Gibaja C., Rodriguez-San-Miguel D., Ares P., Gómez-Herrero J., Varela M., Gillen R., Maultzsch J., Hauke F., Hirsch A., Abellán G., Zamora F. and We thank MINECO (Spain) for financial support through the ?Mar?a de Maeztu? Programme for Units of Excellence in R&D (MDM-2014-0377) and the projects CSD2010-0024, MAT2013-46753-C2-1-P, and -2-P as well as MAT2015-66888-C3-3-R. Co-funding from UE is also acknowledged. The research leading to these results has received partial funding from the European Union's Seventh Framework Programme (604391, ?Graphene Flagship?). Financial support from the Fundaci?n BBVA is gratefully acknowledged. Electron microscopy studies were carried out at the Centro Nacional de Microscop?a Electr?nica, Universidad Complutense de Madrid. We thank J. Garcia for support with the TEM measurements. The computation resources used for the simulations in this work were provided by the North-German Supercomputing Alliance (HLRN, bep00047). J.M. gratefully acknowledges support by the European Research Council (ERC, 259286) and by the SPP 1459 ?Graphene? of the DFG. G.A. thanks the EU for a Marie Curie Fellowship (FP7/2013-IEF-627386).