Simple Optoelectronic Devices Based on Silver Nanoclusters Perform Logic Operations

Based on arrays of individual electroluminescent silver nanoclusters, the quantum devices could provide a foundation for new forms of specialized molecular-scale computing. The research, sponsored by the National Science Foundation, is reported in the March 18 issue of the journal Proceedings of the National Academy of Sciences.
"In effect, we are demonstrating optoelectronic transistor behavior," said Robert Dickson, a professor in Georgia Tech's School of Chemistry and Biochemistry. "Instead of measuring current output as in standard electronic transistors, we measure electroluminescent output for a given voltage input. Our devices act in a way that is analogous to a transistor with light as the output instead of electrical current."
Because the nanoclusters possess different energy levels, they can be addressed individually by varying the voltage injected into the array of clusters with a simple two-terminal system. Avoiding the need for isolated electrical connections to each nanocluster makes the system far easier to fabricate at the nanometer scale than electronic devices of traditional design.
Key to the new devices developed by Dickson and collaborator Tae-Hee Lee is the specific voltages at which the clusters - which contain between two and eight silver atoms - emit light when electrically excited.
To operate, the devices require at least two separate electrical pulses, which can be varied in amplitude. Electroluminescence occurs only after the second pulse, which activates nanoclusters within the array depending on the voltage level to which each one responds. Because each nanocluster only responds to very specific voltages, the combined current delivered by the pulses activates only specific clusters, which are observed optically.
"By reading the emission output of two correlated molecules, we can add pulses together and perform a very simple but very important basic addition operation," Dickson noted. "The response is relatively narrow. Only when you have exactly the right voltage do you get a response. We see really clean on-off behaviors with this system."

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