1. Institut für Nanotechnologie, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
2. Physikalisches Institut, Karlsruhe Institute of Technology, 76128 Karlsruhe, Germany
3. Department of Mechanical Engineering & Materials Science, Rice University, Houston, Texas 77005
4. Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208-3108
5. Department of Engineering, University of Cambridge, Cambridge CB3 0FA, United Kingdom
6. Institut für Festkörperphysik, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
7. DFG Center for Functional Nanostructures (CFN), 76028 Karlsruhe, Germany
8. Institut für Physikalische Chemie, Karlsruhe Institute of Technology, 76128 Karlsruhe, Germany