Transparency of Graphene to Solid-Solid van der Waals Interactions

Understanding the transparency of two-dimensional (2D) materials to intermolecular interactions-particularly their ability to transmit van der Waals (vdW) forces-is crucial for applications such as the design of 2D material-based nanofluidic and microelectromechanical systems. However, experimental studies have produced inconsistent and even contradictory conclusions regarding the vdW transparency of 2D materials. Here, we employ colloidal atomic force microscopy with a geometrically well-defined probe to measure pull-off and pull-in forces in a model system: graphene on silicon dioxide (SiO_{2}). Our results reveal that the total vdW force deviates significantly from the naive sum of contributions from graphene and its substrate. Intriguingly, the measured pull-off forces indicate that the effective surface energy of a suspended graphene monolayer can exceed that of its substrate-supported counterpart. Furthermore, our measurements of pull-in forces in substrate-supported systems suggest that graphene of 1-5 layers screens 15%-50% of the intrinsic solid-solid vdW interaction, consistent with Lifshitz theory calculations.