Berlin 2008 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 17: Poster: Trends in Ion Beam Technology, Magnetism in Thin Films, Functional Oxides, High-k Dielectric Materials, Semiconductor Nanophotonics, Nanoengineered Thin Films, Layer Deposition Processes, Layer Growth, Layer Properties, Thin Film Characterisation, Metal and Amorphous Layers, Application of Thin Films

DS 17.16: Poster

Dienstag, 26. Februar 2008, 09:30–13:30, Poster A

X-ray Absorption Spectroscopy on La0.7Ce0.3MnO3 films: a critical view on valencies — •Christoph Raisch¹, Mathias Nagel¹, Heiko Peisert¹, Thomas Chassé¹, Robert Werner², Dieter Koelle², and Reinhold Kleiner² — ¹Universität Tübingen, Institut für Physikalische Chemie — ²Universität Tübingen, Physikalisches Institut - Experimentalphysik II, 72076 Tübingen, Germany

Strongly correlated electrons, lattice distortions and ordering phenomena lead to a highly interesting interplay between spin, charge and orbital degrees of freedom in the doped perovskite manganites R_1−xA_xMnO₃. Here we report on temperature-dependent XAS and PES measurements on La_0.7Ce_0.3MnO₃ films with varying oxygen content grown by PLD on SrTiO₃. The measurements were in part performed at the soft x-ray beamline WERA at ANKA in surface sensitive total electron yield (TEY) and bulk sensitive fluorescence yield (FY) mode. We studied the O K, the Mn L_2,3 and the Ce M_4,5 edges, both above and below T_C. Significant differences were found between TEY and FY modes even after thorough self-absorption correction. While the surface signal consists solely of tetravalent cerium and a mixture of di- and trivalent manganese, the fluorescence yield measurements show quite some amount of Ce³⁺ and only minor amounts of the Mn²⁺ species. The valency of manganese is directly related to the kind of doping, electrons or holes, and thus the properties of the sample. The films were further examined with PES of the valence band region and the manganese states. The results are discussed with regard to valency and oxygen content.