QuIET molecular transistors

Physicists from the University of Arizona think they've found a way to use single molecules as working transistors. They thought about making transistors as small as a nanometer by looking at quantum mechanics. This transistor, called Quantum Interference Effect Transistor (QuIET) will not power nanocomputers before at least a dozen years. But read more...

Physicists from the University of Arizona think they've found a way to use single molecules as working transistors. As traditional transistors will not shrink much smaller than 25 nanometers, they thought about making transistors as small as a nanometer by looking at quantum mechanics and using benzene, a ring-like molecule. They even have applied for a patent for this transistor, called "Quantum Interference Effect Transistor," or 'QuIET' for short. But the arrival of such ultrasmall transistors is not scheduled before at least a dozen years, so don't dream today of nanocomputers or nanorobots traveling inside your bodies. Read more...

Here is the first paragraph of the University of Arizona news release, which obviously has learned something from PR people.

University of Arizona physicists have discovered how to turn single molecules into working transistors. It's a breakthrough needed to make the next-generation of remarkably tiny, powerful computers that nanotechnologists dream of.

The physicists, which include Charles Stafford and Sumit Mazumdar, realized several years ago -- as many other people in the field also did -- that the current approach to develop transistors was reaching its physical limits. And they "realized that quantum mechanics [could] solve the problem of how to regulate current flow in a single-molecule transistor that would work at room temperature." This led to their Quantum Interference Effect Transistor.

Below is an artist's conception of this Quantum Interference Effect Transistor (QuIET). "The colored spheres represent individual carbon (green), hydrogen (purple), and sulfur (yellow) atoms, while the three gold structures represent the metallic contacts. A voltage applied to the leftmost contact regulates the flow of current between the other two." (Credit: University of Arizona/Nano Letters) (Link to a larger version)

An artist's conception of QuIET

So how will this work?

The simplest molecule they propose for a transistor is benzene, a ring-like molecule. They propose attaching two electrical leads to the ring to create two alternate paths through which current can flow. They also propose attaching a third lead opposite one of the electrical leads. Other researchers have succeeded in attaching two contacts to a molecule this small, but attaching the third is the trick -- and the point. The third lead is what turns the device on and off, the "valve."
"In classical physics, the two currents through each arm of the ring would just add," Stafford said. "But quantum mechanically, the two electron waves interfere with each other destructively, so no current gets through. That's the 'off' state of the transistor." The transistor is turned on by changing the phase of the waves so they don't destructively interfere with each other, opening up additional paths through the third lead.

It will probably take a dozen years or more before nanocomputers can be built. But according to one researcher, such nanocomputers could have a major impact in medicine.

"These machines could operate in solution, in vivo. There already are clinical trials of nanoparticles to deliver medicinal drugs. Imagine how much more powerful those little nanoparticles or nanorobots would be if they could count, or do simple computation. With our transistors packed at maximum density, you could put a microprocessor as powerful as the top-of-the-line workstation on the back of an E. coli," [said David Cardamone, who received his doctorate from UA in 2005.]

This research work was published online by Nano Letters in July 2006 under the title "Controlling Quantum Transport through a Single Molecule" and should appear as the cover story of the November printed version of the journal. Here are two links to the abstract and to the full paper (PDF format, 5 pages, 152 KB).

Sources: University of Arizona news release, August 30, 2006; and various web sites

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