The Strength of Mechanically-Exfoliated Monolayer Graphene

TL;DR

This study investigates the deformation and fracture behavior of mechanically exfoliated monolayer graphene, revealing how defects and flake size influence its strength and failure mechanisms through experimental and simulation approaches.

Contribution

It provides detailed experimental analysis combined with modeling to understand how defects and size affect the mechanical strength of monolayer graphene.

Findings

Graphene strength decreases with increasing flake width.

Failure occurs via flake fracture or interface failure.

Defects significantly reduce graphene's strength from 130 GPa to below 10 GPa.

Abstract

The deformation and fracture behaviour of one-atom-thick mechanically exfoliated graphene has been studied in detail. Monolayer graphene flakes with different lengths, widths and shapes were successfully prepared by mechanical exfoliation and deposited onto poly(methyl methacrylate) (PMMA) beams. The fracture behaviour of the monolayer graphene was followed by deforming the PMMA beams. Through in-situ Raman mapping at different strain levels, the distributions of strain over the graphene flakes were determined from the shift of the graphene Raman 2D band. The failure mechanisms of the exfoliated graphene were either by flake fracture or failure of the graphene/polymer interface. The fracture of the flakes was observed from the formation of cracks identified from the appearance of lines of zero strain in the strain contour maps. It was found that the strength of the monolayer graphene flakes decreased with increasing flake width. The strength dropped to less than 10 GPa for large flakes, much lower than the reported value of 130 GPa for monolayer graphene, thought to be due to the presence of defects. It is shown that a pair of topological defects in monolayer graphene will form a pseudo crack and the effect of such defects upon the strength of monolayer graphene has been modelled using molecular mechanical simulations.