Universal preference for low-energy core-shifted grain boundaries at the surfaces of fcc metals

Grain boundaries (GBs) with [111] tilt axes are common in polycrystalline face-centered cubic (fcc) metals. For copper (111) films, emergent GBs close to the surface have tilt axes that are shifted away from [111] that are lower in energy than the corresponding truncated bulk boundaries. Geometrical analysis and atomic calculations were used to study the driving force for this same relaxation phenomenon in representative fcc elemental metals. We show that the reduction in boundary energy scales with the elimination of energetically costly boundary core facets. We find that, for a wide range of misorientation angles, low-energy core-shifted boundaries are also favored in Al, Ni, Au, and Pt and discuss the significance for electromigration and other metal properties.