"Very few methods exist that accommodate the fabrication of complex 3D structures with nanometre-sized structural elements in single machining steps," Andy Trimmer of the University of Virginia told nanotechweb.org. "In principle, any material that is electrochemically active is a candidate for the electrochemical machining method."

Trimmer and colleagues used tungsten tools to create patterns on the nickel substrate. They positioned the tungsten tool near the substrate in an aqueous hydrochloric-acid electrolyte and applied a voltage between the two. The resulting current flow and anodic reaction at the substrate caused regions of the substrate to be machined away. Using ultrashort voltage pulses (about 2 ns long) considerably improved the resolution of the technique.

The scientists used two tools, one a representation of the Rotunda in the grounds of the University of Virginia and the second a 2 x 2 array of cubes. They made these tools by focused ion-beam milling. The electrochemical machining time taken to create the Rotunda pattern to a depth of 400 nm was 1 min 45 s.

According to Trimmer, electrochemical machining combines the advantages of high-resolution features with parallel machining steps analogous to lithography. "We would like to scale the process such that line widths of 30 nm are produced, making electrochemical machining competitive with high-end lithographic processes," he added. "Additionally, we would like to expand the number of materials that we have a recipe for machining."

The researchers reported their work in Applied Physics Letters.