▎ 摘　　要

We have studied the formation of graphene on the Si face of SiC(0001)-6H and -4H using in situ electron microscopy. By imaging the nucleation and growth of the 6 root 3 "buffer layer" during annealing in vacuum we identify key factors responsible for the appearance of deep pits during graphene formation. Pits form because domains of the buffer layer pin decomposing surface steps. Graphene is observed to nucleate in the pits, where the step density is high.