1. NEST, Istituto Nanoscienze-CNR and Scuola Normale Superiore, 56127 Pisa, Italy
2. Department of Physics, Politecnico di Milano, 20133 Milan, Italy
3. Max-Planck-Institut für Polymerforschung, 55128 Mainz, Germany
4. School of Physics and Astronomy, University of Manchester, M13 9PL Manchester, U.K.
5. Catalan Institute of Nanoscience and Nanotechnology (ICN2), BIST & CSIC, Campus UAB, Bellaterra, Barcelona 08193, Spain
6. JARA-FIT and second Institute of Physics, RWTH Aachen University, 52074 Aachen, Germany, EU
7. Center for Nanochemistry, College of Chemistry and Molecular Engineering, Academy for Advanced Interdisciplinary Studies, Peking University, Beijing 100871, China
8. Beijing Graphene Institute, Beijing 100095, P. R. China
9. NanoMat/Q-Mat/CESAM, Université de Liège (B5), B-4000 Liège, Belgium
10. Center for Nanotechnology Innovation IIT@NEST, Piazza San Silvestro 12, 56127 Pisa, Italy
11. ICFO - Institut de Ciències Fotòniques, BIST, Castelldefels, Barcelona 08860, Spain
12. Graphene Laboratories, Via Morego 30, 16163 Genova, Italy
13. ICREA - Institució Catalana de Reçerca i Estudis Avancats, 08010 Barcelona, Spain