Synchrotronstrahlungs-Experimente zu Skalierungseffekten und ungewöhnlichen Phasen epitaktischer perowskitischer Schichten

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Thin films of perovskite ferroelectrics are of great interest for basic research as well as for technological applications, as exemplified by nonvolatile random access memories and microelectromechanical systems. Since the properties of ferroelectric materials in reduced dimensions can differ strongly from those of bulk materials, coordinated experimental and theoretical efforts are required to shed light an the relationship of structure and electrical properties in these materials. In this project, theoretical calculations and state-of-the-art experiments using synchrotron radiation and Scanning probe techniques, are brought together for an in-depth comparison of strong, moderate and incipient ferroelectric thin films, exemplified by Pb(ZrO.52Ti0.48)03, BaTiO3 and SrTiO3. The deposition of single-crystalline, epitaxial films of defined thickness on selected substrates will allow a precise control of the strain state of the films. The project aims at: (a) the investigation of the existence of predicted novel ferroelectric phases in thin films (including strain-induced ferroelectricity in SrTiO3) by in-situ x-ray scattering at the relevant temperatures and strains. The simultaneous measurements of electrical and structural properties on samples with SrRuO3 electrodes will allow a full electrical characterization of the ferroelectric state. (b) the polarization switching process in ferroelectric capacitors, studied by simultaneous electrical and x-ray measurements and corresponding theoretical simulations of the dynamic nucleation and growth of domains.