and is also comparable to values obtained by vapor deposition methods. The high refractive index was the result of a film packing density that is much higher than previously reported.