1. Graphene Labs, Istituto Italiano di Tecnologia, Via Morego 30, 16163 Genova, Italy
2. CNI@NEST, Istituto Italiano di Tecnologia, Piazza San Silvestro 12, 56127 Pisa, Italy
3. Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany
4. Institute of Physics, University of Münster, Münster 48149, Germany
5. Institute of Materials Science, Technische Universität Darmstadt, 64287 Darmstadt, Germany