Fe-doped TiO2 thin films
Introduction
Titanium is a 3d transition metal, whose oxides, in thin films, show attractive properties: high transmittance in the visible spectral range, high refractive index, high chemical and thermal durability in hostile environments, etc. Therefore, TiO2 films have a high potential for device applications. One way of controlling its properties is by doping with different atoms. In our previous papers [1], [2], [3], [4] we have reported the influence of doping with Ce, Nb Cr or Fe on the structure, microstructure and, as a consequence, on the optical and electrical properties of titanium oxide films. In this paper we focused on the influence of Fe-doping on the structural properties, local atomic environment, and optical constants of titanium dioxide films.
Section snippets
Experimental
Titanium oxide films were prepared by reactive radio-frequency (RF) sputtering in a conventional 13.56 MHz setup (Huettinger, model PFG 300RF). The films were deposited onto glass substrates, at 250 °C. Fe-doping was achieved using a mosaic structure of Ti and Fe2O3. Oxygen (99.998%) was used as reactive gas and argon (99.9997%) as sputtering gas. The total pressure of the Ar + O2 mixture gas during deposition was set at 0.10 Pa, the partial pressure of O2 being of 0.03 Pa.
For determining the phase
Results and discussion
XRD studies performed on several sets of undoped and Fe-doped TiO2 samples deposited onto glass substrates, reveal that a phase transformation (anatase to rutile) take place by iron doping films [3], [5]. The weight percentage of the rutile phase among the total crystallized phase (i.e. by excluding amorphous contributions which do not reflect in XRD), as calculated using a formula proposed by Spurr and Myers [6], increases by doping from 30% to 100% [5].
Based on EDX measurements [5], the
Conclusions
Reactive RF sputtering was utilized to deposit undoped and Fe-doped TiO2 thin films onto glass substrates. When deposited onto heated substrates, the films present polycrystalline structures. By doping with low concentrations of Fe, the structure changes from mixed anatase/rutile to pure rutile.
From Fe K-edge extended X-ray absorption fine structure, some general conclusions may be summarized as follows: (i) Fe atoms are in 3+ ionization states; (ii) the long-range order about the Fe atoms is
Acknowledgements
This work was supported by the Romanian Ministry of Education and Research through Contract CNCSIS 1148/2006 and Contract CEEX-Matnanech No. 23/2005. EXAFS experiments were possible through the long-term Hasylab project II-05-058. We acknowledge qualified support from Dr. Edmund Welter and Dr. Dariusz Zajac from the Hasylab staff, and scientific cooperation from Prof. Eberhardt Burkel and Dr. Radu Nicula from the University of Rostock in setting up the Hasylab proposal.
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