In situ TEM observation of grain annihilation in tricrystalline aluminum films

Capillarity-driven grain boundary (GB) motion in Al tricrystalline thin films has been investigated by in situ transmission electron microscopy at intermediate temperatures. The GBs were observed to move erratically, with alternating periods of motion and stagnation, followed by rapid shrinkage of the grain and eventual annihilation accompanied by the emission of dislocations. The absence of measured deformation and grain rotation during the GB motion suggests that it is not associated with shear-migration coupling. This is in contrast to observations on the stress-driven motion of planar GBs. The present results can be interpreted by the absence of deformation associated with low internal applied stress or alternatively by a low shear-migration coupling factor. In both cases, a large amount of atomic shuffling is needed to account for the migration of grain boundaries.