Halides have played a significant role in achieving shape control of metal nanocrystals, but the exact mechanisms are not well understood. In this work, we focus on shape control of Cu nanowires and nanoplates.   We used quantum density-functional theory (DFT) calculations to show that 1/3 and 1/2 monolayer (ML) coverage of Cl on Cu(111) and 1/2 ML of Cl on Cu(100) are the configurations with the lowest surface energies as a function of the solution-phase concentration (chemical potential) of chloride, consistent with experiment.  When the Cu surfaces contain adsorbed chloride, the surface energy of Cl-Cu(111) is higher than Cl-Cu(100) and a stronger binding of Cu adatoms on Cl-Cu(111) is observed.  This is the opposite trend to what occurs on the bare Cu surfaces.  We also find that absorbed Cl facilitates the diffusion of Cu adatoms on Cu(100) by decreasing the diffusion-energy barrier from 0.55 eV on bare Cu(100) to 0.15 eV on 0.5 ML Cl-Cu(100), but hinders the diffusion on Cu(111) by increasing the barrier from 0.04 eV on the bare surface to 0.23 eV on the Cl-covered surface. Furthermore, the {100}-{111} interfacet barrier favors transport from Cu(100) to Cu(111).  All of these factors promote the growth of Cu into nanowires with long {100} side facets and {111} end facets.  A model based on the theory of absorbing Markov chains indicates that nanowires with high aspect ratios, comparable to those in experiment, are predicted based on values of DFT-predicted surface diffusion coefficients.

Kinetics of halide-mediated Cu nanowire growth

ACS Spring Meeting 2021

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