Kinetics of Fivefold-Twinned Nanowire Growth in Colloidal Syntheses

Kristen Fichthorn and Xi Qi

There has been significant emphasis recently on the synthesis of fivefold-twinned Ag and Cu nanowires, which are considered to be excellent candidates for transparent conductors in flexible and stretchable electronic devices. A fundamental understanding of nanowire growth is important in achieving optimal syntheses. Nanowires grow from fivefold-twinned seeds, which are likely Marks decahedra, with {111} end facets, {100} side facets, and small {111} notches at the corners of the pentagonal cross-section. High-resolution transmission electron microscopy studies have shown that the {100} side facets can achieve a stepped structure, that runs parallel to the nanowire axis and is likely associated with the relief of strain in these structures. Our climbing-image nudged-elastic band method calculations of diffusion barriers based on embedded-atom method potentials indicate that diffusion in the {111} notches and along step edges is significantly faster than diffusion on {100} facets. Thus, these structures become “superhighways” that channel atom diffusion to the wire ends to increase wire aspect ratios. We find that capping agents facilitate all types of diffusion, but especially that along edge notches. We use finite Markov chains to model nanowire growth and to predict net atom fluxes from nanowire “sides” to the “ends”. These simulations can predict anisotropic nanowires similar to those seen experimentally.

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