1. Max Planck Institute for Solid State Research, Heisenbergstrasse 1, 70569 Stuttgart, Germany
2. Department of Chemistry and Center for Nanoscience (CeNS), Ludwig Maximilian University of Munich (LMU), Butenandtstrasse 5-13 (D), 81377 Munich, Germany
3. Institute for Nanoelectronics, Technical University of Munich, Arcisstrasse 21, 80333 Munich, Germany