1. Chair of Physical Chemistry, Department of Chemistry, Technical University of Munich, Lichtenbergstr. 4, 85748 Garching, Germany
2. Catalysis Research Center, Technical University of Munich, Lichtenbergstr. 4, 85748 Garching, Germany
3. Dipartimento di Scienza dei Materiali, University of Milano-Bicocca, via Roberto Cozzi 55, 20125 Milano, Italy
4. Institute of Physics, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland