Controlled Growth of Highly Aligned Cu Nanowires by Pulse Electrodeposition in Nanoporous Alumina

Metallic nanowire networks are emerging as potential replacements for transparent conducting oxide coatings because of their high conductivity, flexibility and relative transparency. However, a cheap, reliable and controlled manufacturing process is required to exploit this and the surface of the copper nanowire needs to be protected if high conductivity is to be retained. In this study a fabrication method for highly aligned and densely packed copper nanowires with controlled length using pulse-electrodeposition and a nanoporous alumina template has been developed. Nanoporous alumina was obtained by anodisation of pure aluminum in oxalic acid using a two-step anodisation process. In order to provide the conductivity at the bottom of the pores, a dendritic structure at the interface was created through the stepwise voltage reduction method with a voltage reduction rate of 15 V/s followed by mild chemical etching. Highly repeatable near 100% filling of copper is achieved. Copper nanowire length was highly controllable from 100 nm to 2 μm with a fixed diameter of 60 ± 5 nm by monitoring current density during the deposition. Such controlled growth of Cu nanowires could lead towards transparent conducting layer applications but the protection of the material against oxidation remains an issue.