Atomistic simulations of dipole tilt wall stability in thin films

In this work, we use molecular statics to study the stability of a pair of symmetric dipole tilt walls in Cu thin films. Two geometric wall parameters, the dislocation spacing and wall separation distance, are varied in the calculations. We find that even closely spaced dipole walls can be stabilized in a thin film under no applied strain, and with this insight, develop a stability map that identifies the regime of maximum dislocation spacing and minimum wall separation for which dipole walls can reside in the film. In addition, we show that a critical in-plane tensile strain exists that can destabilize the dipole walls and transition the film to a wall-free state. The simulations reveal that the wall recovery process occurs by sequentially annihilating alternating pairs of dipole dislocations rather than sudden, simultaneous annihilation of an entire wall. Dipole wall stability is rationalized based on a substantial enhancement in the Peierls barrier of the wall dislocations due to the reorientation of the lattice between the walls and narrowing of their intrinsic stacking faults, two effects that have atomic-scale origins.