1. Department of Surface and Plasma Science, Faculty of Mathematics and Physics, Charles University, V Holešovičkách 2, 18000 Prague 8, Czech Republic
2. Chair of Interface Research and Catalysis, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstrasse 3, 91058 Erlangen, Germany
3. Peter-Grünberg-Institut 6, Forschungszentrum Jülich, 52425 Jülich, Germany
4. Department of Chemistry–Ångström Laboratory, Uppsala University, Box 538, 751 21 Uppsala, Sweden
5. Department of Physics, University of Bath, Bath BA2 7AY, United Kingdom
6. Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973, USA