Interface and interaction of graphene layers on SiC(0001) covered with TiC(111) intercalation

It is important to understand the interface and interaction between the graphene layer, titanium carbide [TiC(111)] interlayer, and silicon carbide [SiC(0001)] substrates in epitaxial growth of graphene on silicon carbide (SiC) substrates. In this study, the fully relaxed interfaces which consist of up to three layers of TiC(111) coatings on the SiC(0001) as well as the graphene layers interactions with these TiC(111)/SiC(0001) were systematically studied using the density functional theory-D2 (DFT-D2) method. The results showed that the two layers of TiC(111) coating with the C/C-terminated interfaces were thermodynamically more favorable than one or three layers of TiC(111) on the SiC(0001). Furthermore, the bonding of the Ti-hollow-site stacked interfaces would be a stronger link than that of the Ti-Fcc-site stacked interfaces. However, the formation of the C/Ti/C and Ti/C interfaces implied that the first upper carbon layer can be formed on TiC(111)/SiC(0001) using the decomposition of the weaker Ti-C and C-Si interfacial bonds. When growing graphene layers on these TiC(111)/SiC(0001) substrates, the results showed that the interaction energy depended not only on the thickness of the TiC(111) interlayer, but also on the number of graphene layers. Bilayer graphene on the two layer thick TiC(111)/SiC(0001) was thermodynamically more favorable than a monolayer or trilayer graphene on these TiC(111)/SiC(0001) substrates. The adsorption energies of the bottom graphene layers with the TiC(111)/SiC(0001) substrates increased with the decrease of the interface vertical distance. The interaction energies between the bottom, second and third layers of graphene on the TiC(111)/SiC(0001) were significantly higher than that of the freestanding graphene layers. All of these findings provided insight into the growth of epitaxial graphene on TiC(111)/SiC(0001) substrates and the design of graphene/TiC/SiC-based electronic devices.