Characterization of Bismuth Ferrite BiFeO3 and Barium Titanate BaTiO3 Films
thesisposted on 09.12.2012 by Jiri Kabelac
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The subject of this thesis is to examine properties of Bismuth Ferrite BiFeO3 (BFO) and Barium Titanate BaTiO3 (BTO) on different substrates, namely SrTiO3 (STO) and Si(001). Unfortunately, due to technical difficulties after certain time period, only a deposition on SrTiO3 was achieved. Both BiFeO3 and BaTiO3 are deposited in molecular beam epitaxy chamber (MBE). Characterization of the films consists of X-ray scans, Rutherford Backscattering, measuring an index of refraction and thickness by an optical method, and electronic measurements as capacitance and relative permittivity. Due to incompatibility of the deposited chromium with the perovskite films, the relative permittivity is in single digits and the other electronics measurements are not performed. The films are grown with different thickness and processing parameters as effusion and substrate temperatures. It is found that if the ratio of metals is kept close enough to 1.0, the BFO film grows epitaxially for a range of growth rates, from 0.371 to 4.644 Å min.-1, despite of the amount of oxygen. The lattice parameter in <001> direction is bigger than 4.02 Å but except in one experiment. The optical methods reveal that there is a tendency the more epitaxial film, the higher the index of refraction and the smaller difference of the index of refraction measured by the polarizing spectrometer and by the Fresnel scan, which is almost always smaller. The index varies from 1.934 to 3.162. Another interesting fact is that the 2theta-omega scan should be done twice, with the sample rotating by 90°, to see whether the scan consist of the same number of peaks. The difference is probably because the film is not close enough to cubic and the X-ray scan is a 3-D problem. The BTO films are more consistent than BFO films. When it is possible to determine the chemical composition via RBS, then the film is either epitaxial or twinning. The lattice parameter is smaller than for bulk but almost identical to the lattice parameter of the STO substrate. The index of refraction is smaller than for bulk and without the imaginary part.