Computational Nanomechanics of Graphene Membranes
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1185-II05-04
Computational Nanomechanics of Graphene Membranes Romain Perriot, Xiang Gu and Ivan I. Oleynik Materials Simulation Lab, University of South Florida, Department of Physics, 4202 East Fowler Avenue,Tampa, Fl 33620, U.S.A. ABSTRACT Molecular Dynamics (MD) simulations of nanoindentation on graphene membranes were performed. The 2-d Young’s modulus of the graphene monolayer was determined as 243 ± 18 N/m and the breaking strength as 41 ± 3 N/m. These values agree reasonably well with recent experimental results [1]. In addition, the simulations allowed us to examine the atomic-scale dynamics of membrane breaking during the nanoindentation, involving formation of an increasing number of lattice defects until membrane is completely broken. The onset of defect appearance allowed us to determine the true elastic limit of graphene and the corresponding yield strength 29 ± 1 N/m which was not accessible experimentally. The defects consist of vacancies and Stone-Wales type defects. Long stable linear chains of sp bonded carbon atoms (carbynes) were observed under the indenter at the advanced stages of indentation. The dynamics of fracture propagation is governed by the shear stresses developed in the sample. INTRODUCTION Graphene is a carbon-based material consisting of a monolayer of covalently bonded carbon atoms arranged in a honeycomb lattice. Since its successful isolation from graphite, the material has drawn attention from the scientific community, due to its remarkable fundamental electronic, optical and magnetic properties as well as its promising applications in nanoelectronic devices [2]. Graphene also exhibits unusual mechanical properties. In particular, Lee et al. [1] reported results of nanoindentation experiments on graphene membranes by an atomic force microscope (AFM) tip. It was found that it has an exceptional breaking strength, making it the strongest material studied so far. This opens up exciting opportunities for mechanical applications of graphene ranging from resonators and pressure sensors to carbon-fiber reinforcements. The goal of this work is to perform computational experiments of nanoindentation of graphene membranes using atomic-scale simulation techniques. Massively-parallel molecular dynamics (MD) simulations allowed us to extend the size of the system, approaching micronsize. More importantly, the mechanical properties of graphene membranes were studied to a level of detail that is difficult or sometimes impossible to obtain in experiment. In particular, the appearance of defects in the course of indentation enabled us to determine the true elastic limit and the corresponding yield strength which was not accessible experimentally. Two subsets of membranes were employed in our simulations. A first subset of smalldiameter membranes was used to identify the most interesting features, thus saving computational time. Once the important physics and regimes were found, they were thoroughly investigated using a large subset of membranes with diameter approaching experimental dimensions
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