Toughness and strength of nanocrystalline graphene.

Ashivni Shekhawat,Robert O Ritchie

doi:10.1038/ncomms10546

Abstract

Pristine monocrystalline graphene is claimed to be the strongest material known with remarkable mechanical and electrical properties. However, graphene made with scalable fabrication techniques is polycrystalline and contains inherent nanoscale line and point defects—grain boundaries and grain-boundary triple junctions—that lead to significant statistical fluctuations in toughness and strength. These fluctuations become particularly pronounced for nanocrystalline graphene where the density of defects is high. Here we use large-scale simulation and continuum modelling to show that the statistical variation in toughness and strength can be understood with ‘weakest-link' statistics. We develop the first statistical theory of toughness in polycrystalline graphene, and elucidate the nanoscale origins of the grain-size dependence of its strength and toughness. Our results should lead to more reliable graphene device design, and provide a framework to interpret experimental results in a broad class of two-dimensional materials.

Highlights

Pristine monocrystalline graphene is claimed to be the strongest material known with remarkable mechanical and electrical properties
There are conflicting experimental reports whether the strength of polycrystalline graphene is a function of grain size[19,20,21] making the role of simulation and theory more critical. Understanding these statistical fluctuations has become important in light of the fact that graphene synthesized with chemical vapour deposition (CVD) is polycrystalline, and this method is being used to manufacture more than 300,000 m2 of graphene annually[22,23]
A grain boundaries (GB) is an interface between crystalline regions of different lattice orientations and a triple junctions (TJs) is the intersection of three such interfaces, in graphene GBs and TJs are typically composed of pentagon–heptagon defects, known as five to seven defects (Fig. 1)[27,28,29,30]

Summary

Introduction

Pristine monocrystalline graphene is claimed to be the strongest material known with remarkable mechanical and electrical properties. There are conflicting experimental reports whether the strength of polycrystalline graphene is a function of grain size[19,20,21] making the role of simulation and theory more critical Understanding these statistical fluctuations has become important in light of the fact that graphene synthesized with chemical vapour deposition (CVD) is polycrystalline, and this method is being used to manufacture more than 300,000 m2 of graphene annually[22,23]. The traditional theories developed for brittle ceramics with large extrinsic flaws are not applicable for strength fluctuations due to these intrinsic defects. In graphene these defects are GBs and triple junctions (TJs). We believe that the theoretical framework developed here will be applicable to a large class of emerging two-dimensional (2D) materials

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Conclusion