March 2000

Intelligent Self-Assembly

By David Rotman

One dream of scientists making ultrasmall devices is coaxing materials to spontaneously form structures on a scale of micrometers, even nanometers. (A nanometer is one billionth of a meter.) The problem is how to control the location and orientation of structures made by this "self-assembly." Now a group of researchers at Princeton University may have stumbled across one solution: a way to form precise arrays of tiny pillars exactly where you want them. By providing a potentially cheap and easy method to make tiny structures, the technique could eventually lead to such things as even smaller integrated circuits and a simpler way to sort DNA molecules.

Researchers in the lab of Stephen Chou, professor of electrical engineering, were working on a fabrication method using a mask to imprint nanometer-scale patterns on a polymer film. In a surprising result, they found that when microscopic particles of dust prevented the mask from contacting the polymer, micrometer-sized columns spontaneously formed in neat arrays under the protruding parts of the mask. Chou says he still doesn't know exactly why the pillars form. But he quickly realized it could be a much more controllable method to self-assemble tiny structures.

"The power of the method," says Chou, "is that it puts intelligence in self-assembly, and it could work for almost any [liquid] materials." Chou is working on ways to make organic light-emitting devices used in flat-panel displays in which each pixel consists of a cluster of tiny pillars-a result that would greatly improve the reliability and color reproduction of the displays. Chou also suspects that the ultrasmall pillars could be used to form interconnects in nanoscale electronic devices.