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The nature of strength enhancement and weakening by pentagon–heptagon defects in graphene

Yujie Wei (Institute of Mechanics, Chinese Academy of Sciences), Jiangtao Wu (), Hanqing Yin (), Xinghua Shi (), Ronggui Yang (), Mildred Dresselhaus ()

Synthesis, Characterization, and Modeling of Low-Dimensional Nanomaterials

Tue 4:20 - 5:40

Salomon 202

The high strength reported in pristine graphene (Lee et al., Science 321:385(2009)) stimulates great interest in utilizing stretchable graphene (Rogers et al. Nature 477:45(2011)) for biological structures and electronic devices. Current synthesis techniques for large-area graphene result in the appearance of defects such as grain boundaries (GBs) (Huang et al. Nature 469:389(2011)). Although there has been good understanding on how dislocations and GBs influence the strength of three-dimensional polycrystals, the effect of GB defects such as pentagon-heptagon rings in the two-dimensional graphene on its mechanical properties is largely unknown. In this work, we address how and why pentagon-heptagon defects in tilt GBs may enhance or weaken the strength of graphene. First, we have found that it is not just the density of defects that affects the mechanical properties, but also the detailed arrangement of the GB defects. The strengths of tilt GBs are proportional to the square of their tilt angles if the pentagon-heptagon defects are evenly spaced, and the trend breaks down if pentagon-heptagon defects are distributed in other ways. Second, we have found that mechanical failure always starts from the bond shared by hexagon-heptagon rings. We have also developed a theory based on disclination dipole interaction to capture the interaction among hexagon-heptagon defects in two-dimensional graphene, which is capable of quantitatively predicting the observed mechanical behavior through molecular dynamics simulation. Our present work provides fundamental guidance to understand how defects interact in two-dimensional crystals, which is important for utilizing high strength and stretchable graphene for biological and electronic applications. References: Wei, et al. Nature Materials 11, 759-763(2012). Wu & Wei, J. Mech. Phys. Solids, DOI: 10.1016/j.jmps.2013.01.008 (2013).