Ilmenite (FeTiO3) is a wide band gap p-type semiconductor with a band gap of 2.54 eV. Nominal valence states of Fe and Ti ions in FeTiO3 are considered to +2 and +4, respectively. However some experimental data suggested the presence of Ti3+ ions in FeTiO3 due to the intervalence charge transfer from Fe2+ to Ti4+ [1]. We have already reported to prepare well-crystallized epitaxial FeTiO3 films by reactive sputtering technique. The prepared films had large oxygen nonstoichiometry up to FeTiO3.5, and which strongly depended on the sputtering conditions [2]. The electronic structure of FeTiO3 films could be influenced by the oxygen nonstoichiometry. In the present study, we will show the structure and electronic properties of both stoichiometric and non-stoichiometric FeTiO3 films with good exitaxity as a function of the preparation conditions.
Sample films were prepared on α-Al2O3(0001) single-crystalline substrates by helicon plasma sputtering with base pressure of 10-7 Pa. An FeTi alloy target was used for the sputter deposition at substrate temperature of between 300 and 800°C. During the sputtering deposition, a small amount of oxygen gas was introduced into the chamber. The oxygen partial pressure during the deposition was monitored in situ by using a quadrupole-mass filter. Deposition rate and thickness of sample films were about 0.1nm/s and 100 nm, respectively. After the deposition the films were examined by x-ray diffraction measurement (XRD), magnetization measurement (VSM), hard x-ray photoelectron spectroscopy (HAXPS), and conversion electron Mössbauer spectroscopy (CEMS).
[1] T. Fujii, M. Yamashita, S. Fujimori, Y. Saitoh, T. Nakamura, K. Kobayashi, and J. Takada, Proc. Int. Conf. Magn. 2006, Kyoto, in press.
[2] T. Fujii, M. Sadai, M. Kayano, M. Nakanishi and J. Takada, Mat. Res. Soc. Symp. Proc. 746, Q6.10 (2003).
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