Nanowire Synthesis

This research demonstrates how gold nanowires can be successfully synthesized using a dialdehyde reducing agent (polyglutaraldehyde) as a template, onto which a metal (gold) precursor is attached. The synthesis process involves two steps, a seeding and metallization step. During the seeding step, a gold precursor salt (chloroauric acid) is added into a solution of aqueous glutaraldehyde and DMAP (4-Dimethylaminopyridine). Once the temperature and pH of the mixture is elevated, two reactions occur simultaneously – polymerization of glutaraldehyde (which is accelerated by the high temperature and pH used) and gold seeding. In particular, the polyglutaraldehyde formed will act as a reducing agent to break down the gold precursor salt into smaller sized “seeds”. DMAP is added to increase the solution pH (hence accelerating the reactions) and to minimize agglomeration of the Au seeds (facilitating the attachment of Au seeds to the polymer template rather than to one another). The second, or metallization, step involves addition of the synthesized seeds into a CTAB growth solution to form more continuous gold nanowire structures. Particularly, the growth solution allows additional gold to be deposited on the seeds formed. Additionally, by modifying various process conditions, such as the temperature, concentration and composition of growth solution, the length, diameter, and morphology of the nanowires can be altered. Specifically, an increase in gold seeding time increases the length of the nanowires, increasing the concentration of chloroauric acid increases the diameter of the wires and removing silver nitrate from the growth solution changes the shape of the wires. Finally, the study shows how the synthesized gold nanowires can be utilized in plasmonic applications via self-assembly methods that fabricate and pattern thin gold films.