Metastable phase formation and structural evolution of epitaxial graphene grown on SiC(100) under a temperature gradient

Multilayer epitaxial graphene was obtained from a 6H-SiC(001) substrate subjected to a temperature gradient from 1250 to 1450?°C. Scanning tunneling microscopy and x-ray diffraction were used to identify the structure and morphology of the surface, from which the formation of a metastable phase was inferred. By a comparison between microscopy and diffraction data, we report the appearance of misoriented Si-doped graphene in cold regions (1250?°C) of the substrate. This metastable phase occurs in domains where silicon sublimation is incomplete and it coexists with small domains of epitaxial graphene. At 1350?°C this phase disappears and one observes complete graphene-like layers (although misoriented), where rotational registry between the underlying epitaxial graphene and additional layers is absent. At 1450?°C the stacking among layers is established and the formation of highly oriented single crystalline graphite is complete. The stability of this Si-rich metastable phase at 1250?°C was confirmed by first-principles calculations based on the density functional theory.