Titanium dioxide films have many remarkable properties, for example photocatalytic activity and hydrophilicity. However, these properties depend significantly on the crystallinity, phase composition and microstructure of the films. In this study, crystallization of amorphous films with different thickness (50−2000 nm) deposited on glass and silicon substrates was investigated by in-situ isochronal and isothermal annealing at different temperatures and compared with the post-annealing of both amorphous and nanocrystalline films.

The X'Pert Pro diffractometer with MRI high-temperature chamber and parallel beam geometry with Goebel mirror, for texture and stress measurements, the Eulerian cradle and polycapillary were used, respectively.

In-situ measurements were performed at slightly lower temperatures (180 ºC, 220 ºC) than the crystallization temperatures previously found on the post-annealed samples and time dependences of selected XRD profiles were investigated. It was found, that the process can well be described by the modified Avrami equation that is applied to integrated intensities of the diffraction peaks, I = 1-exp[-b(t – t₀)n)], where the exponent n was in the range 2−2.5 and slightly increasing with the film thickness. This may indicate two dimensional character of the crystallite growth. The initial time t₀ of crystallization (non-zero intensity) increases nearly exponentially with the decreasing thickness while the slope b increases significantly for thicker films. Typical time necessary for the crystallization of the whole film volume varied from several hours for thicker layers to about ten days for the thinnest films, for the mentioned temperatures. Fast crystallization of the order of minutes appeared at 230 ºC for thicker films and were higher (290 ºC) for the thin films with the thickness below 100 nm. This confirmed the results obtained on post-annealed films. Weak texture was changing during the crystallization. At the beginning, the crystallites with the (00l) orientation were developed. However, after complete crystallization, the texture was weak except the very thin films (below 100 nm). Significant shifts of diffraction peaks with the temperature were observed and tensile residual stresses were confirmed by the sin²ψ method for different diffraction peaks. They decrease with the increasing film thickness. Line profile analysis indicated the growth of relatively large crystallites (100 nm) already at the beginning of crystallization unlike the films which were deposited as nanocrystalline with the crystallite size of 5-10 nm which remained nanocrystalline to relatively high temperatures (600 ºC).

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