Simulation of Mechanical Elongation and Compression of Nanostructures
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Simulation of Mechanical Elongation and Compression of Nanostructures Sergio Mejía-Rosales1 and Carlos Fernández-Navarro2 1 Facultad de Ciencias Físico-Matemáticas, Universidad Autónoma de Nuevo León, Av. Universidad SN, Cd. Universitaria, San Nicolás de los Garza, N.L, Mexico 66455. 2 Preparatoria No. 25, Universidad Autónoma de Nuevo León. Francisco Villa y Morelos, Ex hacienda el Canadá, Escobedo, Nuevo León, Mexico 66054. ABSTRACT We present a set of Molecular Dynamics simulations of the axial elongation of gold nanowires, and the compression of silver decahedral nanowires by a carbon AFM tip. We used Sutton and Chen multibody potentials to describe the metallic interactions, a Tersoff potential to simulate the carbon-carbon interactions, and a 6-12 Lennard-Jones potential to describe the metal-carbon interactions. In the elongation simulations, gold nanowires were subjected to strain at several rates, and we concentrated our attention in the specific case of a wire with an atomistic arrangement based on the intercalation of icosahedral motifs forming a Boerdijk-Coxeter (BCB) spiral, and compare it against results of nanowires with fcc structure and (001), (011), and (111) orientations. We found that the BCB nanowire is more resistant to breakage than the fcc nanowires. In the simulations of lateral compression, we made a strain analysis of the trajectories, finding that when a gold decahedral nanowire is compressed by the AFM tip in a direction parallel to a (100) face, the plastic deformation regime is considerably larger than in the case of compression exerted in a direction parallel to a twin plane, where the fracture of the wire comes almost immediately after the elastic range ends. The strain distribution and elastic response in the compression of nanoparticles with different geometries is also discussed. INTRODUCTION The mechanical properties of nanostructures are interesting for several reasons, but the main reason is very concrete and pragmatic: in order to use nanostructured materials as part of nanoelectronic devices, as junctions that act as the connections between interacting active elements, it is desired that these materials have the structural characteristic that gives them a mechanical response that assures stability when the device is exposed to external stress and changes in thermal conditions. A recent study by the group of J. Greer at Caltech is a very complete example of this issue: in this study, Greer et al. fabricated nanometric bars of Nickel and phosphorus, and subjected them to tensile strain; they found that the resistance to fracture of the nanobars depend very critically on the presence of flaws. As they state it very adequately, the size-dependent strength in nanostructures is a well-stablished fact, but there are still many open questions on the specific mechanisms involving stress and fracture in these nanostructures.1 Efforts in this direction can be traced as far as almost twenty years ago, in research developed by the group led by Landman and Whetten, where they explain the o
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