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Making electronic devices in which performance is controlled by a single molecule seemed like a far-fetched idea just a few years ago. But since then, scientists have created circuits and simple devices based on a single carbon nanotube, a C60 molecule, and other molecules.
IN THE GAP Single-molecule electronic devices are based upon the properties of a lone molecule trapped in a nanosized gap between electrodes. A Harvard-Berkeley team prepared devices based on a complex with two vanadium atoms (top), while a Cornell team studied cobalt-terpyridinyl complexes (bottom).
Now, two research groups independently report taking another key step toward creating tomorrow’s molecular electronic devices. The scientists fabricated and tested transistors in which one molecule of a transition-metal organic complex bridges the nanometer-scale gap between the devices’ electrodes and dictates their electronic properties. prepared a triazacycloalkyl complex containing two vanadium atoms and trapped the molecule between the electrodes of a microscopic transistor. Because there is no simple method for directly imaging a lone molecule sitting between a pair of electrodes, both research groups measured electrical conductance properties of their specimens and showed that the devices exhibit single-molecule signatures. The teams also showed that the nanostructures indeed behave as transistors in that the flow of electrical current can be turned on or off by controlling the voltage on an electrode known as a gate. team observed a Kondo resonance and found that the effect could be controlled by using the gate voltage to tune the charge and spin state of the vanadium complex.
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