We have discovered two methods for the electrodepositing long (> 500 µm), nanowires composed of noble or coinage metals including nickel, copper, silver, and gold (see Figure below). This paper focuses on the "MultiPulse Method" shown at right. Noble metal nanowires with diameters in the range from 60 nm 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 -200 and -500 mV and a duration of 5-10 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.

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 -200 and -500 mV and a duration of 5-10 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.

Figure 2. Nanowire diameter versus (deposition time)^1/2 for the growth of nanowires composed of four metals as indicated. Each series of experiments for a particular metal were performed using a single graphite crystal in order to limit the variation in the step edge density from experiment to experiment. This crystal was cleaved before each experiment to expose a fresh, clean graphite surface. Error bars for each data point are twice the standard deviation for the mean particle diameter.