Scientists Develop Method for Generating Small, Ultradense Polymer Films
Feb 23, 2009
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Scientists at the University of Massachusetts Amherst at University of California-Berkeley have developed a faster, more efficient way to produce defect-free thin polymer films with the smallest domains ever achieved and ordered in the densest way possible for any given size—-to dramatically improve storage density.

Tom Russell, a leading expert on polymer behavior and director of the UMass Amherst Materials Research Science and Engineering Center, with colleagues there and at the University of California Berkeley, created a new technique for guiding self-assembly of block copolymers—-two chemically dissimilar polymers joined together--that they say should not only increase data storage volume, but will save months in manufacturing and open up vistas for entirely new applications. The density achievable with the technology they’ve developed could allow the contents of 250 DVDs to fit on a surface the size of a quarter, for example.

For the base layer, Russell and his colleagues used commercially available sapphire wafers, which start out flat. Heating them from 1300 to 1500 degrees Celsius for 24 hours causes the surface to reorganize into a sawtooth topography with an inherent orientation. So when a thin copolymer film layer is applied, the underlying corrugations or crystal facets guide the film’s self-assembly in a highly ordered way to form an ultradense hexagonal or honeycomb lattice.

"We can generate nearly perfect arrays over macroscopic surfaces where the density is over 15 times higher than anything achieved before," Russell says. "We applied a simple concept to solve several problems at once, and it really worked out."

By varying the annealing temperature, the scientists say they can change the angle and height of the saw teeth and the depth of the troughs between peaks. Most previous efforts to create a well-ordered substrate or bit-patterned media, as it’s known, were stuck at 15 nanometers for the smallest achievable pattern size, Russell explains. But "we’ve shattered that barrier and I think we can go farther," he adds.

In addition, in the past there had not been a way to characterize, or precisely measure, a large area of these structures on the nanoscopic level because each time a measuring device is moved, accuracy is lost. But for the first time, Russell and his team say they solved the problem using grazing incidence X-ray scattering. "We’ve essentially established a new technique," Russell says, for characterizing large-scale arrays with nanoscopic precision.

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