Copper nanowires and silver micropit arrays from the electrochemical treatment of a directionally solidified silver–copper eutectic

The method of fabricating metallic nanowires from directionally solidified eutectics was applied to the silver–copper system. The silver–copper alloy, 39.9 at.% copper, was directionally solidified in a Bridgman-type oven held at 850 °C. SEM imaging revealed a mixed fibrous and lamellar microstructure. The fastest solidification rates produced fibres and lamellae with widths as small as 300 nm. Electrochemical conditions for the selective dissolution of silver and of copper were determined from the combined Pourbaix diagram for silver and copper and applied to the directionally solidified alloy. Subsequent microscopic investigations yielded copper nanowires with diameters in the 300–640 nm range and hexagonal arrays of micropits in the silver matrix with diameters of 1 μm. The chosen volume fraction of the Ag–Cu system is the only one that matches exactly the theoretical value of π−1 which separates fibrous from lamellar structures. It is demonstrated that the simultaneous formation of fibres and lamellae in the same sample occurs for this unique borderline system.