1. Institute
for Molecules and Materials, Radboud University of Nijmegen, 6525 AJ Nijmegen, The
Netherlands
2. School of Physics & Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
3. Institute for Microelectronics Technology, 142432 Chernogolovka, Russia
4. Departamento de Física, Universidade do Minho, P-4710-057, Braga, Portugal
5. Graphene Research Centre and
Department of Physics, National University of Singapore, 2 Science Drive 3, 117542, Singapore
6. Momentive Performance Materials, 22557 West Lunn Road, Strongsville, Ohio
4407