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, important fundamentals such as the structure of intercalated phases, locations of intercalated atoms, thermodynamic preference for intercalation, and intercalation pathways for this system have not yet been understood conclusively. In this work, 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 three-dimensional Pb islands. We also find that initiation of intercalation either by individual Pb atoms directly penetrating graphene or by hopping under a static graphene step edge is ener-getically 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.

Automated summary

SiC-supported graphene intercalated by a two-dimensional Pb monolayer is a promising platform for spintronic applications. The thermodynamic stability of this structure has been confirmed in recent experiments. However, the details of intercalated phases, location of atoms, thermodynamic preference, and intercalation pathways are still not fully understood. In this study, extensive density functional theory calculations were conducted to investigate the thermodynamics and kinetics of Pb intercalation on graphene/SiC(0001). The results suggest that intercalation of complete Pb layers in the gallery is strongly favored over other configurations, and more complex intercalation pathways are involved.