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  May 8, 2000

Researchers Develop Spiral Wires
that are Excellent Semi-Conductors

UConn chemical researchers have produced stable helical wires that are excellent semiconductors from an inorganic material - manganese oxide. These helices, which can range in size from 3 mm wide and 12 inches long to as small as micron-thick strands, may usher in a new generation of conducting material for the electronics industry.

As more specifics are learned about the novel features of these wires - they can alter their structure while preserving their shape, are porous, and have excellent optical transparency - the knowledge may lead to a host of potential applications in computers and materials science.

UConn's Center for Science and Technology Commercialization recently filed a U.S. patent application for the wires.

The discovery was reported in the May 4 edition of the journal Nature, by Steven Suib, a professor of chemistry, and his research team of graduate students and postdoctoral associates: Oscar Giraldo, Stephanie Brock and Manuel Marquez. Other collaborators were Hugh Hillhouse and Professor Michael Tsapatsis of the University of Massachusetts/Amherst, Department of Chemical Engineering.

"This is probably the most exciting research I've ever been involved with," says Suib. "There is nothing like this currently known. Some unusual features include the helical morphology, the ability to change composition and preserve the helix, and the electrical conductivity."

Pursuit of new conducting wires through molecular engineering has been the focus of several laboratories nationwide. Thin films and wires are in great demand as sensors and conducting materials to enhance computing speed and storage density, and as effective membrane materials for separation.

Several synthetic approaches - such as entrapment of carbon and organic conducting polymeric materials or vapor deposition in porous media - have been used to produce wires. Attempts to remove such materials from hosts have been fraught with difficulty, however.

Suib says the research leading to the discovery of the helical wires of manganese oxide was a spin-off of work he and his team were conducting for the U.S. Department of Energy.

The researchers produce their wires of manganese oxide - a brittle grayish metallic mineral - in capillary tubes filled with a fluid colloidal solution. Heating causes the materials to "grow" into a gel. As the solvent evaporates, the gel shrinks and capillary force - the force of adhesion between the glass tube and the liquid solvent - causes it to buckle and expand into a helical (spiral) shape.

The composition of these wires is unusual. Suib's team has learned that helices are produced when high concentrations of the starting fluid solution are used, whereas the gel forms rings when the solution is diluted. "Most inorganic materials don't take this helical structure, and we're still not certain why this happens here," he says.

The wires can be removed by breaking the glass or using a water solvent. The wires are flexible enough to be wrapped around other objects.

"There are so many potential applications for these materials that it's hard to decide exactly what to pursue," Suib says.

A list of potential uses for the wires includes: batteries, magnetic devices, optical systems, catalysis, sensors, chromatography, imaging, semiconductors, lighting devices, fuel cells, switches, electrical conductivity devices, magnetic recording, coatings, adhesion protection, ceramics, slow release substrates in agriculture and pharmaceuticals, medical devices, and others.

Suib says pursuing the potential applications of the discovery will require considerable additional resources. "It is not clear how long it would take to develop any of these applications," he says. "This discovery has considerable fundamental interest and potential applications may have far-reaching effects."

David Bauman