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

Abstract

Titanium dioxide (TiO 2 ) 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 400-5508C. 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 5508C the films on steel show needle-and rod-like particles. X-ray diffraction (XRD) and Raman spectroscopy of the TiO 2 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 TiO 2 films formed at 5508C on all substrates are hydrophobic to water droplets, with contact angles in the range 101-1108. These films become hydrophilic on heating to above 1008C in air, or superhydrophillic when irradiated under 254 nm radiation generating water-contact angles less than 58. Surprisingly, use of TTIP under APCVD on steel substrates without an aerosol form exclusively the anatase form of TiO 2 at 400-5508C, 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 TiO 2 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.

Aerosols: A Sustainable Route to Functional Materials

“…have shown that by changing the solvent mix to include differing proportions of methanol and ethanol, it is possible to deposit rutile TiO 2 at temperatures as low as 500 °C (cf. APCVD where rutile only forms above 750 °C) . By being able to reduce the temperature required to form a particular crystalline phase, this can significantly lower the cost of production and reduce the energy required to synthesise such films.…”

“…APCVD where rutile only forms above 750 8C). [39] By being able to reduce the temperature required to form ap articular crystalline phase, this can significantly lower the cost of production and reduce the energy required to synthesise such films.…”

The Effect of Tween® Surfactants in Sol-Gel Processing for the Production of TiO2 Thin Films

“…The presence of the brookite phase was also observed in the [121], [221] and [203] planes. This mixture of phases is commonly observed in the production of TiO2 derived thin films [2,8], and it is believed that the sol-gel method described herein has resulted in the production of largely amorphous TiO2 thin films which cannot be detected by XRD. For further determination of the TiO2 phase, Raman spectroscopy was used, whereby a typical spectrum is shown in Figure 6.…”

“…Titanium dioxide has been used consistently as the photocatalyst of choice to address a variety of environmental problems, and has been shown to be particularly effective when utilised as a thin film coating, specifically in self-cleaning glass [1], antimicrobial applications [2], and for water-splitting to produce hydrogen [3]. A multitude of approaches are used to produce TiO2 thin films, including sol-gel [4] and hydrothermal routes [5], as well as vapour deposition methods, such as chemical vapour deposition (CVD) [6], physical vapour deposition (PVD) [7] and more recently, aerosol-assisted CVD [8] and electric field assisted CVD [9].…”

Order of magnitude increase in photocatalytic rate for hierarchically porous anatase thin films synthesized from zinc titanate coatings

“…34 It has been previously shown that AACVD can be used to independently synthesize films of zinc oxide from zinc acetate, and titanium dioxide using titanium isopropoxide, both in methanol solution. [35][36] In this work, we will show that by combining both precursors in a single solution in different ratios, it is possible to form films containing all of the known structures of zinc titanate, and crucially also films containing both zinc titanate and zinc oxide. We subsequently show that these mixed ZnO-Zn 2 TiO 4 films can be successfully converted into hierarchically porous thin films of TiO 2 while retaining adhesion and with an increase in accessible surface area.…”