Electrodeposition of gold on tungsten nanowires present in NiAl-W eutectics
Sprache des Titels:
The formation of gold nanoelectrode arrays was investigated by electrodeposition of the metal on the tungsten nanowires present in directionally solidified NiAl-W eutectics. The tungsten fibres present in the eutectic were conditioned prior to the electrodeposition, and the NiAl matrix was simultaneously passivated by formation of Al2O3 oxide. The simultaneous oxidation of W to W(VI) species for the formation of nanopores, and growth of passive Al2O3 oxides on the NiAl matrix was studied for different polarisation potentials. Anodisation of the samples at potentials <0.7 V resulted in the formation of thin oxide films, and therefore the NiAl matrix remained partially active. In order for the matrix to be fully passive, and the fibres to dissolve and form nanopores, the initial polarisation must be run at 0.7 V vs. SHE. The electrodeposition of gold on the conditioned samples was afterwards optimised for the filling of the pores. When the deposition was run by application of reverse current pulses the obtained gold structures presented a hemispherical shape with a radius that increased with the duration of the cathodic pulse. The electrodeposition of gold from more diluted Au(I) solutions under potentiostatic conditions yielded the formation of thin Au deposits in the nanopores. The nucleation and growth mechanisms involved in the process were determined from the potentiostatic current transients in all the examined cases. It was found that instantaneous nucleation took place for the more concentrated solutions, whereas mixed processes were observed for diluted amounts of Au(I).