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Scientists Report Single-Molecule Electroluminescence

Photonics Spectra
Oct 2002
Paula M. Powell

Building on earlier research at Georgia Institute of Technology in Atlanta that demonstrated the optical storage potential of thin films containing silver nanoclusters, one of the scientists from that study has coaxed photon emissions from individual silver molecules. This is reportedly the first demonstration of induced electroluminescence from individual molecules of such a material.

Multicolored electroluminescence from single silver molecules (B) resulted when Georgia Tech researchers applied 9 VDC across a discolored silver oxide film (A) placed between copper electrodes on a glass substrate in a vacuum. The molecules blinked and demonstrated dipole emission patterns (C). © 2002 National Academy of Sciences, USA.

Working with colleagues Tae-Hee Lee and Jose I. Gonzalez, Robert M. Dickson, an assistant professor in the school of chemistry and biochemistry, exposed thin films of initially conductive, nonelectroluminescent silver oxide to 1 mA AC. This induced emission from single silver molecules that, upon examination, blinked and demonstrated dipole emission patterns.

Overall color of the emitted light varied with the size of the metal nanoclusters involved. Although DC voltage also produced luminescence, the use of alternating current with voltage at frequencies above 150 MHz fueled a response up to 10,000 times greater. This was a direct result of the improved efficiency of converting electrical current to light, which increased the operating life of the emitting clusters.

Also of note was the resonance seen at the relatively high frequencies, something that suggested to Dickson that more information might eventually be processed in a given amount of time within a nanosystem playing off the luminescent capability of individual molecules. The principle is analogous to computer processing, where an 800-MHz processor is significantly faster than a 200-MHz one.

Another important result of the experiment was the demonstration of electroluminescence in clusters of copper molecules, which has somewhat of a twofold significance. "There are two issues here," Dickson said. "The first is that the effect occurs in systems other than silver, and the second, that it occurs in copper, which is used in computer chips to transport electrical signals. Thus one possible use of the electroluminescence capability of copper would be within optical interconnects on such chips."

One of the project's near-term goals is to explore the wiring of the molecules within simple circuits. "Benefits," Dickson said, "would be molecular or nanoscale electronics in which we might be able to accurately control charge transport through individual molecules. This would help shrink electronic components to molecular dimensions and potentially allow the utilization of discrete states to control information transfer." He noted that the most difficult issues will probably be the fabrication of multiple electrodes with nanometer spaces, as well as the capability to accurately control the junctions of molecules to electrodes.

The scientists stress that this research is still in the early stages. With further understanding of the process, however, they may someday be able to fine-tune it for use in a variety of simple nanoscale devices, quite possibly even in light-emitting diodes.

Basic ScienceResearch & Technology

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