TEM Investigations of Graphene on 4H-SiC(0001)

Transmission Electron Microscopy (TEM) investigations of graphene layers on Si terminated 4H-SiC(0001) are presented. The graphene layers have been grown in a standard method using decomposition of silicon carbide. Two kind of graphene layers have been investigated: 1) grown on Substrates with on-axis orientation, 2) grown on Substrates with 4 degrees and 8 degrees off-axis orientation in respect of c-axis of SiC. In the case of 0 degrees orientation the high resolution TEM micrographs revealed that a thin layer graphene is present: 1-3 monolayers were obtained. It was found that the first carbon layer was about 2 angstrom from the SiC surface. This result indicates that a strong covalent bonds between carbon layer and silicon atoms on the SiC surface exist. The subsequent graphene layers have been found spaced by 3.4 angstrom - similar as in the graphite. That indicates a weak van der Waals bonding between subsequent carbon layers. In the case of 4 degrees and 8 degrees off-axis orientation a thicker layer of about 5-6 monolayers of graphene were obtained. Relative spacings of graphene layers were the same as in the case of on-axis orientation.