1. Walter
Schottky Institut and Physik Department, Technische Universität München, Am Coulombwall 4, D-85748 Garching, Germany
2. Institute
for Advanced Study, Technische Universität München, Lichtenbergstrasse
2a, D-85748 Garching, Germany
3. Institute
for Nanoscience, CNR NANO S3, I-41125 Modena, Italy
4. Department
of Applied Physics, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
5. Department
of Chemistry, Ludwig-Maximilians-Universität München, Munich 81377, Germany
6. Department of Physics, Information, and Mathematics, University of Modena & Reggio Emilia, Modena, Italy