Molecular-Dynamics Modelling of the Tensile Deformation of Helical Nanowires
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Molecular-Dynamics Modelling of the Tensile Deformation of Helical Nanowires K. Shintani and S. Kameoka Dept of ME & Intelligent Sys, Univ of Electro-Comm, 1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan E-mail: [email protected], URL: http://www.shintani.mce.uec.ac.jp/ ABSTRACT Deformations of Au nanowires of helical structures under enforced elongation are addressed by the molecular-dynamics simulation. The embedded-atom method potential is employed for calculating the interaction between Au atoms. Model nanowires of the two kinds of helicities are prepared. Before elongation, a model nanowire is equilibrated at a specified temperature. Then, the Au atoms at one end of the nanowire are translationally moved in the axial direction. The simulation results show that a model nanowire can be elongated to form a single-atom chain of Au atoms under some circumstances. INTRODUCTION Nanomaterials such as carbon nanotubes, semiconductor nanowires, and metallic nanowires have a wide variety of applications in the fields of nanotechnology. Carbon nanotubes are promising as materials not only for opto-electronic devices but also for micro/nanoelectromechanical systems (MEMS/NEMS), probe tips of scanning probe microscopes, nanomanipulators or nanotweezers. Rapid progress of the growth methods of semicondutor nanowires has realized nanowire junctions and nanowire supperlattices which will open the world of nanodevices. Metallic nanowires have also drawn much attention of researchers since a linear strand of gold atoms at a nanocontact between a scanning tunneling microscopic probe and a metal surface was observed [1]. Nanotubes and nanowires are probably applicable to wiring in nanocircuits. Both knowledge of the mechanical properties of nanomaterials and understanding of their deformation mechanisms are essential to realization of all of these applications. Nanowires have some unique properties at nanoscale such as quantized conductance and long bond-length which are not observed for materials at macroscopic scale. Furthermore, suspended Au nanowires were made in an ultra-high-vacuum (UHV) transmission electron microscope (TEM) with the electron beam thinning technique. It was revealed by high-resolution TEM that these nanowires have multi-shell helical structures [2]. It is well known that carbon nanotubes also have such helical structures and that they are metallic or semiconducting depending on the chirality. Similarly, metallic nanowires are expected to have interesting physical properties due to their chirality. Atomistic simulations using the ab initio scheme and tight-binding potential were also performed to investigate the mechanical properties and formation mechanisms of Au nanowires [3,4]. Such simulations showed that the bond strength of Au nanowires is about twice that of bulk Au, and that single-atom chains appear before nanowires break. However, the nanowire models in these computations have no helical structures. The effect of helicity on the mechanical properties of nanowires remains unknown. In thi
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