  The 5x5, 6rt(3)x6rt(3)-R30deg, and graphene-covered 6rt(3)x6rt(3)-R30deg
reconstructions of the SiC(0001) surface are studied by scanning tunneling
microscopy and spectroscopy. For the 5x5 structure a rich spectrum of surface
states is obtained, with one state in particular found to be localized on top
of structural protrusions (adatoms) observed on the surface. Similar spectra
are observed on the bare 6rt(3)x6rt(3)-R30deg reconstruction, and in both cases
the spectra display nearly zero conductivity at the Fermi-level. When graphene
covers the 6rt(3)x6rt(3)-R30deg surface the conductivity at the Fermi-level
shows a marked increase, and additionally the various surface state peaks seen
in the spectrum shift in energy and fall in intensity. The influence of the
overlying graphene on the electronic properties of the interface is discussed,
as are possible models for the interface structure.
