1. Faculty of Physics and Earth Science, Felix Bloch Institute for Solid State Physics, University Leipzig, Linnestrasse 5, D-04103 Leipzig, Germany
2. Erlangen Catalysis Resource Centre (ECRC), Friedrich−Alexander-Universität Erlangen−Nürnberg, D-91058 Erlangen, Germany
3. Physics Department, University Paderborn, D-33098 Paderborn, Germany