Bond Length and Charge Density Variations within Extended Arm Chair Defects in Graphene

Extended linear arm chair defects are intentionally fabricated in suspended monolayer graphene using controlled focused electron beam irradiation. The atomic structure is accurately determined using aberration-corrected transmission electron microscopy with monochromation of the electron source to achieve ∼80 pm spatial resolution at an accelerating voltage of 80 kV. We show that the introduction of atomic vacancies in graphene disrupts the uniformity of C-C bond lengths immediately surrounding linear arm chair defects in graphene. The measured changes in C-C bond lengths are related to density functional theory (DFT) calculations of charge density variation and corresponding DFT calculated structural models. We show good correlation between the DFT predicted localized charge depletion and structural models with HRTEM measured bond elongation within the carbon tetragon structure of graphene. Further evidence of bond elongation within graphene defects is obtained from imaging a pair of 5-8-5 divacancies.