Strong Repulsive Lifshitz-van der Waals Forces on Suspended Graphene

TL;DR

This study reveals a strong, intrinsic repulsive Lifshitz-van der Waals force on suspended graphene, measured directly, which significantly impacts wettability and offers new avenues for nanotechnological applications.

Contribution

The paper provides the first direct measurement and theoretical explanation of strong repulsive Lifshitz-vdW forces on suspended 2D materials, highlighting their unique surface interactions.

Findings

Measured repulsive force up to 1.4 kN/m$^2$ at 8.8 nm separation

Revealed intrinsic repulsive surface properties of suspended graphene

Demonstrated potential for molecular actuation and atomic assembly

Abstract

Understanding surface forces of two-dimensional (2D) materials is of fundamental importance as they govern molecular dynamics and atomic deposition in nanoscale proximity. Despite recent observations in wetting transparency and remote epitaxy on substrate-supported graphene, very little is known about the many-body effects on their van der Waals (vdW) interactions, such as the role of surrounding vacuum in wettability of suspended 2D monolayers. Here we report on a stark repulsive Lifshitz-van der Waals (vdW) force generated at surfaces of suspended 2D materials, arising from quantum fluctuation coupled with the atomic thickness and birefringence of 2D monolayer. In combination with our theoretical framework taking into account the many-body Lifshitz formulism, we present direct measurement of Lifshitz-vdW repulsion on suspended graphene using atomic force microscopy. We report a repulsive force of up to 1.4 kN/m$^2$ at a separation of 8.8 nm between a gold-coated AFM tip and a sheet of suspended graphene, more than two orders of magnitude greater than the Casimir-Lifshitz repulsion demonstrated in fluids. Our findings suggest that suspended 2D materials are intrinsically repulsive surfaces with substantially lowered wettability. The amplified Lifshitz-vdW repulsion could offer technological opportunities such as molecular actuation and controlled atomic assembly.