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

Abstract

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.