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Thick crystalline titania films with grain sizes below 30 nm, as well as nanocrystalline titania particles with sizes below 10 nm, are prepared by a modified CVD method called chemical vapor synthesis (CVS). Pyrolysis of titanium tetraisopropoxide (TTIP) is performed in a hot-wall reactor, in a mixed helium/oxygen atmosphere, using liquid precursor delivery. Film thicknesses of up to 150 lm on silicon (100) substrate materials are achieved. The influence of process parameters (particularly reactor position) on the microstructure and growth rate is examined. Process temperatures, starting at film-forming (CVD) conditions and going up to exclusive particle formation (CVS) are investigated. Grain size, particle size, and crystallographic phases are determined by X-ray diffraction (XRD), Brunauer±Emmett±Teller (BET), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).

Energy-filtered Debye-Scherrer electron powder data have been successfully employed to determine the structure of nanocrystalline anatase (TiO2). The performed structure analysis includes determining the unit cell, space group, solving the structure via direct methods from extracted intensities and refining the structure using the Rietveld technique. The refined structural parameters for space group I4(1)/amd are a = 3.872 (2), c = 9.616 (5) A with titanium at 0.5,0.75,0.375 and oxygen at 0.5,0.75,0.1618 (6). The obtained structure indicates low internal stress as judged from the almost regular geometry of the TiO6 building blocks. Striking resemblance with the anatase structure determined previously by Burdett, Hughbanks, Miller, Richardson & Smith [J. Am. Chem. Soc. (1987). 109, 3639-3646] from neutron diffraction on coarse-grained material gives strong support for the correctness of the structure determined here. The result of the present study shows that the methods originally developed for determining structures from X-ray powder data work equally well with data from electron powder diffraction. This may open the window for structural investigations on the vast number of nanocrystalline materials and thin films whose structures are difficult to determine by X-ray diffraction since they are frequently only available in small quantities.

Thin films (50-200 nm) of SnO 2 TiO 2 were deposited on SiO 2 /(001)Si substrates by RF-sputtering and by molecular beam before they were annealed in vacuum at 200-900°C. In-situ TEM, XRD, SEM, Raman and IR-spectroscopy were used to analyze the structure transformations in the SnO 2 TiO 2 films. In the as-deposited state, the films are amorphous. They crystallize at higher temperatures (starting at about 500°C) forming nanosized grains. The problem of the spinodal decomposition in the SnO 2 TiO 2 system observed earlier at high temperatures is discussed also for low-temperature processing. The stoichiometry of the films of both groups (reactive ion sputtered and high-vacuum e-gun sputtered) is being compared.

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