Density functional theory calculations revealed that the interfacial 6√3 x 6√3 structure [a warped graphene layer with periodic inclusions of pentagon-hexagon-heptagon (H5,6,7) defects] facilitates a Si diffusion path vertically through the interface layer during epitaxial growth of graphene on SiC(0001). The calculated diffusion barrier was 4.7eV, competitive with Si interstitial diffusion of ∼3.5eV in SiC. Scanning tunnelling microscopy study showed that, for growth in an Ar background, where Si desorption was suppressed and all diffusion channels contribute, graphene films with reduced pit density could be grown on nominally flat SiC substrates. On the other hand, for Si diffusion-limited growth in ultrahigh vacuum, the Si interstitial diffusion was the energetically favorable path where the step edges serve as the necessary outlet toward Si desorption. The much higher density of step edges on vicinal substrates also facilitates the growth of pit-free graphene.

Si Diffusion Path for Pit-Free Graphene Growth on SiC(0001). Sun, G.F., Liu, Y., Rhim, S.H., Jia, J.F., Xue, Q.K., Weinert, M., Li, L.: Physical Review B, 2011, 84[19], 195455