Interfacial and electronic properties of heterostructures of MXene and graphene

MXene-based heterostructures have received considerable interest owing to their unique properties. Herein, we examine various heterostructures of the prototypical MXene $\mathrm{T}{\mathrm{i}}_{3}{C}_{2}{T}_{2}$ ($T=\mathrm{O}$, OH, F; terminal groups) and graphene using density-functional theory. We find that the adhesion energy, charge transfer, and band structure of these heterostructures are sensitive not only to the surface functional group, but also to the stacking order. Due to its greatest difference in work function with graphene, $\mathrm{T}{\mathrm{i}}_{3}{\mathrm{C}}_{2}{(\mathrm{OH})}_{2}$ has the strongest interaction with graphene, followed by ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{\mathrm{O}}_{2}$ and then ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{\mathrm{F}}_{2}$. Electron transfers from $\mathrm{T}{\mathrm{i}}_{3}{\mathrm{C}}_{2}{(\mathrm{OH})}_{2}$ to graphene but from graphene to ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{\mathrm{O}}_{2}$ and ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}{\mathrm{F}}_{2}$, which causes a shift in the Dirac point of the graphene bands in the heterostructures of monolayer graphene and monolayer MXene. In the heterostructures of bilayer graphene and monolayer MXene, the interface breaks the symmetry of the bilayer graphene; in the case of the AB-stacking bilayer, the electron transfer leads to an interfacial electric field that opens up a gap in the graphene bands at the $K$ point. This internal polarization strengthens both the interfacial adhesion and the cohesion between the two graphene layers. The MXene-graphene-MXene and graphene-MXene-graphene sandwich structures behave as two mirror-symmetric MXene-graphene interfaces. Our first-principles studies provide a comprehensive understanding for the interaction between a typical MXene and graphene.