Getting Nanowires into Correct Position Could Lead to Industrial Scaling

There have been a number of methods developed for growing nanowires. The problem for electronics applications has been attaching nanowires to components and once attached getting them organized into a two-dimensional array.

A solution to the first problem has been to use nanowires both for the components and the interconnections.

But the second problem has been a little trickier--getting them in the right position. Fluid flow has been experimented with, where the nanowires fall into parallel orientations just like logs in a river.

Later, researchers exploited this phenomenon by employing the Langmuir-Blodgett

Technique. Basically, the nanowires were collected in large groups on the surface of water and then transferred to a substrate.

Researchers at the National Institute of Standards and Technology's (NIST) Surface and Interafce Research Group, led by Dr. Babak Nikoobakht, have taken a different approach. They have grown the nanowires directly onto the substrate, and done it so they are aligned horizontally to the substrate rather than perpendicularly.

A schematic of the photolithography process for scalable fabrication of nanowire devices can be seen below. (a) Gold pads and fiducial marks are deposited on the surface. (b) NWs are grown selectively from the two sides of the gold pads. (c) Metal electrodes and bonding pads are placed exactly on NWs by alignment of fiducial marks.

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By growing the nanowires directly on the substrate, multiple steps are eliminated that are needed in the other methods to get the nanowires in the correct orientation on the substrate.

As Nikoobakht relates in a recent interview , "Our method has a minimum number of steps. It combines a chemical growth method with well known optical lithography techniques. Nanowires are grown where they need to be."

The devices created in the lab can work as Field-Effect Transistors (FETs), but Nikoobakht concedes that it could take years to establish their performance and stability.

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