1. Walter Schottky Institut, Physik Department, and Center
of Nanotechnology and Nanomaterials, Technische Universität München, Am Coulombwall 4, Garching, 85748, Germany
2. Nanosystems Initiative Munich (NIM), Schellingstrasse
4, München, 80799, Germany
3. Institute of Semiconductor and Solid State
Physics, Johannes Kepler University Linz, Altenbergerstrasse 69, Linz, 4040, Austria
4. Deparment of Chemistry, Ludwig-Maximilian Universität München, Butenandtstrasse 5-13, München, 81377, Germany
5. Institute
for Advanced Study, Technische Universität München, Lichtenbergstraße
2a, Garching, 85748, Germany