Observations of dislocation motion and stress inhomogeneities in a thin copper film

In situ transmission electron microscopy has been utilized to study dislocation plasticity in a 200 nm thick copper film. The behavior of dislocations in a [111]-oriented grain was recorded during a thermal cycle. During cooling, it was observed that dislocations were emitted from a grain boundary triple junction in regular intervals of 30°C to 40°C. Subsequent glide occurred on a (111) plane parallel to the film surface, despite the expectation of zero resolved shear stress on such planes. The initial emitted dislocations remained close to the triple junction, avoiding contact with another [111] grain rotated by 17°. Glide into the opposite end of the grain was initiated only after the injection of several additional dislocations, which induced strong curvature in all dislocations near the active triple junction. Post mortem examination of dislocation curvature revealed that an inhomogeneous stress state existed within the grain.