Although carbon can form three-dimensional lattices by bonding with four other carbon atoms to form diamond, it can also form two-dimensional sheets (a sheet of paper has only two dimensions, for example) when it bonds to three other carbon atoms. These sheets are called graphene.
Researchers have only recently (2004) been successful in producing sheets of graphene for research purposes, though they all probably had a handy form of graphene in their pocket protectors. Common graphite is the material in pencil lead, and it’s composed of sheets of graphene stacked together. The sheets of graphene in graphite have a space between each sheet, as illustrated in the following figure, and the sheets are held together by the electrostatic force called van der Waals bonding.
Sheets of graphene held together by van der Waals bonding make graphene.
Graphene sheets are composed of carbon atoms linked in hexagonal shapes, as shown in the following figure, with each carbon atom covalently bonded to three other carbon atoms. Each sheet of graphene is only one atom thick and each graphene sheet is considered a single molecule. Graphene has the same structure of carbon atoms linked in hexagonal shapes to form carbon nanotubes, but graphene is flat rather than cylindrical.
A graphene sheet
Excerpted from Nanotechnology For Dummies (2nd edition), from Wiley Publishing