Noble and coinage metal nanowires by electrochemical step edge decoration

A general method is described for the electrodeposition of long (>500 mum) nanowires composed of noble or coinage metals including nickel, copper, silver, and gold. Nanowires of these metals, with diameters in the range from 60 to 750 nm, were obtained by electrochemical step edge decoration (ESED), the selective electrodeposition of metal at step edges. Nanowire growth by ESED was accomplished on highly oriented pyrolytic graphite surfaces by applying three voltage pulses in succession: An oxidizing "activation" pulse, a large amplitude, reducing "nucleation" pulse, and a small amplitude reducing "growth" pulse. The activation pulse potential was optimized to oxidize step edges on the graphite surface just prior to deposition. The nucleation pulse had an overpotential for metal deposition of between -150 and -500 mV and a duration of 5-100 ms. The growth pulse had a small deposition overpotential of less than -100 mV. Nanowire growth was characterized by a time-independent deposition current, and consequently, the nanowire radius was proportional to the square root of the deposition time in accordance with the expected growth law.