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23 Aug 2002
US scientists observe electroluminescence from individual molecules for the first time.
Scientists at the Georgia Institute of Technology, in the US, have demonstrated electroluminescence from individual molecules of silver. They reported their work in the Proceedings of the National Academy of Sciences.
"This is the first time that anyone has seen electroluminescence from individual molecules," said Robert Dickson of the Georgia Institute of Technology. "What we have observed involves sub-nanometre scale sources to which an electric field is applied. These molecules emit very strongly and are very robust."
The scientists took a thin film of silver oxide and treated it with an electrical current of about 1 A. This created a thin line of silver clusters of between 2 and 8 atoms. Under the influence of an alternating current these clusters exhibited electroluminescence, emitting light at a frequency that depended on their size.
Scientists usually stimulate electroluminescence by applying a direct current. In this study, however, the team found that a high-frequency (more than 150 MHz) alternating current produced an electroluminescence response that was 10,000 times as great as that produced by a direct current.
The researchers reckon that the alternating current creates rapid electron-hole recombination within single molecules in a very narrow section of the sample. Bulk materials, in contrast, cannot respond quickly enough to an alternating current for it to enhance the electroluminescence response.
"We are concentrating on understanding the fundamental aspects of this: what the nature of the emission is, how the emission occurs," added Dickson. "We need to know how improve our control of this before we can begin to use it in nanometre-scale devices or as nanometre-scale optoelectronic components in circuitry."
The researchers also demonstrated electroluminescence in nanoclusters of copper atoms.
Author
Liz Kalaugher is editor of Nanotechweb.
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