Precursor-directed control of crystalline type in atmospheric pressure CVD growth of TiO₂ on stainless steel

Titanium dioxide thin films were grown onto stainless steel by thermal atmospheric pressure chemical vapor deposition using two different titania precursors, titanium tetraisopropoxide and titanium tetrachloride. It is demonstrated that the use of titanium isopropoxide in a nitrogen carrier gas over the temperature range 450-650 °C results in the growth of anatase at lower temperatures (450-550 °C) and a mixture of anatase and rutile at temperatures between 550 and 650 °C. In contrast, the use of TiCl ₄ in conjunction with ethyl acetate as oxygen source in a nitrogen carrier gas over the temperature range 550-650 °C results in the exclusive growth of rutile. Below 550 °C, little or no growth was observed using TiCl₄/ ethyl acetate. We therefore identify a structure-directing role exerted by the different precursor chemistries, which is discussed in terms of possible differences in the rates of the nucleation and growth processes taking place.