Real-Time Visualization of Diffusion-Controlled Nanowire Growth in Solution

This Letter shows that copper nanowires grow through the diffusion-controlled reduction of dihydroxycopper­(I), Cu­(OH)₂^–. A combination of potentiostatic coulometry, UV–visible spectroscopy, and thermodynamic calculations was used to determine the species adding to growing Cu nanowires is Cu­(OH)₂^–. Cyclic voltammetry was then used to measure the diffusion coefficient of Cu­(OH)₂^– in the reaction solution. Given the diameter of a Cu nanowire and the diffusion coefficient of Cu­(OH)₂^–, we calculated the dependence of the diffusion-limited growth rate on the concentration of copper ions to be 26 nm s^–1 mM^–1. Independent measurements of the nanowire growth rate with dark-field optical microscopy yielded 24 nm s^–1 mM^–1 for the growth rate dependence on the concentration of copper. Dependence of the nanowire growth rate on temperature yielded a low activation energy of 11.5 kJ mol^–1, consistent with diffusion-limited growth