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13 Apr 2007
An interdisciplinary team of researchers in the US has built one of the smallest organic light-emitting devices to date.
The microscopic "nanolamp" is made of synthetic nanofibres just 200 nm wide and could find applications in flexible electronics, which are increasingly being made smaller, and sensors.
The fibres are made of a compound based on the metal ruthenium and are smaller than the wavelength of light they emit. Such a localized light source could be useful in applications ranging from sensing and microscopy to flat-panel displays and lab-on-a-chip devices.
Using a technique called electrospinning, José Moran-Mirabal and colleagues at Cornell University spun the fibres from a mixture of the metal complex, ruthenium tris-bipyridine, and the polymer, polyethylene oxide. The researchers observed that the fibres emitted orange light when excited by low voltage of about 3-4 V applied through micropatterned electrodes, rather like a tiny light bulb.
"Imagine you have light bulb that is extremely small," said team member George Malliaras, who is director of the Cornell Nanoscale Facility. "Then you can use the bulb to illuminate objects that you wouldn't be able to see otherwise."
Moran-Mirabal explained that the electrospinning technique is like pouring syrup on a pancake that is rotating. As the syrup is poured, it forms a spiral pattern on the flat pancake, which in this case is the substrate with micropatterned gold electrodes. The syrup is the solution containing the metal complex-polymer mixture in a solvent. A high voltage between the microfabricated tip and the substrate ejects the solution from the tip and forms a stretched, thinned jet. As the solvent evaporates, the fibre hardens on the substrate.
"As scientists look for ways to innovate - and shrink - electronics, there is much interest in organic light-emitting diodes because they hold promise for making panels that can emit light but which are also flexible," said Moran-Mirabal.
The new work shows that these light-emission devices can be made using relatively simple fabrication methods. Compared with conventional high-resolution lithography techniques, in which devices are attached onto pieces of silicon, electrospinning is much simpler.
"The current interest is in the ease with which this material can be made into very small light-emitting fibres," said team leader Harold Craighead, who is director of the Nanobiotechnology Center. "Its ultimate utility, I think, will depend on how well it stands up to subsequent processing and use."
The researchers reported their work in Nano Lett..
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