http://www.sciencedaily.com/releases/2000/02/000225080330.htm
UMass Scientists Reports Nanotech Advance
Findings to be detailed in the journal Nature
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.
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