HANCOCK, N.H. Researchers at the California Nanosystems Institute have devised a precise way to create nanowire arrays using a standard semiconductor process-molecular beam epitaxy-to make the metal wires.
The approach, called superlattice nanowire pattern transfer (Snap), requires no photolithography or such exotic techniques as nanoimprint technology, the researchers said.
Molecular beam epitaxy is able to lay down semiconductor materials one atomic layer at a time, creating precise structures. The Snap process begins with a standard gallium-arsenide/aluminum-gallium-arsenide superlattice, grown by molecular beam epitaxy, that forms an alternating sequence of layers of each type of material. A selective-etch process is then applied that removes some of the aluminum-gallium-arsenide, creating a gallium-arsenide template pattern for defining the nanowires.
The template is tilted at an angle, and metal is deposited so that the top of each gallium-arsenide rib is coated and the metal wraps around one edge of the rib. The metallized template is then pressed onto a layer of epoxy on a substrate, and the gallium arsenide is etched away, leaving an array of wires.
The research group was able to create platinum nanowires as small as 8 nanometers wide, spaced 16 nanometers apart. The biggest challenge in using the wire arrays will be finding some process for building contact structures. The wire arrays are far smaller than the resolution obtainable with electron-beam lithography, so integrating them into semiconductor processes will be difficult.
The advantage of the process is the regularity of the wire pattern. Regularity has proved difficult to achieve in other nanowire projects. But it is an important step toward manufacturable nano-wire-based systems because it would enable the creation of standard contacts to the wires, the researchers noted in a paper published in the April 4 issue of Science.
The nanowire arrays can also be used as a template to create wire arrays from semiconductor materials.
The researchers also built nanowire arrays over an air gap to create nanoscale mechanical resonators that had a frequency of 162.5 MHz.