The role of SiO₂ barrier layers in determining the structure and photocatalytic activity of TiO₂ films deposited on stainless steel

TiO₂ thin films were deposited using two different precursor systems, and their photocatalytic activities studied in the context of the feasibility of self-cleaning added value steel products. SiO₂ layers deposited using flame-assisted CVD were investigated as possible barrier layers to prevent diffusion of substrate components in to the TiO₂ films. The films were characterized by X-ray photoelectron spectroscopy (XPS), sputtered neutral mass spectrometry (SNMS), Raman spectroscopy and scanning electron microscopy (SEM). Photo-activity was characterised by the UV-induced destruction of stearic acid layers. On bare steel growth using titanium tetraisopropoxide yielded anatase, while growth with titanium tetrachloride (with ethyl acetate) yielded rutile. In contrast, on silica coated steels both precursor systems yielded anatase exclusively. The diffusion of components originating from the steel substrates was shown to have a deleterious effect on the photoactivities of the TiO₂ thin films, with this effect being more influential at higher deposition temperatures. However, the presence of the SiO₂ barrier layers significantly reduced ion diffusion into the TiO₂ film and consequently also improved the photocatalytic activity of the samples. While the SiO₂ coated samples gave rise to anatase growth, there is evidence that the thickness of the SiO₂ coating has a direct effect on TiO₂ morphology.