Thursday, December 24, 2009

Researchers Show Off Functional Single-Molecule Transistor

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As semiconductor manufacturers continue to push down the size of their products' wiring, a number of research labs have started looking into whether they can simply take the process to its logical conclusion: a transistor made from a single molecule. A number of these items have been demonstrated, and they do manage to control the current flow through the molecular transistor, but they do so through a variety of tricks that have nothing in common with the methods used for the semiconductors in our electronics. In today's issue of Nature, an international team reports producing the first voltage-gated molecular transistors.

The basic principle behind a transistor is simple. All it needs is two electrodes, a source and a sink, and a gate that controls the flow of current between them. In semiconductor transistors, the gate contains a semiconductor and another electrode: raising or lowering the voltage in this electrode controls whether current can flow across the semiconductor between the source and sink.

For molecular transistors, the semiconductor is replaced by a single molecule. Electrons can flow through a variety of molecules, but controlling that process is not the easiest thing. A few of the past efforts have switched currents on and off by changing the charge on the molecule or playing with the spin of the electrons that pass through it, but these are difficult challenges in their own right, and far more complex than simply applying a voltage to the gate.

The new work involved creating a nanoscale gap in a gold wire that was placed directly above an aluminum oxide electrode that controls the gate. The gold had been covered with one of two types of molecules in advance and, once the gap was created, there was a chance that one of those molecules dropped into the newly vacated space, bridging the gap and enabling the molecule to conduct currents between the two gold electrodes.

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