1. Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
2. Institute of Materials Science, Technische Universität Darmstadt, 64287 Darmstadt, Germany
3. AG Physics of Nanosystems, Faculty of Physics, Ludwig-Maximilians-University Munich, Geschwister-Scholl-Platz 1, 80539 Munich, Germany
4. Institute for Quantum Materials and Technologies, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
5. School of Chemical and Biomolecular Engineering, The University of Sydney, Sydney, New South Wales 2006 Australia
6. Institute of Physical Chemistry, Karlsruhe Institute of Technology, 76128 Karlsruhe Germany
7. 1st Institute of Physics, Faculty of Physics, Georg-August-University, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany