1. Department of Photonics Engineering, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.
2. Center for Nanostructured Graphene, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.
3. NanoPhoton - Center for Nanophotonics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.
4. Department of Physics, Technical University of Denmark, 2800 Kgs. Lyngby, Denmark.
5. Department of Physics and NanoLund, Lund University, box 118, 22100 Lund, Sweden.
6. Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, 01328 Dresden, Germany.
7. Department of Applied Physics, Aalto University, 00076 Espoo, Finland.