Invited
DEFORMATION OF BI-CRYSTALLINE TWINNED GOLD NANOWIRES

The basic mechanisms for nanoscale deformation of bi-crystalline twinned Au nanowires, containing a longitudinal twin boundary, are investigated. A combined experimental-computational study, including in-situ transmission electron microscopy (TEM), in-situ scanning electron microscopy (SEM) and molecular dynamics (MD) simulations, is performed. The pre-existing twin boundary was found to alter the strength and ductility of the nanowire. Experimentally, deformation twinning was observed in both bi-crystalline and pristine (without pre-existing twin boundaries) nanowires. However, the twinned regions in the bi-crystalline nanowires are found to be thinner than in the pristine ones. MD simulations shed light on the underlying dislocation mechanisms. The onset-of-plasticity was found to be controlled in both types of nanowires by the nucleation of dislocations at the edges of the nanowire. However, while in pristine nanowires consecutive nucleation events and the lack of pre-existing obstacles for dislocation motion formed twins easily, the nucleated dislocations in the bi-crystalline nanowires interact with the longitudinal twin boundary. We discuss the different dislocation-twin boundary interactions and we show that a coordinated deformation twinning is required to detwin the longitudinal twin and to form twins along the nanowire (see Figure). This mechanism limits the extent of the twinned regions. Additionally, the twinned regions in both types of nanowires deform plastically via ordinary dislocation plasticity, eventually leading to fracture in the twin. We conclude that the ductility of the bi-crystalline nanowires is controlled by the extent to which the nanowire can deform via deformation twinning.