Solution synthesis of helical gold nanowire bundles†
Helical nanostructures are important nanoscale building blocks. While only a few methods are available for synthesizing helical metal nanostructures, those involving collective twisting behaviour are even fewer. Here, we report a solution synthesis of Au nanowire bundles with hierarchical helical constructions. Ultrathin nanowires with diameters of only about 10 nm formed huge ribbon bundles that have a width of 0.5–1 μm and thickness of a few hundreds of nanometres. These bundles extended to hundreds of micrometres and curled into helices. Mechanism studies revealed that the white floccules formed by Au(I) and a thiol ligand are of critical importance for both the nanowire growth and helical bundle formation. The nanowire growth took place in the floccules following the previously reported active surface growth mode, and the bundle formation was due to the splitting of the active surface. Most importantly, the floccules assisted the strain-induced curling process that yielded helices. As the length of the bundles keeps increasing and they break out from the surrounding floccules, they would have to pass through the pores of the floccules. The imbalanced squeezing at the pore caused the bundles to curl into helices.