Various methods of graphene synthesis. a, Exfoliated graphene (monolayer, bilayer, and other thick layer) obtained by taping from graphite. b, Graphene flake is grown on Cu foil by CVD. c, Schematic procedure to generate high quality graphene powder obtained from reduced graphite oxide and the electron diffraction pattern. Adapted with permission . d, Images of monolayer graphene on 6H–SiC(0001) for explaining epitaxial growth of graphene. Reproduced with permission . Copyright 2009, Nature Publishing Group.