Self-assembly of graphene ribbons by spontaneous self-tearing and peeling from a substrate

The controllable self-assembly of graphene ribbons on a substrate is shown, demonstrating an effect which could be applied to patterning and actuating devices made from two-dimensional materials. Adding a new dimension to monolayer graphene More than twenty years ago it was envisioned that graphene could be folded and cut into useful forms as a kind of nanoscale origami. In this issue James Annett and Graham Cross describe a system in which single-layer graphene can reorganize itself into three dimensions by a process of folding, sliding and tearing. When a small flap of graphene sheet is folded over to touch itself, it spontaneously starts to slide, tearing into a ribbon-like strip in the process. On removal of a kinetic barrier, the two-dimensional material can coalesce into its more familiar three-dimensional, layered form. The driver for this peeling phenomenon is a thermodynamic mechanism that is robust enough to work over large areas even in air at room temperature. The findings hold promise as a novel mechanism to mechanically actuate two-dimensional materials as well as a new way of assembling them into complex three-dimensional architectures. Graphene and related two-dimensional materials have shown unusual and exceptional mechanical properties 1 , 2 , 3 , with similarities to origami-like paper folding 4 , 5 and kirigami-like cutting 6 , 7 demonstrated. For paper analogues, a critical difference between macroscopic sheets and a two-dimensional solid is the molecular scale of the thin dimension of the latter, allowing the thermal activation of considerable out-of-plane motion. So far thermal activity has been shown to produce local wrinkles in a free graphene sheet that help in theoretically understanding its stability 8 , for example, and give rise to unexpected long-range bending stiffness 6 . Here we show that thermal activation can have a more marked effect on the behaviour of two-dimensional solids, leading to spontaneous and self-driven sliding, tearing and peeling from a substrate on scales approaching the macroscopic. We demonstrate that scalable nanoimprint-style contact techniques can nucleate and direct the parallel self-assembly of graphene ribbons of controlled shape in ambient conditions. We interpret our observations through a simple fracture-mechanics model that shows how thermodynamic forces drive the formation of the graphene–graphene interface in lieu of substrate contact with sufficient strength to peel and tear multilayer grap