PNNL

Abstract

The occurrence of 5-fold twinned nanoparticles, commonly observed in both natural and synthetic crystalline materials, leads to unique properties. However, nearly 200 years after their discovery, the formation mechanism is still ambiguous. Using in situ high-resolution transmission electron microscopy combined with molecular dynamics simulations, we demonstrate that 5-fold twinning occurs via repeated oriented attachment of ~3 nm gold, platinum, and palladium nanoparticles. These attachment events create regions of negative curvature and high-energy grain boundaries, which then accumulate strain as surface diffusion and other atomic rearrangements eliminate the curvature. To relieve the strain, the boundaries decompose via nucleation and growth of a special class of twins whose net strain is zero. The results provide a quantitative understanding of the 5-fold twinning process; this knowledge provides guidance for interpreting and controlling twin structures and morphologies of a wide range of materials, including metals and oxides.