Aerosol‐Assisted CVD of Titanium Dioxide Thin Films from Methanolic Solutions of Titanium Tetraisopropoxide; Substrate and Aerosol‐Selective Deposition of Rutile or Anatase

Titanium dioxide (TiO2) thin films are synthesized using aerosol‐assisted (AA)CVD of titanium (IV) isopropoxide (TTIP) in methanol. Deposition is carried out on glass, steel, and titanium substrates at 400–550°C. The films produce morphologies that are radically different to those from typical aerosol‐assisted processes, and from the use of TTIP in low or atmospheric pressure (AP)CVD. The films show some substrate‐dependent morphology and properties. In particular at 550°C the films on steel show needle‐ and rod‐like particles. X‐ray diffraction (XRD) and Raman spectroscopy of the TiO2 films show that on steel or titanium substrates only the rutile form can be obtained, whereas on glass either anatase, anatase/rutile mixtures, or rutile can be obtained, depending on substrate temperature. The TiO2 films formed at 550°C on all substrates are hydrophobic to water droplets, with contact angles in the range 101–110°. These films become hydrophilic on heating to above 100°C in air, or superhydrophillic when irradiated under 254 nm radiation generating water‐contact angles less than 5°. Surprisingly, use of TTIP under APCVD on steel substrates without an aerosol form exclusively the anatase form of TiO2 at 400–550°C, whereas use of a methanolic aerosol delivery system for the TTIP forms rutile. Hence use of the methanol aerosol has a controlling influence on the deposition chemistry. The TiO2 thin films are shown to be active photocatalysts using a dye‐ink test, and are also shown to be able to photo‐split water in a sacrificial system to evolve oxygen.