Figure 1
Illustration: Alan Stonebraker

Figure 1: (Left) The Fermi surface of graphene is defined by “Dirac cones.” The bottom cone corresponds to the occupied states and the top cone to unoccupied states. Doping graphene with electrons or holes moves the Fermi level up or down with respect to the point where the cones meet—the “Dirac point.” The Fermi level lies at the Dirac point for the purely undoped case. (Right) Adsorbed molecules of 4F-TCNQ dope a graphene layer grown on top of silicon carbide.