July 2001

Gold Standard

Nanotech

By Erika Jonietz

As researchers engineer everything from computer chips to drug-discovery tools down to smaller and smaller scales, making these devices is becoming excruciatingly difficult. The principal micromanufacturing technique, photolithography, uses light to etch microscopic features onto a silicon surface; but it's expensive and exacting. One promising alternative is called "soft lithography," a technique that uses flexible rubber stamps to fabricate devices with micro- and nanoscale features.

Until now soft lithography has mainly been used to make tiny devices like microfluidic chambers used for biological research. But Harvard University chemists George Whitesides -soft lithography's pioneer-and Heiko Jacobs have found a new application: transferring nanoscale patterns of electrical charge onto electrically conductive polymers. This advance could mean a cheaper and easier way to manufacture very small data storage and optical devices.

The Harvard scientists accomplished the trick by first building a mold made of silicon, using traditional photolithography methods to carve out the pattern. They then poured rubbery silicone into the mold to make the stamps, which they coated with a thin layer of gold. When the researchers pressed one of these stamps against a polymer film and ran a current through them, the pattern was transferred to the polymer as a series of positive and negative charges. A single mold can churn out multiple stamps, and each can be used repeatedly.

Although the new technique is now just a lab demonstration, potential new applications include encoding data on charge-based storage devices such as "smart cards"-credit-card-sized pieces of plastic used to verify the cardholder's identity-or constructing waveguides for optical telecommunications switches. Says Christopher B. Murray, manager of nanoscale materials and devices at IBM's T. J. Watson Research Center, "This is one more step in a number of beautiful efforts to explore nontraditional patterning technology."