1. Department of Nanoscale ScienceMax Planck Institute for Solid State Research Heisenbergstrasse 1 70569 Stuttgart Germany
2. National Institute of Materials Physics Atomistilor Strasse, No. 405A 077125 Magurele Romania
3. Present address: Institute of Applied PhysicsTechnische Universität Braunschweig Mendelssohnstrasse 2 38106 Braunschweig Germany
4. Institution: Donostia International Physics Centre Paseo Manuel de Lardizabal 4 20018 Donostia—San Sebastián Spain
5. Present address: University of LiverpoolDepartment of Chemistry Crown Street Liverpool L69 7ZD UK
6. Department of Organic ElectronicsMax Planck Institute for Solid State Research Heisenbergstrasse 1 70569 Stuttgart Germany
7. Present address: University of CambridgeCavendish Laboratory J J Thomson Avenue Cambridge CB3 0HE UK
8. SUPASchool of Physics and AstronomyUniversity of St Andrews North Haugh St Andrews KY16 9SS UK
9. Nanosurf LabInstitute of Physics of the Czech Academy of Science Cukrovarnicka 10 16253 Praha 6 Czech Republic
10. UPV/EHU and Material Physics Center (MPC)Centro Mixto CSIC-UPV/EHU Paseo Manuel de Lardizabal 5 20018 Donostia—San Sebastián Spain
11. Institute of Applied PhysicsTechnische Universität Braunschweig Mendelssohnstraße 2 38106 Braunschweig Germany
12. Institut de PhysiqueÉcole Polytechnique Fédérale de Lausanne (EPFL) EPFL SB IPHYS-Direction Bâtiment PH, Station 3 1015 Lausanne Switzerland