1. Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenbergerstrasse 69 A-4040 Linz, Austria
2. Institut für Festkörpertheorie und -optik, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, D-07743 Jena, Germany
3. Solid State Physics, Lund University, Box 118, S-22100 Lund, Sweden
4. Polymer & Materials Chemistry, Lund University, Box 124, S-22100 Lund, Sweden
5. Center for Electron Nanoscopy, Technical University of Denmark, Fysikvej, building 307, DK-2800 Kgs Lyngby, Denmark
6. IEMN, UMR CNRS 8520, BP 60069, Avenue Poincaré, 59652 Villeneuve d’Ascq, France
7. NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, Piazza S. Silvestro 12, I-56127 Pisa, Italy