1. Department d'Enginyeria Electrònica
2. Escola d'Enginyeria
3. 08193 Barcelona
4. Spain
5. Centro de Física
6. Universidade do Minho
7. P-4710-057 Braga
8. Portugal
9. Center for Nanostructured Graphene (CNG)
10. Department of Physics
11. Technical University of Denmark
12. 2800 Kongens Lyngby
13. Denmark