▎ 摘 要
Multilayer epitaxial graphene was obtained from a 6H-SiC(001) substrate subjected to a temperature gradient from 1250 to 1450 degrees 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 degrees 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 degrees 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 degrees 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 degrees C was confirmed by first-principles calculations based on the density functional theory.