Preparation of Ultramicroelectrode Array of Gold Hemispheres on Nanostructured NiAl-Re

Nanopore arrays prepared by partial dissolution of the fibrous phase present in a directionally solidified NiAl-Re eutectic alloy were employed as starting material for the design of arrays of microelectrodes. Polycrystalline gold hemispheres have been grown onto the created nanopores by electrodeposition. The applied pulses resulted in the formation of gold nuclei that grew to fill up the pores. After complete cover of the pores, the application of further pulses resulted in the deposition of more gold particles onto the existing ones, creating microspheres with a diameter of 2-4 µm and evenly distributed on the rhenium pores. Polarization of the sample prior to the gold electrodeposition ensured formation of passive oxides on the matrix of the NiAl-Re samples, thus favoring the selective plating of gold onto the pores only. The resulting arrays of gold microspheres showed a good electrochemical performance when voltammetric analysis of Fe(II)/Fe(III) was carried out, which demonstrates the suitability of the deposits as electrochemical microsensors. A subsequent selective dissolution of the matrix revealed a structure which is in full agreement with the proposed model. Gold hemispheres (2-4 µm diam) reside on top of rhenium nanowires (400 nm diam). These spheres showed a sufficient mechanical stability and adherence to the parallel aligned nanowires.