Atomistic simulations of surface cross-slip nucleation in face-centered cubic nickel and copper

In this manuscript, embedded atom potentials are used to determine the various core structures of glide screw-character dislocations intersecting free surfaces at right and inclined angles in face-centered cubic Ni and Cu. It is shown that the negative constriction forms at free surfaces under certain conditions. The role of various factors affecting the formation of negative constriction at the free surface, negative constriction energy, ledge annihilation and screw dislocation rotation due to Lothe's forces are discussed. The activation energy for surface cross-slip nucleation when the screw dislocation intersects the free surfaces at right angles, in the absence of ledge annihilation forces, is shown to be 0.05 eV in Ni and 0.09 eV in Cu. The activation-energy values obtained via the nudged elastic band method are significantly lower than the activation energy for cross-slip at attractive forest dislocation intersections in these materials. The present results are expected to be useful in understanding the mechanical behavior of micron-sized pillars under pure tension and compression.