Thermodynamics and Kinetics of Pb Intercalation Under Graphene on Sic(0001)

SiC-supported graphene intercalated by a two-dimensional Pb monolayer can provide an appealing platform for spintronic applications. Such a monolayer structure is thermodynamically ultrastable, as observed in recent experiments. However, as important fundamentals, the structure of intercalated phases, locations of intercalated atoms, thermodynamic preference for intercalation, and intercalation pathways for this system have not yet understood conclusively. In this work, the extensive density functional theory calculations are performed to assess Pb intercalation thermodynamics and kinetics under graphene on SiC(0001). We find that intercalation of isolated Pb atoms is strongly disfavored over adsorption on top of graphene. However, intercalation of complete Pb layers in the gallery between SiC and graphene buffer layer is strongly favored over supported Pb monolayers and moderately favored over formation of supported large 3-dimensional Pb islands. We also find that initiation of intercalation either by individual Pb atoms directly penetrating graphene or by hopping under a graphene step edge is energetically prohibitive at experimental temperatures. Consequently, more complex intercalation pathways are operative and further analyzed. We demonstrated that once an intercalated Pb monolayer forms around a graphene step edge, a facile Pb mass transport by Pb vacancy-mediated diffusion can be triggered for continued growth of the intercalated monolayer.