Edge dominated electronic properties of MoS2/graphene hybrid 2D materials: edge state, electron coupling and work function

The binding pattern, electronic properties and work function of MoS2 nanostructures stacked on a graphene substrate have been studied through density functional theory calculations. Three MoS2 dimensionalities have been considered: edge-free monolayer, one-dimensional nanoribbon and zero-dimensional quantum dot (QD). Our results clearly reveal the importance of MoS2 edges in regulating the binding strength and interfacial electron coupling. Remarkably, the MoS2 monolayer stacking on graphene is through van der Waals (vdW) attraction with negligible electron coupling, thus the Dirac-cone electronic band dispersion of graphene is totally conserved. As for the MoS2 ribbon and QD, they can form stronger binding (beyond the vdW attraction) with graphene and are robust enough to attract graphene's electrons, resulting in the opening up of a bandgap in graphene. The excess electrons uniformly accumulate at the S-edges of MoS2 structures forming edge states, which are believed to be responsible for the enhanced catalytic activity observed in experiments. It is also found that the edge-free MoS2 stacking on graphene can lower the work function of the complex compared to the two counterparts. Our study highlights the importance of MoS2 dimensionalities in the heterostructure which is important to guide the design of nanostructures with fruitful electronic and chemical properties.