X-ray Diffraction Investigations of TiO 2 Thin Films and Their Thermal Stability
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X-ray Diffraction Investigations of TiO2 Thin Films and Their Thermal Stability Radomír Kužel1, Lea Nichtová1, ZdenČk MatČj1, ZdenČk Hubiþka2, Josef Buršík3 1 Department of Condensed Matter Physics, Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 5, 121 16 Prague 2, Czech Republic 2 Institute of Physics, Academy of Sciences of the Czech Republic, Na Slovance 2, 182 21 Prague, Czech Republic 3 Institute of Inorganic Chemistry of the AS CR, v. v. i., 250 68 Rez 1001, Czech Republic ABSTRACT In-situ laboratory measurements in X-ray diffraction (XRD) high-temperature chamber and detailed XRD measurements at room temperature were used for the study of the thickness, temperature and time dependences of crystallization of amorphous TiO2 thin films. The films deposited by magnetron sputtering, plasma jet sputtering and sol-gel method were analyzed. Tensile stresses were detected in the first two cases. They are generated during the crystallization and inhibit further crystallization that also depends on the film thickness. XRD indicated quite rapid growth of larger crystallites unlike the sol-gel films when the crystallites grow mainly by increasing of annealing temperature. INTRODUCTION Titania is well-known material of great interest because of its low cost, good chemical stability, nontoxicity, mechanical hardness and optical transmittance with high refractive index, and in particular because it is a unique material that connects two distinct photo-induced phenomena: photocatalytic activity and photo-induced superhydrophilicity after UV illumination [e.g 1-5]. However, desired properties are strongly influenced by phase composition (anatase, rutile, brookite), the crystallinity (amorphous, crystalline, nanocrystalline), and/or by their particular microstructure, presence of residual stresses in the films etc. Usually, amorphous films do not have required properties and crystalline or nanocrystalline form is preferred. In principle, these can be prepared by finding of suitable deposition parameters or they can be obtained by annealing of amorphous films. At the same time, because of a need of deposition onto substrates like polymers, lower temperatures are required for the preparation. Therefore, temperature evolution of the film structure and microstructure is of high interest. There has been some attention given to the crystallization of amorphous titania powders and thin films [e.g. 6-8]. In our previous studies [e.g. 9-13], magnetron-deposited nanocrystalline and amorphous films of different thickness were investigated by X-ray diffraction at room temperature and by in-situ measurements in hightemperature chamber. A strong influence of film thickness on composition and crystallization of TiO2 thin films was found. In very thin amorphous films the crystallization is significantly slower than in thicker layers. In this contribution, these results are compared with similar studies of TiO2 films prepared by other methods – plasma jet sputtering and sol-gel technique.
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