Tunable macroscale structural superlubricity in two-layer graphene via strain engineering

Charalampos Androulidakis,Emmanuel N Koukaras,Costas Galiotis,George Trakakis,George Paterakis

doi:10.1038/s41467-020-15446-y

Abstract

Achieving structural superlubricity in graphitic samples of macroscale size is particularly challenging due to difficulties in sliding large contact areas of commensurate stacking domains. Here, we show the presence of macroscale structural superlubricity between two randomly stacked graphene layers produced by both mechanical exfoliation and chemical vapour deposition. By measuring the shifts of Raman peaks under strain we estimate the values of frictional interlayer shear stress (ILSS) in the superlubricity regime (mm scale) under ambient conditions. The random incommensurate stacking, the presence of wrinkles and the mismatch in the lattice constant between two graphene layers induced by the tensile strain differential are considered responsible for the facile shearing at the macroscale. Furthermore, molecular dynamic simulations show that the stick-slip behaviour does not hold for incommensurate chiral shearing directions for which the ILSS decreases substantially, supporting the experimental observations. Our results pave the way for overcoming several limitations in achieving macroscale superlubricity using graphene.

Highlights

Achieving structural superlubricity in graphitic samples of macroscale size is challenging due to difficulties in sliding large contact areas of commensurate stacking domains
It was reported that superlubricity can be achieved at the micron scale when hexagonal boron nitride is sheared over graphite; these 2D crystals have an intrinsic lattice constant mismatch that favours sliding for all directions[18]
As revealed by the Raman spectra recorded under the same conditions, the intensity of the 2D peak of the folded single layer[28,29] is approximately four times higher than that expected from a single layer due to the changes induced to the double-resonance process compared with a single layer

Summary

Introduction

Achieving structural superlubricity in graphitic samples of macroscale size is challenging due to difficulties in sliding large contact areas of commensurate stacking domains. We report direct measurements of the interlayer shear stress in incommensurately stacked bilayer graphenes produced both by mechanical exfoliation of graphite and chemical vapour deposition (CVD) synthesis, supported on a polymer substrate.

Results

Conclusion