1. Chair for Photonics and Optoelectronics, Department of Physics and Center for NanoScience (CeNS); Ludwig-Maximilians-Universität München; Amalienstrasse 54 80799 Munich Germany
2. Nanosystems Initiative Munich (NIM); Schellingstrasse 4 80799 Munich Germany
3. EMAT; University of Antwerp; Groenenborgerlaan 171 2020 Antwerp Belgium
4. Department of Physics, Chair for Functional Materials; Technische Universität München; James-Franck-Strasse 1 85747 Munich Germany