Twinning by Controlled Cluster Coalescence: A Unified Pathway to Single‐Crystalline, Single‐Twinned, and Penta‐Twinned Gold Nanocrystals

The twin structure of metal nanocrystals is essential for engineering their electric conductance, mechanical stress, thermal stability, as well as morphology. Yet the formation pathway of twin planes in a nanocrystal during colloidal synthesis has not been fully established due to the lack of high-yield single-twinned (ST) structures that are thermally stabilized between the single crystalline (SC) and penta-twinned (PT) phases. Here we verify a cluster coalescence mechanism that unifies the high-yield synthesis of SC, ST, and PT gold nanocrystals in solution. ST gold seeds with a yield exceeding 85% can be directly produced by adjusting the cluster coalescence to an intermediate level through the surface potential, density, and size of the clusters. Molecular dynamics simulations and control experiments indicate that the ST seeds are enriched after the coalescence of 2-4 clusters with a size of about 2-5 nm. This general paradigm provides design guidelines for the synthesis of metal nanocrystals with desired twin defects.