Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 75: Oxides and Insulators: Epitaxy and Growth
O 75.7: Vortrag
Donnerstag, 28. Februar 2008, 16:45–17:00, MA 042
Structure of epitaxial cobalt oxide films on Ir(100)-(1×1) — •Daniela Hock, Wolfgang Meyer, Kerstin Biedermann, Matthias Gubo, Lutz Hammer, Stefan Müller, and Klaus Heinz — Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstr. 7, 91058 Erlangen
Epitaxial cobalt oxide films were prepared on unreconstructed Ir(100). Visual LEED shows the resulting films to be of (111) orientation with, dependent on preparation details, either a distorted or ideal hexagonal unit mesh. In the distorted case there is, above 320 K, a (1×1) phase. The ideally hexagonal phase is accompanied by a (2×2) superstructure. In both cases the film thickness prohibits scattering contributions from the iridium substrate.
LEED intensities were taken for both the distorted (1×1) and the undistorted (2×2) phase. They were analysed by TensorLEED using phaseshifts alternatively for ions and neutral atoms. The distorted (1×1) phase turns out to be of the CoO(111) rocksalt structure with, however, substantial layer relaxations. Also, a stacking fault near the surface appears to be essential to get a good fit quality. In contrast to the distorted (1×1) phase, the undistorted (2×2) structure is due to a spinel-type Co3O4(111) surface terminated by an oxygen layer with 1/4 ML Co on top. For both phases convincing comparison between experimental and model intensities is achieved (Pendry R-factor 0.19 and 0.13, respectively). The replacement of ionic by atomic phase shifts results in the same structural parameters within the limits of errors and similar best-fit R-factors.