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The morphology of graphene formed on the (000-1) surface (the C-face) and the(0001) surface (the Si-face) of SiC, by annealing in ultra-high vacuum or in anargon environment, is studied by atomic force microscopy and low-energyelectron microscopy. The graphene forms due to preferential sublimation of Sifrom the surface. In vacuum, this sublimation occurs much more rapidly for theC-face than the Si-face, so that 150 C lower annealing temperatures arerequired for the C-face to obtain films of comparable thickness. The evolutionof the morphology as a function of graphene thickness is examined, revealingsignificant differences between the C-face and the Si-face. For annealing near1320 C, graphene films of about 2 monolayers (ML) thickness are formed on theSi-face, but 16 ML is found for the C-face. In both cases, step bunches areformed on the surface. For the Si-face, layer-by-layer growth of the grapheneis observed in areas between the step bunches. At 1170 C, for the C-face, amore 3-dimensional type of growth is found. The average thickness is then about4 ML, but with a wide variation in local thickness (2 - 7 ML) over the surface.The spatial arrangement of constant-thickness domains are found to becorrelated with step bunches on the surface, which form in a more restrictedmanner than at 1320 C. It is argued that these domains are somewhatdisconnected, so that no strong driving force for planarization of the filmexists. In a 1-atm argon environment, permitting higher growth temperatures,the graphene morphology for the Si-face is found to become morelayer-by-layer-like even for graphene thickness as low as 1 ML. However, forthe C-face the morphology becomes much worse, with the surface displayingmarkedly inhomogeneous nucleation of the graphene. It is demonstrated thatthese surfaces are unintentionally oxidized, which accounts for theinhomogeneous growth.

Comparison of Graphene Formation on C-face and Si-face SiC {0001} Surfaces