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