Epitaxial BiFeO3 films pulsed laser deposited on SrTiO3, Nb:doped SrTiO3, and DyScO3 were studied using variable angle spectroscopic ellipsometry, vacuum ultraviolet ellipsometry, micro-Raman spectroscopy, and x-ray diffraction. The energy band gap of the film deposited on DyScO3 is 2.75 eV, while the one for the film deposited on Nb:doped SrTiO3 is larger by 50 meV. The blueshift in the dielectric function of the BiFeO3 films deposited on Nb:doped SrTiO3 compared to the films deposited on DyScO3, indicates a larger compressive strain in the films deposited on Nb:doped SrTiO3. This is confirmed by Raman spectroscopy and by high resolution x-ray diffraction investigations.
Multiple scattering in bubbly mixture can be studied using a many-body theory, which • principle is able to include any order interactions in a many-body system. In this paper, the theory is first described in an illustrative manner, and then applied to the case of a bubbly mixture. As an initial step, consideration is given to up to second-order interactions of bubbles, and the effective wave number of the average scattered field is derived. The result provides a higher-order correction to previous results that have generally neglected mutual interactions of bubbles. The phase speed and amplitude attenuation of acoustic waves in the mixture are calculated from the effective wave number. Numerical results show that the higher-order correction can be rather significant under certain circumstances. The primary purpose of this paper is to present a relatively simple and systematic approach to such problems as described here. The work can also be extended to include higher-than-second-order interactions, which remains to be the subject of future research. ¸
This paper presents a new approach for calculating sound scattering by slender scatterers. The method is based on the assumption that the sound scattering function can be approximated by superimposing the scattered waves from a series of small adjacent cylindrical elements, with each of these elements scattering sound as though it were part of an infinite straight cylinder of the same radius. Using the Kirchhoff integral theorem, the bistatic scattering function is derived rigorously within the accuracy of the assumption. To validate the approach, the solution is applied to sound scattering by fluid prolate spheroids, for which the exact solution is known. Numerical comparison with the exact solution reveals that the new approach is very versatile; it can predict scattering patterns remarkably comparable to that obtained by the exact solution for a wide range of incident angles. For incidence within approximately Ϯ20°of the broadside direction, the scattering patterns predicted by the new method coincide uniformly with the exact results. Agreement in the absolute scattering amplitude slowly deteriorates as the incidence is tilted away from the broadside aspect. However, the method consistently produces scattering patterns highly correlated to the results from the exact solution; this is potentially useful for target identification based on pattern recognition techniques. The results also show that the new method works better on the whole as the elongation of the target increases. Furthermore, calculation of cross-correlation coefficients indicates that the present method works slightly better for rigid bodies than for weak fluid bodies. The low-frequency scattering by gas-filled spheroids is also considered. It is shown that near resonance the scattering is almost isotropic, in agreement with the prediction of previous simple analytic solution.
Epitaxial thin films of bismuth ferrite, BiFeO3, were deposited by pulsed laser deposition (PLD) on SrTiO3 (100), Nb‐doped SrTiO3 (100) and DyScO3 (110) substrates. Ellipsometric spectra are obtained in the energy range 0.73‐9.5 eV by combining Variable Angle Spectroscopic Ellipsometry (VASE) and vacuum ultraviolet (VUV) ellipsometry with synchrotron radiation. The optical constants of BiFeO3 films were determined by analysing the ellipsometric spectra with a model that describes the optical response of a system consisting of air, film and substrate. The shift towards higher energies of the refractive index and extinction coefficient of the film deposited onto Nb‐doped SrTiO3 as compared with that deposited onto DyScO3 was attributed to a more compressive in‐plane epitaxial strain. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
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