Self-Seeded Growth of Five-Fold Twinned Copper Nanowires: Mechanistic Study, Characterization, and SERS Applications

A comprehensive mechanistic study conducted on the formation mechanism of five-fold twinned copper nanowires by heating copper (I) chloride with oleylamine at 170 °C is presented. Electron microscopy and UV-visible absorption spectra are used to analyze the growth mechanism of copper nanowires. High-resolution transmission electron microscopy and selected-area electron diffraction are used to investigate the detailed structure of copper nanowires and nanoparticles, and a five-twinned structure is shown to exist in the copper nanowires and nanoparticles. Additionally, experiments have been performed to indirectly confirm that oleylamine preferentially adsorbs on the 100 facets of growing crystals. On the basis of the above results, the self-seeded growth of copper nanowires is confirmed. In the initial stage of reactions, copper nanoparticles with two distinctive sizes are formed. As the reaction proceeds, larger five-twinned copper nanoparticles serve as seeds for anisotropic crystal growth. Further, copper atoms generated from an Ostwald ripening process or reduction reactions of a copper (I) chloride-oleylamine complex continue to deposit and crystallize on the twin boundaries. Once the 110 planes are generated, oleylamine preferentially adsorbs on the newly formed 100 facets and then guides the formation of nanowires. The electrical resistivity of a single copper nanowire is measured to be 41. 25 nΩ-m, which is of the same order of magnitude as the value of bulk copper (16. 78 nΩ-m). Finally, an effective surface-enhanced Raman spectroscopy active substrate made of copper nanowire is used to detect the 4-mercaptobenzoic acid molecules.