1. Department Chemie and CeNS, Ludwig-Maximilians-Universität, 81377 Munich, Germany
2. Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
3. DFG Center for Functional Nanostructures (CFN), 76031 Karlsruhe, Germany
4. IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598, United States
5. Institut für Materialwissenschaft, Technische Universität Darmstadt, 64287 Darmstadt, Germany