We use scanning tunneling microscopy/spectroscopy (STM/STS) and low energy electron microscopy (LEEM) to investigate epitaxial graphene grown under vacuum on a 4H-SiC(000-1)-C-face substrate and self-organized parallel graphene ribbons grown in a furnace on a 6H-SiC(000-1) C-face sample covered by a graphite cap. On the vacuum grown graphene, we observed two types of nanostructures including nano-objects and nano-cracks. The results reveal that these nano-objects are located at the graphene/SiC interface leading to electronic interface states. Their height profiles suggest that these objects are made of packed carbon nanotubes confined vertically and forming mesas at the SiC surface. We also find nano-cracks covered by the graphene layer that, surprisingly, is not broken going deep into the crack, with no resulting electronic interface state. Therefore, unlike the above nano-objects, these cracks should not affect the carrier mobility. LEEM has been used to observe the formation of graphene ribbons grown on SiC in a furnace. The morphology and distribution of the ribbons has been examined, and their typical size is about 1 µm wide and 10 µm long.

 

Work supported by Agence National pour la Recherche (ANR) under GraphSiC program