Molecular-Dynamics Study of the Mechanical Properties of Metallic Nanowires
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Molecular-Dynamics Study of the Mechanical Properties of Metallic Nanowires T. Nakajima and K. Shintani 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 The method of molecular-dynamics is employed to simulate and investigate the deformation of metallic nanowires under tensile strain. The interactions between metallic atoms are calculated by using the embedded-atom method potential. A model nanowire is preliminarily equilibrated at a specified temperature. Then, the uniform uniaxial extension of the nanowire is performed. The thinning process of a metallic nanowire is observed in the sequential snapshots of its morphological change. INTRODUCTION In recently years, nanoscale materials such as fullerenes, carbon nanotubes, and metallic and semiconductor nanowires have attracted much attetion of the researchers in nanotechnology. Nanoscale materials are expected to be applied to not only opto-electronic devices but also MEMS/NEMS (micro/nano-electromechanical systems) and nanomanipulators. Observations of single arrays of metallic atoms in scanning tunneling microscopy studies have provoked prosperity of investigations of nanowires. Nanowires have some unique properties at their nanoscale such as quantized conductance and long bond-length which are not observed for materials at the larger dimensions [1-4]. It can also be guessed that the mechanical behaviors of nanowires under external forces, e.g. their stress-strain relationship and plasticity, are different from the ones of the macroscopic materials. In this simulation study, the deformation characteristics of gold nanowires under uniaxial tension are investigated by the molecular-dynamics (MD) simulation, paying attention to the effects of the elongation conditions such as defomation speed and temperature on the defomation behaviors of nanowires. METHOD OF SIMULATION The simualtion cell is shown in figure 1. Its x,y, and z axes are along the [1 1 0] , [112] , and [111] directions in the fcc crystal structure. The model nanowire at its initial state is constructed by stacking 24 layers of seven gold atoms in the [111] direction. The length of the initial simulation cell is Lz = 56.53 Å. The embedded atom method (EAM) potential [5-7] is adopted to calculate the interactions between gold atoms. The 6-value Gear algorithm is empolyed to integrate the equations of motion. The MD time step is 1.28fs. The simulation procedure is as follows. The periodic boundary condition is imposed in the z direction. Firstly, the temperature of the nanowire is controlled by the velocity-scaling method to attain the specified temperature. This equilibration phase needs 20000 MD steps. After equilibration, the MD calculation in the microcanonical
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Figure 1. Initial configuration of the simulation cell. The nanowire consists of 168 atoms. ensemble is carried out. Next, the simulation proceeds to elongation phase. The model nanowire is elonaga
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