Graphene is an allotrope of carbon consisting of a single layer of atoms arranged in a hexagonal lattice nanostructure.   The name is derived from "graphite" and the suffix -ene, reflecting the fact that the graphite allotrope of carbon contains numerous double bonds. Graphene is a flat one-atom thick sheet of sp2 carbon atoms densely packed in a honeycomb crystal lattice structure.    It is the basic structural element for graphite, carbon nanotubes, and fullerenes.