Atomistic study of the mechanical stability of multi-layered graphene nanobridges
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Atomistic study of the mechanical stability of multi-layered graphene nanobridges T. Nakajima and K. Shintani Department of Mechanical Engineering and Intelligent Systems, University of ElectroCommunications, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan ABSTRACT The stability of elongated single- and multi-layered graphene nanoribbons (GNRs) are investigated by molecular-dynamics simulation. In order that GNRs are to be modeled as nanobridges connecting two terminals of electronic devices, the short edges of the GNRs are constrained. The distances between the two constrained edges are gradually increased, and the GNRs are uniaxially strained. The energies and out-of-plane deformations of such uniaxially strained GNRs are examined. The energies of multi-layered GNRs will be lower than those of isolated GNRs because the surface areas of multi-layered GNRs are smaller than the total area of the isolated GNRs. Understanding the relationship between the out-ofplane deformations and strain will lead to the control of the ripple structures of GNRs. INTRODUCTION In recent years, nanoscale structures such as nanotubes, nanowires, nanoflakes, quantum dots, antidots, and nanoparticles, have been hot subjects for interest of researchers, and numerous papers regarding graphene and its related materials are being published nowadays. Graphene is a few atomic layers of graphite which have two-dimensional honeycomb structure. Electronic devices using graphene nanoribbons (GNRs) are being developed. Lin et al. [1, 2] fabricated graphene transistors using single-layer and bilayer GNRs. On designing and assembling GNR devices, vibrations and deformations of GNRs should be taken into account. Meyer et al. [3] observed static ripple structures of free suspended GNRs. Many researchers have addressed the static properties of ripples of GNRs by experimental and theoretical approaches. On the other hand, their vibrational modes and characteristics of propagation are not fully understood yet. Recently, we performed molecular-dynamics (MD) simulations [4] for graphene flakes of various shapes and sizes. It was shown that the equilibrium energies depend on both their shape and edge configuration. Vibrations and bendings of free standing and constrained graphene flakes were also observed. In this study, we focus on the strain and number of layers of GNRs, and clarify their effects on the vibrational characteristics of GNRs. To induce strain in GNRs, the short edges of the rectangular GNRs are moved in their lengthwise directions. We obtain equilibrium structures of single-, double-, and triple-layered GNRs of two edge types on their free sides under strains, and their vibrational characteristics are studied. MODEL AND METHOD OF SIMULATION We prepare single and multilayered graphene sheets. A portion of a graphene sheet is shown in figure 1(a). The hatched region is a unit cell whose lengths in the zigzag (ZZ) and armchair (AC) directions are uZ = 3 aC and uA = 3 aC , respectively. aC is the initial bond length between carbon atoms 1.42 Å. Th n
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