Strain Relaxation-Induced Twin Interface Migration and Morphology Evolution of Silver Nanoparticles

The twinned structure of nanoscale metal particles is considered to be an important factor in the formation of novel morphologies. Nevertheless, most studies are focused on the growth of nanoparticles with stable twinned structures and little is known about the intrinsic relationship between the morphological evolution and the strain relaxation induced by twin boundary migration. In this study, we elucidated the mechanisms of symmetry breaking induced by strain relaxation in Ag nanoparticles by employing transmission electron microscopy, electron tomography, and strain analysis. The experimental results reveal that decahedral nanoparticles larger than ∼50 nm evolve into asymmetrical rhomboid pyramids to relax the lattice strain energy in the 5-fold twin through twin pole migration. This migration is achieved by coordinating slip and dissociation of partial and perfect dislocations. In addition, we found that the rhomboid pyramid further evolves into a rhomboid bar during growth in a specific way to avoid increasing the strain energy in the crystal.