Interface disorder probed at the atomic scale for graphene grown on the C face of SiC

We use aberration-corrected scanning transmission electron microscopy, electron energy-loss spectroscopy, atomic force microscopy, and the density functional theory to study the structural and electronic characteristics of graphene grown on the C face of SiC. We show that for high growth temperatures the graphene/SiC(0001¯) interface is dominated by a thin amorphous film which strongly suppresses the epitaxy of graphene on the SiC substrate. This film maintains an almost fixed thickness regardless of the number of the overlying graphene layers, while its chemical signature shows the presence of C, Si, and O. Structurally, the amorphous area is inhomogeneous, as its Si concentration gradually decreases while approaching the first graphene layer, which is purely sp2 hybridized. Ab initio calculations show that the evaporation process and the creation of Si vacancies on the C face of SiC strongly enhance the surface disorder and designate defect areas as preferential sublimation sites. Based on these features, we discuss differences and similarities between the C-only buffer layer that forms on the Si face of SiC and the thicker C-Si-O amorphous film of the C face.