New look for molecular transistors
Mar 31, 2005
Theoretical physicists in the US have proposed a new way to make a single-molecule transistor. David Cardamone, Charles Stafford and Sumit Mazumdar at the University of Arizona say the quantum interference effect transistor could be a realistic way to extend existing transistor technology down to the nanoscale (arXiv.org/abs/cond-mat/0503540). The device modulates the flow of current through a hydrocarbon ring by switching quantum interference "on" and "off".
In the quantum regime, particles can act like waves and interfere with each other. However, this quantum interference vanishes as we approach macroscopic length scales as the particles begin to interact with their environment. Physicists usually try to avoid this phenomenon, known as decoherence, when designing and building quantum devices. However, in the quantum interference effect transistor (QuIET) decoherence would act as the "knob" that controls the flow of current through the device.
The QuIET consists of two electrodes attached to an organic ring molecule, such as benzene, in the so-called meta positions on the ring. In this configuration, quantum interference completely suppresses current flow through the molecule and the transistor is effectively "off". The device is switched "on" when the decoherence caused by a third electrode causes the quantum interference to disappear.
The Arizona team proposed two different ways of switching on the device: bringing the tip of a scanning tunnelling microscope close to the molecule, or attaching an acceptor or donor molecule to it via a short molecular "bridge" (see figure). In the latter approach a nearby gate electrode controls the decoherence through the polarization of this molecule.
"The technology needed to construct this device already exists," Cardamone told PhysicsWeb. "Both the scanning tunnelling microscope and the mechanically-controllable break junction techniques have already been used to contact individual molecules in a two-terminal configuration. We simply propose combining these techniques to make a three-terminal device."
One potential advantage of the QuIET approach is that it could work in aqueous environments, such as those inside living organisms, because it is made of organic molecules. The Arizona team are discussing how to make the devices with experimental colleagues.
About the author
Belle Dumé is Science Writer at PhysicsWeb