In-situ transmission electron microscopy study of nanotwinned copper under electromigration

Nanotwinned copper has drawn growing attention recently due to its substantially enhanced mechanical strength and negligible increase in electrical resistivity. The stability of nanotwins under mechanical and electrical stressing becomes a critical consideration. Using a high resolution transmission electron microscopy, we observed that the {112} incoherent twin boundary (TB) and {111} coherent TB migrate at a rate of 0.06 ~ 0.09 nm/s in copper under an electric current density of 2×10⁶ A/cm². The TB migration is possibly associated with an atomic step moving along either {111} or {112} plane and the TB migration rate is mainly controlled by the incubation time of forming new atomic steps. To form such atomic steps, EM-induced diffusion at junctions where TBs meet a grain boundary or free surface may play an important role.