Posted: April 11, 2007 |
Researchers create 'nanolamps' - smallest organic light-emitters |
(Nanowerk News) To help light up the nanoworld, a Cornell interdisciplinary team of researchers has produced microscopic "nanolamps" -- light-emitting nanofibers about the size of a virus or the tiniest of bacteria.
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In a collaboration of experts in organic materials and nanofabrication, researchers have created one of the smallest organic light-emitting devices to date, made up of synthetic fibers just 200 nanometers wide. The potential applications are in flexible electronic products, which are being made increasingly smaller.
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The fibers, made of a compound based on the metallic element ruthenium, are so small that they are less than the wavelength of the light they emit. Such a localized light source could prove beneficial in applications ranging from sensing to microscopy to flat-panel displays.
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An illustrated closeup of an electrospun fiber. During experimentation the organic devices gave off an orange glow. (Image: Cornell University)
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The work, published in the February issue of Nano Letters, was a collaboration of nine Cornell researchers, including first author José M. Moran-Mirabal, an applied physics Ph.D. student; Héctor Abruña, the E.M. Chamot Professor of Chemistry and Chemical Biology; George Malliaras, associate professor of materials science and engineering and director of the Cornell NanoScale Facility; and Harold Craighead, the C.W. Lake Jr. Professor of Engineering and director of the National Science Foundation-funded Nanobiotechnology Center.
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Using a technique called electrospinning, the researchers spun the fibers from a mixture of the metal complex ruthenium tris-bipyridine and the polymer polyethylene oxide. They found that the fibers give off orange light when excited by low voltage through micro-patterned electrodes -- not unlike a tiny light bulb.
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"Imagine you have a light bulb that is extremely small," said Malliaras, an organic materials expert. "Then you can use the bulb to illuminate objects that you wouldn't be able to see otherwise."
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Craighead's research group, which focuses on nanostructures and devices, supplied the expertise on the electrospinning technique.
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The technique, explained Moran-Mirabal, who works in Craighead's laboratory, can be compared with pouring syrup on a pancake on a rotating table. As the syrup is poured, it forms a spiraling pattern on the flat pancake, which in electrospinning is the substrate with micropatterned gold electrodes. The syrup would be the solution containing the metal complex-polymer mixture in solvent. A high voltage between a microfabricated tip and the substrate ejects the solution from the tip, Moran-Mirabal said, and forms a jet that is stretched and thinned. As the solvent evaporates, the fiber hardens, laying down a solid fiber on the substrate.
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As scientists look for ways to innovate -- and shrink -- electronics, there is much interest in organic light-emitting devices because they hold promise for making panels that can emit light but are also flexible, said Moran-Mirabal.
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"One application of organic light-emitting devices could be integration into flexible electronics," he said.
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The research also shows that these tiny light-emission devices can be made with simple fabrication methods. Compared with traditional methods of high-resolution lithography, in which devices are etched onto pieces of silicon, electrospinning requires almost no fabrication and is simpler to do.
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The durability of organic electronics is still under investigation, and this recently completed research is no exception, Craighead said.
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"The current interest is in the ease with which this material can be made into very small light-emitting fibers," he said. "Its ultimate utility, I think, will depend on how well it stands up to subsequent processing and use."
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