Topological Defects in Two Dimensional Crystals: The Stress Buildup and Accumulation

Abstract

Topological defects (TDs) arise in the growth process of twodimensional (2D) materials, as well as aftergrowth heat treatment or irradiation. Our atomistic simulation results show that their mechanical modulation of material properties can be understood qualitatively through the theory of elasticity. We find that the inplane lattice distortion and stress induced by experimentally characterized pentagonheptagon (5|7) pairs or pentagonoctagonpentagon (5|8|5) triplets can be captured by 2D models of dislocations or disclinations, although the outofplane distortion of the lattice reduces stress localization. Lineups of these TDs create nonlocal stress accumulation within a range of ∼10 nm. Interestingly, pileups of 5|7 and 5|8|5 defects show contrasting tensile and compressive buildups, which lead to opposite grain size dependence of the material strength. These findings improve our understandings of the mechanical properties of 2D materials with TDs, as well as the lattice perfection in forming largescale continuous graphene films.