The interfacial adhesion of contacting pairs in van der Waals materials

Abstract

The interfacial adhesion of contacting pairs between two adjacent layers of 2D van der Waals (vdW) layered materials and between 2D materials and their supporting substrates are essential for manipulating 2D materials and constructing functional 2D materials incorporated devices. Here, the interfacial adhesion forces and energies of various contacting pairs involving 2D materials and their underlying physical mechanisms are investigated by combining atomic force microscopy (AFM) measurements and density functional theory (DFT) calculations. The distinct adhesion forces are verified by selecting various contacting pairs between a bare or graphene-coated Si tip and tungsten disulfide (WS2) or graphene as the 2D materials. When using the bare Si tip, the adhesion forces between tip and monolayer WS2 or bilayer WS2 are determined as 32.07 nN or 38.20 nN, respectively. The adhesion forces between the graphene-coated Si tip and monolayer WS2 or graphene are 14.80 nN or 12.28 nN, respectively. Furthermore, the in-depth density functional theory (DFT) calculation results indicate that a distinctly different charge transfer contributes to the different magnitude of the adhesion forces. Our findings demonstrate that the interfacial interaction is an intrinsic property and critically dependent on the type of 2D materials, suggesting a potential strategy for distinguishing 2D materials by adhesion forces.