糖心TV

Among the candidates for multiferroic thin film materials the Bi-based magnetic transition metal perovskites, especially BiFeO₃, are on great interest. Our goal is to explore the optical properties of multiferoica in the range of optical transitions as well as in the frequency range of lattice vibrations. The complex dielectric function of BiFeO₃ and BiCrO₃ thin films grown on different substrates (SrTiO₃, NdGaO₃, DyScO₃. LaAlO₃, LSAT) was determined by evaluation of ellipsometric spectra measured in the energy range of 0.73-9.8 eV by combining Variable Angle Spectroscopic Ellipsometry (VASE) and vacuum ultraviolet (VUV) ellipsometry with synchrotron radiation. By analyzing the absorption onset region, the optical bandgap of BiCrO₃ and of BiFeO₃ films on different substrates was determined. Raman spectroscopy was performed on both polycrystalline and epitaxial thin films of BiCrO₃ in order to get an insight in the phonon spectra and the related structural properties. The temperature dependent Raman measurements indicate a structural phase transition at ~ 400 K which was also confirmed by X-ray diffraction investigations. The epitaxial relation between film and substrate orientation and the symmetry of the films will be discussed based on polarisation dependent Raman measurements.