Morphological Evolution of Sub-nanometer SiC Surface Steps upon Graphitization via Electron Channeling

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Epigraphene shares the key electron transport properties of freestanding exfoliated films. However, in contrast to the exfoliated films, new features in the electronic and surface structure appear in epitaxial graphene grown on the (0001) surface of 6H-SiC. The novel electronic properties and the choice of the type of substrate are significant for the design of nonlinear devices and underscores the importance of substrate interactions in epitaxial films. The interaction of epigraphene with the SiC substrate is mediated by a monolayer of C atoms, a so-called ‘‘buffer layer,’’ arranged in a honeycomb lattice, like graphene, but bonded in an sp configuration, with each atom forming a covalent bond to a Si atom beneath. This buffer layer evolves from C-rich, high temperature surface reconstructions of 6H-SiC (0001) upon thermal desorption of Si atoms around T= 1100°C. Annealing to higher temperature (1250°C) results in further desorption of Si, which promotes the formation of a second carbon layer, and deprives the original (topmost) carbon atoms of their covalent bonds to Si atoms, inducing the sp bonding configuration, i.e., into that of a graphene layer.