(552a) Chloride and Hexadecylamine Promote the Solution-Phase Growth of Copper Nanowires

Fivefold-twinned Cu nanowires have promising applications in flexible electronics. These nanowires can be prepared using solution-phase synthesis, which typically involves metal salt precursors, reducing agents, and capping agents. Although there have been numerous observations of Cu nanowire growth in colloidal synthesis, the detailed mechanism remains elusive.

It has been proposed that the anisotropic growth of Cu nanowires is due to the preferential binding of the capping agent, hexadecylamine (HDA), to the {100} “sides” of the nanowires, but there is no direct experimental evidence to support this hypothesis. In addition, molecular-dynamics simulations indicate that HDA alone is unlikely to promote nanowire growth. Experimental studies show that the adsorption of Cl^- on the nanowire surfaces may influence the binding of capping agent HDA in a facet-selective way. Here we investigate the cooperative role of chloride ions and HDA in promoting anisotropic nanocrystal growth, by studying their co-adsorption on Cu surfaces using first-principles, dispersion-corrected, density functional theory (DFT).

DFT results show that both Cu(100) and Cu(111) are passivated by a HDA adlayer at low concentrations of Cl, while repulsive electrostatic interactions between adsorbed Cland HDA lead to the desorption of the HDA layer at higher concentrations of Cl. Desorption of the HDA layer occurs at a lower Cl coverage on Cu(111) than on Cu(100). Thus, free Cu atoms and other growth species can add to the open {111} facets, leading to the anisotropic growth, in agreement with synthetic results, as well as electrochemical results from single crystals of Cu.