Local wrinkles of van der Waals heterostructures under nanoindentation

Abstract

Probing van der Waals (vdW) heterostructures to characterize their properties, especially the stability and durability is of vital importance due to the weak interactions between two-dimensional materials. However, the wrinkling behavior of vdW heterostructures under nanoindentation is still unclear, which hinders the accuracy and development of probing methods at the nanoscale. Herein, the wrinkles of vdW heterostructures composed of graphene and molybdenum disulfide (MoS2) under indentation are studied through molecular simulation and theoretical analysis. It is found that wrinkles occur when the hoop strain of the upper layer reaches the critical value for the graphene film-single layer MoS2 substrate system. By fitting the force–displacement relationship, we estimate the predicted elastic modulus of the vdW heterostructure, and uncover that the wrinkling phenomena have ignorable effect on the probing results. It is interesting to find a transition from a sinusoidal wrinkling to a period-doubling bifurcation of vdW heterostructures with the increase of indentation depth. What is more, the wrinkling morphology of vdW heterostructures can be tuned through choosing suitable indentation depth, indenter size, upper film size as well as applied pretension. The present findings should be useful for the developing probing methods of vdW heterostructures, and serve as a guide for their blooming applications.