Credit: © 2006 Nature Materials

Photolithography is adept at patterning the same feature over large surfaces, whereas chemical etching and metal plating offer a high level of control over feature dimensions on nanometre scales. A hybrid of these techniques is the strategy behind lithographically patterned nanowire electrodepostion, a fabrication method developed by Reginald Penner and co-workers1 at the University of California, Irvine in the USA.

The process begins by making a ‘sandwich’ of a thin nickel layer between a glass substrate and a top layer of photoresist. Thin strips of the photoresist are removed to expose the nickel, which is then ‘over-etched’ to leave behind carved out spaces under the remaining photoresist. Standard electroplating is used to fill this space with gold, platinum or palladium to make thin metal wires.

The thickness and width of the metal wires — both of which can be controlled with 5 nm precision — are determined by the thickness of the nickel layer and the electroplating time. This technique can be used to make wires that are as small as 18 nm thick and 40 nm wide, though the minimum wire separation is limited by the photolithography step.