Atomistic simulation of the deformation of gold nanopillars

We perform a series of molecular dynamics simulations of the uniaxial compression of cylindrical gold nanopillars. Yield occurs via Shockley partial dislocation nucleation at the surface. Dislocation nucleation is preceded, in some cases (depending on the interatomic potential), by an elastic instability of the nanopillars, either Euler buckling or shears folding. For some potentials, this buckling is related to compressive stress-driven face-centered cubic-hexagonal close-packed phase transitions in the bulk. In cases in which dislocation nucleation is not preceded by an elastic instability (this depends on the choice of the interatomic potential and loading direction), the yield stress is found to be either a parabolic (i.e. described by the relationship A - B T with A, B = const) or linear function of temperature, T. We suggest that Shockley partial dislocation nucleation at the surface of the nanopillar occurs at a critical strain, where the local strain has contributions from the homogeneous elastic strain and an atomic-level thermal strain (associated with the thermal vibrations). This model explains the observed temperature dependence of the yield stress of the compressed nanopillars.