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O: Fachverband Oberflächenphysik

O 10: Oxides and insulators II

O 10.1: Vortrag

Montag, 23. März 2009, 15:00–15:15, SCH A01

Ultrathin cobaltoxide - cobalt interface films — •Matthias Gubo, Christina Ebensperger, Wolfgang Meyer, Lutz Hammer, and Klaus Heinz — Lehrstuhl für Festkörperphysik, Universität Erlangen-Nürnberg, Staudtstr. 7, 91058 Erlangen

The deposition of 1.75 monolayers of cobalt on the unreconstructed Ir(100)-(1×1) surface at liquid nitrogen temperature and under oxygen-poor conditions leads – after annealing at about 670 K – to a well ordered c(4×2) superstructure.

The crystallographic structure of this phase was determined by quantitative low-energy electron diffraction (LEED) whereby an excellent agreement between experimental and calculated I(E)-curves was achieved (Pendry R-factor: 0.17). The resulting model reveals that the film is made up by two atomic layers whereby the layer above the substrate consists exclusively of cobalt, i.e. is a metallic layer which however is strained due to epitaxial misfit. All oxygen atoms reside in the second, outermost layer. It is similar to a (compressed) rocksalt-type CoO(100) plane, however with cobalt vacancies in a c(4×2) periodic arrangement equivalent to a Co:O stoichiometry of 3:4. This is consistent with atomically resolved STM images, whereby cobalt ions of the oxide layer are imaged. The same two-dimensional c(4×2) oxide can also be grown on thicker cobalt films on Ir(100) by post-oxidation at 320 K. The interface between the ultrathin cobalt oxide and metallic cobalt is possibly relevant for magnetoelectronic devices.