Elsevier

Surface Science

Volume 601, Issue 18, 15 September 2007, Pages 4479-4483
Surface Science

Fe-doped TiO2 thin films

https://doi.org/10.1016/j.susc.2007.04.139Get rights and content

Abstract

The reactive sputtering technique was used to obtain undoped and Fe-doped TiO2 thin films deposited on glass substrates. At 250 °C substrate temperature, undoped TiO2 films crystallize in a mixed rutile/anatase phase, while Fe-doped films exhibit the rutile phase only. Presence of Fe3+ ions into the TiO2 lattice is suggested by the intensity variation of forbidden 1s  3d transitions between the Ti and Fe K-edges. Ti K-edge EXAFS data are assessed to a mixture of the two kinds of surroundings, a rutile-like crystalline phase, identified also by X-ray diffraction, and a nanosized or amorphous anatase-like surrounding. The local atomic order about Fe atoms is quite different and could be related also to an amorphous phase. The Swanepoel method is used to obtain the dispersion of the refractive index below the interband absorption edge. The dispersion energy, the single-oscillator energy and the coordination number of the Ti atoms are evaluated using the single-oscillator model (Wemple–DiDomenico).

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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