Behind the mask

It could be the most unexpected display of patterns since crop circles - the self-assembly of a minute array of pillars in a sheet of plastic resin. A duo of Princeton researchers made the discovery while investigating nanoimprint lithography, a new patterning technology for hard disks. The researchers say the ultrasmall plastic structures could result in new computer memory chips, improved flat-panel displays, even devices to sort DNA molecules. Stephen Chou, a professor of electrical engineering, and his graduate student Larry Zhuang were pressing a mask into soft plastic polymer when dust prevented the two pieces from coming together. Instead of imprinting, the procedure resulted in a minute, perfectly ordered array of pillars rising up toward the mask. Each pillar is about a half a micron in height and width. Chou calls the production technique Lithographically Induced Self Assembly, or LISA.

The results of his discovery appear in the December issue of the Journal of Vacuum Science and Technology. LISA eliminates the need for a carefully engineered mask as the mask merely defines the outline of the array of pillars. Chou predicts the technique will work with metals and other non-polymers. The researchers do not yet completely understand the physics behind the pillars forming but believe they arise from an interplay between the electrostatic attraction of the mask and the hydrodynamic instability of the polymer. ONR supports this and other research in multifunction electronics for intelligent naval systems.