Isotropic Iodide Adsorption Causes Anisotropic Growth of Copper Microplates

Abstract

Control over the shape of a metal nanostructure grants control over its properties, but the processes that cause solution-phase anisotropic growth of metal nanostructures are not fully understood. This article shows why the addition of a small amount (75–100 μM) of iodide ions to a Cu nanowire synthesis results in the formation of Cu microplates. Microplates are 100 nm thick and micronwide crystals that are thought to grow through atomic addition to {100} facets on their sides instead of the {111} facets on their top and bottom surfaces. Single-crystal electrochemical measurements show that the addition of iodide ions decreased the rate of Cu addition to Cu(111) by 8.2 times due to the replacement of adsorbed chloride by iodide. At the same time, the addition of iodide ions increased the rate of Cu addition to Cu(100) by 4.0 times due to the replacement of a hexadecylamine (HDA) self-assembled monolayer with the adsorbed iodide. The activation of {100} facets and passivation of {111} facets with increasing iodide ion concentration correlated with an increasing yield of microplates. Ab initio thermodynamics calculations show that, under the experimental conditions, a minority of iodide ions replaces an overwhelming majority of chloride and HDA on both Cu(100) and Cu(111). While Cu nanowire formation is predicted (and observed) in solutions containing chloride and HDA, the calculations indicate that a strong thermodynamic driving force occurs for {111} facet (and microplate) growth when a small amount of iodide is present, consistent with the experiment.

The Roles of Citrate and Defects in the Anisotropic Growth of Ag Nanostructures

“…Previous studies of anisotropic growth of pentagonally twinned gold nanorods, copper nanowires, and copper microplates with single-crystal electrodes have also reported that the extent of anisotropic growth of the nanocrystal with planar defects is more than 10 times larger than can be accounted for from the ratios of the currents measured on (100) and (111) single-crystal electrodes. − The difference in the extent of anisotropic growth observed for nanocrystals with planar defects and from measurements with single-crystal electrodes may be due to a similar effect as that observed in this work, i.e., that planar defects catalyze atomic deposition. Additional comparisons of the anisotropic growth of single-crystal seeds and seeds with planar defects under identical conditions, with accompanying single-crystal electrode measurements, may shed light on the extent to which planar defects catalyze atomic deposition for gold, copper, and palladium nanocrystals.…”

“…However, one can measure the current density ( j mp ) for either half-reaction at the mixed potential to determine the overall reaction rate. For spontaneous electrochemical reactions that are relatively slow, the j mp can be extracted from a Tafel plot of (log| j | vs E) obtained from the mixed reaction solution. − The seed-mediated growth studied in this paper occurred too quickly for electrochemical analysis of the mixed reaction solution (the reaction is complete in 13 min), so we analyzed the two half-cell reactions separately. We compared reaction rates on Ag(100) and Ag(111) surfaces to measure how citrate affects the facet selectivity of the half-reactions.…”

“…Hexadecylamine (HDA) was found to passivate both Cu(100) and Cu(111) surfaces equally, but adding chloride selectively displaced HDA from the {111} facets on the ends of nanowires, enabling anisotropic growth . Addition of small concentrations of iodide to an HDA-mediated copper nanowire synthesis resulted in isotropic adsorption of iodide on both Cu(100) and Cu(111) but anisotropic growth of Cu microplates . For the case of gold nanorods, bromide exhibited a facet-selective passivation of {100} facets, but cetyltrimethylammonium did not …”

“…66 Addition of small concentrations of iodide to an HDA-mediated copper nanowire synthesis resulted in isotropic adsorption of iodide on both Cu(100) and Cu(111) but anisotropic growth of Cu microplates. 67 For the case of gold nanorods, bromide exhibited a facet-selective passivation of {100} facets, but cetyltrimethylammonium did not. 68 Here we apply single-crystal electrochemistry to quantify how citrate affects the rate of atomic addition to the {111} and {100} facets of silver.…”

Solution-Phase Growth of Cu Nanowires with Aspect Ratios Greater Than 1000: Multiscale Theory

“…If facet-selective deposition cannot completely explain the growth of Cu nanowires with adsorbed Cl and HDA, we considered that surface diffusion could play a role. Our recent DFT study showed that Cl adsorption can reduce the surface energy of Cu(100), relative to Cu(111), and provide a thermodynamic driving force for the growth of {100}-faceted Cu nanostructures, such as nanowires. − Herein, we show how this thermodynamic driving force is manifested kinetically, in faster Cu-atom surface diffusion on Cl-covered Cu(100) than on Cl-covered Cu(111). Below, we show how surface diffusion could play a key role in the growth of Cu nanowires.…”