1. Photonics
and Optoelectronics Group, Department of Physics and CeNS, Ludwig Maximilians University Munich, Amalienstraße 54, 80799 Munich, Germany
2. Nanosystems Initiative
Munich, Schellingstraße 4, 80799 Munich, Germany
3. Department
of Chemistry and Center for Integrated Protein Science, Ludwig Maximilians University Munich, Butenandtstraße 5-13, 81377 Munich, Germany