A Sponge's Guide to Nano-Assembly

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"At first the crystals form at the [surface], but with time they begin to project down into the solution like stalactites growing down from the roof of a cave," Morse says. "What you end up with is a nanostructured thin film of semiconductor with very high surface area because of all the projecting thin plates or needles that project down into the solution."

The method works at low temperatures, about room temperature, whereas conventional techniques for making semiconducting thin films require a high temperatures -- 400 degrees Celsius, Morse says. It also does not require oft-used harsh acids and bases. In addition to making the process cheaper and easier, the mild conditions could lead to devices that incorporate materials that would be impossible to use with conventional processes. Sometimes, for example, the materials that can be used in a device are limited by the high temperatures used to make the materials. "If you can make them all at room temperature, then you may be able to dope them with dopants that you normally couldn't use at high temperature," says Angela Belcher, materials science and engineering and biological engineering professor at MIT, who finds Morse's work "very exciting."

Ultimately, the payoff from Morse's work studying biological mechanisms may be more than novel thin films, says Aravinda Kini, U.S. Department of Energy materials science and engineering programs manager. Although the current process works only for thin films, further understanding of the catalysis and templating methods of sponges could one day make it possible to fabricate complex machine parts by piecing together molecules. "It's still a dream, but imagine the blade of an aircraft engine being assembled from the bottom up, without any defects, without any very expensive fabrication methods," he says. "That's what is possible. That's what people are dreaming about."

Home page image courtesy of Kristian Roth, Birgit Schwenzer, and Daniel E. Morse, University of California, Santa Barbara.