Parallel 'nano-soldering' technique chosen for year's top-50 by Nanotech Briefs

You should have so much patience to solder nanowires to nanoelectrodes. Talk about fine work. (A nanometer is a billionth of a meter.)

That's why a new electroplating process that simultaneously joins many silicon nanowires to many prepatterned electrodes was selected for a 2008 Nano 50 Award by Nanotech Briefs.

The process removes many difficulties.

"All of the electroplating is done in parallel," says Sean Hearne, a Sandia National Laboratories researcher at the Center for Integrated Technologies (CINT). "Everywhere there's a metal contact, the electroplated nickel grows over the nanowire, capturing it."

CINT is a DOE Office of Science nanotechnology center led by Sandia and Los Alamos National Laboratory.

Previous methods connected electrodes to nanowires one contact at a time. That kind of service may sound great in stockbroker ads; in a lab, it's merely tedious.

Other methods required complex processes that included masking, metal deposition, and stripping, which often damaged the nano-wires.

The process could be important for commercial applications of semiconducting nanowires used in electronic sensor arrays, because it allows for the parallel processing of millions of nano-wires on a single wafer at lower cost than previous lithographic techniques.

In the team's approach, microarrays of composite gold electrodes were lithographically formed on oxidized silicon substrates, followed by electric-field-assisted alignment of silicon nanowires between the electrodes.

The nanowire ends were then embedded in nickel by selective electrodeposition over the prepatterned electrodes. Annealing to 300 °C provided good electrical contacts for the doped nanowires.

The approach provides a parallel, maskless method to establish metal contacts to nanowires without need of high-resolution electron beam lithography for electrical and mechanical applications.