Nucleation, growth, and dissolution of silver nanostructures formed in nanotubular J-aggregates of amphiphilic cyanine dyes.

Solution fabricated high aspect ratio silver nanowires are of interest because of their usability in plasmonic devices or transparent electrodes. Recently, silver nanowires with diameters of 6.5 nm and lengths exceeding tens or hundreds of microns were grown by reduction of silver ions within the inner volume of nanotubular J-aggregates of an amphiphilic cyanine dye. Unlike in other soft template systems, the anisotropic growth of the silver wires is not caused by different screening of the diverse facets of silver crystals. Instead, the shape of the wires replicates the inner space of the tubes without destroying the template. This effect is demonstrated by ex-situ observation of the growth of the silver wires via transmission electron microscopy. The wire growth is initiated by exposure to blue light and starts with small, isolated crystallites within the tubular aggregates. The crystallites grow into pieces of wires that finally coalesce into continuous wires. The growth is mediated by material transport through the membrane-like wall of the dye aggregates. This wall permeability is further demonstrated by dissolution of the silver wires via oxidative etching by addition of sodium chloride. It is concluded that the cyanine double layer wall is permeable for ions such as silver, sodium, chlorine, and water molecules. This permeability permits control of the wire length through the concentration of chlorine when oxygen is removed from the solvent.