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

TL;DR

This study reveals that in fcc metals, grain boundaries with shifted tilt axes near surfaces are energetically preferred, driven by the elimination of high-energy boundary core facets, impacting properties like electromigration.

Contribution

The paper demonstrates that low energy core-shifted grain boundaries are favored across multiple fcc metals, extending findings beyond copper.

Findings

Core-shifted boundaries are lower in energy in Cu, Al, Ni, Au, and Pt.

Energy reduction correlates with elimination of boundary core facets.

Implications for electromigration and metal surface properties.

Abstract

Grain boundaries with [111] tilt axes are common in polycrystalline face centered cubic metals. For copper (111) films, emergent grain boundaries close to 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.