Mechanics of nanoscale crumpled graphene measured by Atomic Force Microscopy

Abstract

Crumpling profoundly alters the chemical, electrical, mechanical and tribological properties of 2D materials. Structural deformations at these scales can correlate to the local chemical composition, thereby providing a novel method to tune their properties. In order to leverage the unique characteristics of these compact, high surface area structures, it is crucial to understand the mechanical behavior of crumples at the nanoscale and the effect of chemical composition on the crumpling mechanics. Here, we explore the mechanics of crumpled graphene and graphene oxide nanostructures through force-indentation routines using Atomic Force Microscopy. Crumpled graphene and crumpled graphene oxide show a multi-regime power law force deflection response with exponents ranging between 1.2–2.5. Pushing on the crumpled nano-structures induces both reversible and irreversible energy dissipation, which can be observed through changes in the hysteresis between the loading and unloading curves. Describing folding as a structural transformation passing through a metastable transition state with a finite energy barrier, the total energy imparted during force-indentation routines can be quantitatively related to the energy required to bend monolayer graphene. We also demonstrate that the chemical composition of the crumples can strongly influence the energy dissipation, where crumpled graphene consistently dissipated a smaller amount of energy irreversibly compared to crumpled graphene oxide.