Geometry and chiral symmetry breaking of ripple junctions in 2D materials

In bulk crystals dislocation junctions underlie the physics of strain hardening. In two-dimensional (2D) crystals, dislocations take the form of surface ripples owing to the ease of bending and weak vdW adhesion of the atomic layers. Here we report that a ripple junction in 2D crystals features distinct morphologies and functions from their bulk counterparts. Our atomistic simulations show that a ripple junction in monolayer graphene exhibits four-fold symmetry. Upon biaxial compression the ripple junction undergoes helical instability, forming a helix with a random orientation. Differently, in-plane shear separates the junction into two individual ripples. We further demonstrate that the helicity of the junction can be controlled by a shear-compression loading sequence or the adsorption of a single chiral molecule at the junction. Shear-controlled helicity forms the basis for mechanical transduction and electro-opto-mechanical coupling, while adsorbate-driven helicity – which imparts the chirality of a single molecule onto a helical distortion pattern of the host 2D layer – has ramifications for sensing and chiral control.