Growth dynamics of graphene buffer layer formation on ultra-smooth SiC(0001) surfaces

In this study, the growth process of epitaxial graphene on SiC was systematically investigated. The transition from the initial buffer layer growth to the formation of the first monolayer graphene domains was studied by various techniques: atomic force microscopy, low energy electron diffraction, low energy electron microscopy, Raman spectroscopy, and scanning electron microscopy. The data show that the buffer layer formation goes along with a simultaneous SiC decomposition, which takes place as a rapid step retraction of one specific type of SiC bilayer, in good agreement with the step retraction model. Once the buffer layer coverage is completed, the resulting characteristic regular repeating terrace and step height pattern of one and two SiC bilayers turns out to be very stable against further SiC decomposition. The following initial growth of monolayer graphene domains occurs not homogeneously on all terraces, but interestingly, only on the S2 terraces along the adjacent two bilayer high terrace edges. This behavior is explained by the preferential SiC decomposition at the higher step edges and has some potential for spatial graphene growth control. The faster growth of the graphene layer on the S2 terrace can explain the different nanoscale resistivity values on these terraces measured in an earlier scanning tunneling spectroscopy study [A. Sinterhauf et al., Nat. Commun. 11, 555 (2020)].