Structure of few-layer epitaxial graphene on 6H-SiC(0001) at atomic resolution

Using directly interpretable atomic-resolution cross-sectional scanning transmission electron microscopy, we have investigated the structure of few-layer epitaxial graphene (EG) on 6H-SiC(0001). We show that the buried interface layer possesses a lower average areal density of carbon atoms than graphene, indicating that it is not a graphenelike sheet with the 6 root 3 x 6 root 3R30 degrees structure. The EG interlayer spacings are found to be considerably larger than that of the bulk graphite and the surface of the SiC(0001) substrate, often treated as relaxed, is found to be strained. Discontinuity of the graphene layers above the SiC surface steps is observed, in contradiction with the commonly believed continuous coverage. (C) 2010 American Institute of Physics. [doi:10.1063/1.3517505]