NANOWRITING Width of polythiophene lines is around 50 nm.

The team used a direct-writing technique known as electrochemical dip-pen nanolithography to prepare well-defined polythiophene lines with widths of less than 100 nm on oxidized silicon wafer surfaces.

The work was carried out by assistant professors Jie Liu and Mark W. Grinstaff and graduate students Benjamin W. Maynor and Shaun Filocamo (J. Am. Chem. Soc., published Dec. 19, 2001, ASAP, http://pubs.acs.org/journals/jacsat).

The polymer lines are prepared by coating an atomic force microscope tip with 3,4-ethylenedioxythiophene (EDOT) and then translating the tip across the silicon wafer. The monomer is electrochemically polymerized at the interface by applying a voltage between the tip and the wafer. The morphology of the nanowires is controlled by varying the humidity, applied voltage, and tip translation speed.

Poly-EDOT is a well-known conducting polymer that has already attracted considerable commercial interest for use as antistatic, electrostatic, and conducting coatings, as well as for light-emitting diodes.

"The capability to direct-write and pattern polymeric materials with interesting electronic and electro-optical properties at the nanoscale creates a number of opportunities since a large variety of monomers/polymers are available," the authors suggest. They note that current techniques--such as photolithography, microcontact printing, template synthesis, and scanning electro- chemical microlithography--possess significant limitations for patterning conducting polymers in the sub-100-nm regime.

"Their big contribution is to get the technique to work for conducting polymers," explains Chad A. Mirkin, a chemistry professor at Northwestern University. "It is a major step forward to making nanocircuitry out of these types of materials."

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