The Initiation of Graphene Growth on SiC(0001)-6H

We have studied the evolution of surface morphology on SiC(0001)-6H during annealing at temperatures up to 1250 C using low-energy electron microscopy (LEEM). Surface roughness is dominated by the formation of deep pits or canyons. We show that the canyons form because of the stability of the 6$\surd $3 $\times $ 6$\surd $3 phase, which pins atomic steps during the decomposition of SiC. The density of pits is ultimately determined by how the 6$\surd $3 phase nucleates. Graphene forms preferentially in these pits, where the step density is highest.