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Tiny devices aid optical computing

12 Mar 2003

Optical computing could be one step closer thanks to nano-scale electroluminescent devices being developed in the US.

Two researchers in the US have made nanometer-scale optoelectronic devices that can act as logic gates. Robert Dickson and Tae-Hee Lee from Georgia Institute of Technology say their tiny electroluminescent devices could pave the way towards molecular-scale optical computing. (Proceedings of the National Academy of Sciences March 18)

"We are essentially demonstrating optoelectronic transistor behavior," said Dickson. "Instead of measuring current output as in standard electronic transistors, we measure electroluminescent output for a given voltage. Our devices act like transistors with light as the output instead of electrical current."

The duo's devices are based on so-called silver "nanoclusters", each cluster containing between 2 and 8 silver atoms. Crucially, Dickson and Lee found that the clusters emit light when they are electrically excited using a simple two-terminal system. As a result, individual electrodes are not needed for each nanocluster, making the logic circuits easier to fabricate.

The researchers induce electroluminescence by firing two electrical pulses at the clusters. Individual clusters respond to specific input pulses because of an internal system of discrete energy levels. Dickson and Lee have taken advantage of this internal structure to perform simple addition and logic functions.

"By reading the output of two correlated molecules, we can add pulses together," said Dickson. "The response is relatively narrow. Only when you have exactly the right voltage to you get a response. We see really clean on-off behavior with this system."

Applying different pulses can also cause individual clusters to operate as logic gates with AND, OR, NOT and XOR functions. Dickson says that increasing the number of clusters operating together could lead to large arrays capable of performing complex operations.

"If you can put molecules that have well-defined electronic energy levels into an array addressable with just two terminals, then you can begin to perform very complicated calculations," he said. Although Dickson does not expect the devices to replace computers for ordinary tasks, he does see a niche for them to carry out complex and specialized calculations.

But before the clusters find these real-life applications, Dickson and Lee are looking to gain more control over cluster's properties. At present, they only operate at room temperature for several hours before they burn out because they become too hot.

Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.

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