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Recoverable Slippage Mechanism in Multilayer Graphene Leads to Repeatable Energy Dissipation
Wei, Xiaoding,Meng, Zhaoxu,Ruiz, Luis,Xia, Wenjie,Lee, Changgu,Kysar, Jeffrey W.,Hone, James C.,Keten, Sinan,Espinosa, Horacio D. American Chemical Society 2016 ACS NANO Vol.10 No.2
<P>Understanding the deformation mechanisms in multilayer graphene (MLG), an attractive material used in nanodevices as well as in the reinforcement of nanocomposites, is critical yet challenging due to difficulties in experimental characterization and the spatiotemp oral limitations of atomistic modeling. In this study, we combine nanomechanical experiments with coarse-grained molecular dynamics (CG-MD) simulations to elucidate the mechanisms of deformation and failure of MLG sheets. Elastic properties of graphene sheets with one to three layers are measured using film deflection tests. A nonlinear behavior in the force vs deflection curves for MLGs is observed in both experiments simulations: during loading/unloading cycles, MLGs dissipate energy through a 'recoverable slippage' mechanism. The CG-MD simulations further reveal an atomic level interlayer slippage process and suggest that the dissipated energy scales with film perimeter. Moreover, our study demonstrates that the finite shear strength between individual layers could explain the experimentally measured size dependent strength with thickness scaling in MLG sheets.</P>
High-Strength Chemical-Vapor–Deposited Graphene and Grain Boundaries
Lee, Gwan-Hyoung,Cooper, Ryan C.,An, Sung Joo,Lee, Sunwoo,van der Zande, Arend,Petrone, Nicholas,Hammerberg, Alexandra G.,Lee, Changgu,Crawford, Bryan,Oliver, Warren,Kysar, Jeffrey W.,Hone, James American Association for the Advancement of Scienc 2013 Science Vol.340 No.6136
<P><B>Graphene Staying Strong</B></P><P>Although exfoliated graphene can be extremely strong, it is produced on too small a scale for materials application. Graphene can be produced on a more practical scale by chemical vapor deposition, but the presence of grain boundaries between crystallites apparently weakens the material. <B>Lee <I>et al.</I></B> (p. 1073) show that postprocessing steps during the removal of the graphene sheets can oxidize the grain boundaries and weaken them. If these steps are avoided, the material is comparable in strength to exfoliated graphene.</P>