  Graphene grown epitaxially on SiC has been proposed as a material for
carbon-based electronics. Understanding the interface between graphene and the
SiC substrate will be important for future applications. We report the ability
to image the interface structure beneath single-layer graphene using scanning
tunneling microscopy. Such imaging is possible because the graphene appears
transparent at energies of 1 eV above or below the Fermi energy. Our analysis
of calculations based on density functional theory shows how this transparency
arises from the electronic structure of a graphene layer on a SiC substrate.
