AMHERST, Mass. -- A UMass polymer scientist is among the researchers reporting a major step forward in nanoscopic pattern transfer in the Feb. 24 issue of the journal Nature. Tom Russell, polymer science and engineering, and postdoctoral researcher Thomas Thurn-Albrecht collaborated with Ullrich Steiner and graduate student Erik Schaffer of University of Groningen, The Netherlands. The findings have implications in paving the way for still-smaller integrated circuits, magnetic storage in computers, and on-chip sensors; all of this without the use of chemicals.
Scientists aim to produce devices so small that they can only be seen with electron or atomic-force microscopes. Russell specializes in polymers -- long, linked strands of molecules that can be custom-designed to offer properties ranging from the softness of silk to the hardness of rubber. The National Science Foundation and the U.S. Department of Energy fund his work in this area.
Schaffer and Thurn-Albrecht began by placing a thin film of polystyrene -- the same material from which disposable coffee cups are manufactured -- atop an electrode. A second electrode was placed above the film, leaving an air gap between the film and the top electrode. The polystyrene was then heated, liquefying it, and a small voltage was placed on the electrodes. With time, the surface of the film appeared pockmarked. What essentially occurred, Russell explained, is that the electric field amplified waves on the liquid's surface. The waves were increasingly amplified and eventually were pulled to the top electrode. The phenomenon shows up under the microscope as a dark ring on a light background. As time passed, more and more circles appeared. Strikingly, they were all the same size, and appeared at a precise distance from one another.
The phenomenon occurs, Russell says, because of the interaction of four competing forces. Those forces include: the electrical force, which pulls the liquid toward the top electrode; the surface energy of the liquid, which wants the liquid to lie flat; the viscosity of the liquid as crests and valleys form and the liquid moves; and the effects of atmospheric pressure. "It doesn't happen helter-skelter," explains Russell. "It happened at very distinct distances that represents a delicate balance between all of these forces."
Perhaps more importantly, the team can also "imprint" a film with a very specific design -- a process called pattern transfer. In pattern transfer, an electrode is etched with a master pattern. The master electrode has a topography of "hills" and "valleys." When a voltage is applied, the film responds most strongly to the closest portions of the electrode, creating a replica of the master's design on the polymer film.
Note: Tom Russell can be reached at 413/577-1516 or Russell@mail.pse.umass.edu Images are available at www.umass.edu/newsoffice
Journal
Nature