Atomistic Simulations of the Deformation and Energetics of Metal Nanowires

Abstract

Nanowires are an exciting class of novel materials that have potential applications in areas including biological sensing, photonics, and electronics. The promise of these future applications relies on the production of nanowires of controlled size, shape, and crystal structure, in reasonable quantities, and further, ultimately requires that the nanowires be mechanically stable in the application environment. This research is aimed at understanding the mechanical behavior of metallic nanowires, through the use of atomistic simulations. At the nanometer scale, where the surface-area-to-volume ratio is substantial, the effects of free surfaces have a primary influence on the physical properties of a material. Surface energy arises from unsatisfied bond coordination at the surface of a solid and results in a surface stress as the surface atoms contract into the bulk of the material to increase their local electron density. The magnitude of surface energy and surface stress is dependent on the orientation of the surface and the compliance of the structure. In bulk materials, the effects of surfaces are negligible; however, at the nanometer scale, surface effects become quite significant. In metallic nanowires, these surface effects strongly influence mechanical properties, and the characteristics of plastic deformation. The mechanical testing of nanowires is precluded by the difficulties of accurately applying and measuring forces on the nanometer scale. For this reason, computational simulations are a primary tool for investigating the mechanical behavior of nanowires. In this work, we have performed atomistic simulations to examine the mechanical response of silver nanowires. We have conducted studies to determine the deformation characteristics of experimentally observed nanowire geometries subjected to tensile and bending loads. We have also developed a technique to probe the energetics of mechanical deformation, in order to elucidate the energetically favored deformation pathways in nanowires. Our results show that nanowires may be tailored for specific mechanical requirements based on geometry and free surface orientation and provide insight to the effect of free surfaces in the mechanical deformation of nanometer scale structures.