Cross-Flow Purification of Nanowires

摘要

Nanoparticles and other low-aspect-ratio shapes are a common byproduct from the solution chemical growth of nanowires. They are formed because nucleatioh is not instantaneous, and growth is diffusion-limited, causing particles to grow along multiple pathways. These unwanted morphologies can bring much difficulty to the subsequent material processing steps and degrade the material performance in device applications. For example, the presence of these short particles greatly affects the assembly of the nanowires. When making two-dimensional (2D) arrays of nanowires, the byproduct particles act as structural defects, disrupting the packing of the nanowires. Even a small number of particles can prevent the formation of a 2D lattice. On the other hand, as many properties of nanoparticles are highly size- and shape-dependent, such byproducts can have a detrimental effect on the quality of the final nanowire material. For example, metal nanowires, made for example of Ag, have rapidly attracted attention as an alternative material to indium tin oxide (ITO) for making flexible transparent conductor thin films. Although there has been great success in the synthesis of Ag nanowires, predominantly by the polyol route, the product is often contaminated by low-aspect-ratio particles and rods. The presence of these nanoparticle impurities in the nanowire network is be highly undesirable because they would only have a marginal contribution to the electrical conductivity as they are too small to provide effective current pathways, but they will cause significant optical loss owing to their stronger light scattering properties. As the commercial production of a silver nanowire transparent conductor has emerged, there is a pressing need for a purification method that can meet the industrial scale of synthesis.