Nano-structures developing at the graphene/silicon carbide interface

We use scanning tunneling microscopy and spectroscopy to study defects on epitaxial graphene grown on a 4H-SiC(000-1) C-face substrate. At the graphene/SiC interface, we discover a few isolated small areas covered by nano-objects confined vertically and forming mesas, suggestive of packed carbon nanotubes and leading to electronic interface states. Nano-crack defects are also found at the SiC surface. They are covered with an unbroken graphene layer going deep into the crack showing no electronic interface state, and thus would probably not affect the carrier mobility.