Transmission electron microscopy studies of nanostructured TiO2 films on various substrates

A chemical vapour deposition (CVD) synthetic route to the production of nanocrystalline titanium dioxide has been carefully investigated on various substrates. CVD was performed at a relatively low temperature of 320 °C on KCl crystal, Al foil, KBr pellet and freshly sliced MICA substrates. The influence of substrate material on film formation was studied in order to find a titanium dioxide film with good intercalation properties for an electrode in a dye-sensitized solar cell. Intercalation properties depend on average grain sizes and porosity in nanophased materials. These films were thoroughly characterized with respect to their surface morphology, crystal structure and the phase composition. Transmission electron microscopy (TEM) accompanied by selected area electron diffraction (SAED) was employed for structural characterization of TiO2 films. The studies showed that films deposited on KCl crystal, KBr pellet and MICA are solely composed of an anatase phase whereas in the film deposited onto Al foil, the brookite phase of TiO2 is also present. The structural parameters of anatase were determined using the Rietveld refinement of electron diffraction data. By comparison of anatase lattice parameters with their corresponding bulk values, the significant deviation in values of lattice parameters a and c in anatase phase was observed and attributed to the thin-film features. The average grain size and the grain size distribution obtained by TEM were compared for TiO2 films deposited on different substrates.