In Situ Studies of Deformation and Fracture in Sputtering Copper Film

Nanocrystalline copper films were prepared by sputtering and then in situ straining experiments were performed using a transmission electron microscope. Macroscopically, these copper films exhibited very low ductility (<l%). Dislocation activity was limited in regions far from propagating cracks. Near stable growing cracks, considerable local plasticity was observed. The evidence of slip activity both within grain interiors and in grain boundaries was also observed. Although some dislocation; moved very fast, others showed rates much lower than those typically measured for bulk copper. Fracture was intergranular, but not brittle. It occurred by linking of microcracks. Microcracks formed within a micrometer or so ahead of the main crack tip, usually within a grain boundary. Linking then took place by the easiest available path.