Feb 27, 2014
Electrolyte gate advances molecular electronics
One of the main challenges in fabricating transistors from single molecules is being able to place a gate electrode close enough to the molecular junction in a device. Now, researchers at Columbia University in the US say that using a liquid electrolyte instead of a solid one as the gate electrode could overcome this problem. The discovery could be an important step forward for molecular electronics devices that have the potential to be smaller and more tunable than conventional transistors and logic gates.
Most electronic devices are made from semiconductors such as silicon. However, some single molecules appear to have electronic properties similar to traditional semiconductors and can be used to make electronic devices in their own right. The main advantage of such devices is that molecules are extremely small compared with semiconductor structures.
Single-molecule electronics have advanced significantly since they were first put forward in the 1970s, but it still remains very difficult to electronically couple single molecules to a metal gate electrode to make fully functioning transistors. Now, a team led by Latha Venkataraman has found that a soluble electrolyte gate can be used to modulate the conductance of a non-redox active molecule in a molecular device. “Our discovery means that we can now tune the conductance of single-molecule devices without having to lithographically fabricate a metal gate electrode – which needs to be about the same size as that of the molecule actually used to make the device,” Venkataraman told nanotechweb.org.
Fabricating electrolyte gate transistors much easier
In their experiment, the researchers simply submerged the source and drain electrode of the device in an electrolyte solution. They then contacted this solution with a third, gate electrode that can be as far away as millimetres from the molecular junction but can still be used to tune the junction’s conductance, explains Venkataraman. A voltage is applied to the gate electrode to drive the ions in the electrolyte to the junction.
“Being able to gate a molecular junction is crucial for developing molecular transistors,” said team member Brian Capozzi. “While lithographically defining a source, drain and gate electrode to create a molecular transistor is challenging, fabricating electrolyte gate transistors would be much easier.” Indeed, we might even employ ionic liquids, which are not volatile and are becoming more and more popular in such applications, as a more permanent gate dielectric, he adds.
The team says that it is now busy optimizing the gating efficiency in its single-molecule devices so that the gate bias produces a greater molecular conductance change. “In the same vein, we would like to study molecules that react even more dramatically to changes in gate potential,” said Capozzi.
The current work is detailed in Nano Letters DOI: 10.1021/nl404459q.
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About the author
Belle Dumé is contributing editor at nanotechweb.org