Surface stress driven reorientation of gold nanowires

Atomistic simulations with modified embedded atom method (MEAM), embedded atom method (EAM) and surface embedded atom method (SEAM) potentials reveal that, at certain sizes, a face centered cubic (fcc) gold $⟨100⟩$ nanowire reorients into an fcc $⟨110⟩$ nanowire. In MEAM simulations, the reorientation consists of two successive processes. First, surface stress and thermal vibrations cause the fcc $⟨100⟩$ nanowire to transform into a body centered tetragonal (bct) nanowire. Second, the bct nanowire becomes unstable with respect to shear and transforms into an fcc $⟨110⟩$ nanowire. In EAM and SEAM simulations a different reorientation mechanism exists. The surface stress in the fcc $⟨100⟩$ nanowire induces slip on a $\left\{111\right\}⟨112⟩$ system. Progressive slip on adjacent $\left\{111\right\}$ planes changes the stacking sequence of these $\left\{111\right\}$ planes from ABCABC to ACBACB, and the nanowire reorients into an fcc $⟨110⟩$ nanowire. The difference in reorientation mechanisms is rooted in the differences in the unstable stacking fault energy and orientation dependence of electron density in the potentials. In spite of these differences, the final structures of the reoriented nanowires are the same, which helps to explain why uniform fcc $⟨110⟩$ nanowires are observed much more often in experiments than nanowires of other orientations.