Fabrication of rhenium nanowires by selective etching of eutectic alloys

Rhenium nanowires have been fabricated via directional solidification and selective etching of a eutectic alloy. A NiAl-1.5 at.%Re eutectic alloy was directionally solidified using a constant growth rate and temperature gradient, in the Bridgman-type directional solidification furnace. The selective dissolution of the NiAl matrix was achieved with a mixture of HCl:H2O2, and produced an anisotropic etching of the eutectic, with the favoured etching directions aligned in parallel. The corroded surface was dominated by long rhenium fibres (diameter ~400 nm), although shorter, and sometimes more rectangular wires were also observed in some sections. Digestion of the NiAl-Re eutectic in sulphuric acid, on the other hand, produced mainly long rhenium fibres of consistent shape and length. Both etching procedures might subsequently be applied for the preparation of nanodisc electrode arrays by embedding the obtained Re nanowires into a polymer and grinding until the wires are exposed. The reduction on the electrode area inherent in the use of such nanoelectrodes would allow a considerable increase in the signal-to-noise ratio, thus favouring the system for its application in analytical sensors. The use of rhenium in the electrode formation might also favour its application in high-temperature measurements.