The UA researchers realized quantum mechanics could answer how to regulate current flow in a single-molecule transistor at room temperature

The trick about transistors.

A transistor switches electrical current on and off just like a valve turns water on and off in a garden hose. Industry now uses transistors as small as 65 nanometers, but the UA physicists’ work could result in transistors as small as a single nanometer, or one billionth of a meter.

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.

"All transistors in current technology, and almost all proposed transistors, regulate current flow by raising and lowering an energy barrier," Stafford said. "Using electricity to raise and lower energy barriers has worked for a century of switches, but that approach is about to hit the wall."

Transistors can't shrink much smaller than 25 nanometers, or 1/40,000 the width of a pinhead, because scaling down further creates intractable energy problems, Stafford said. Even if it were possible to build an ultra-advanced laptop computer with molecule-sized transistors using current transistor technology, it would take a city's worth of electricity to run the laptop, and the thing would get so hot it would probably vaporize.

UA’s Charles Stafford, Sumit Mazumdar and David Cardamone, began thinking about the problem of next-generation transistor technology three years ago. They realized that quantum mechanics can solve the problem of how to regulate current flow in a single-molecule transistor that would work at room temperature.

"It took a while to go from the idea of how this could work to developing realistic calculations of this kind of system," Stafford said. "We were able to do the simplest kind of quantum chemical calculations which neglect interactions between different electrons within a few weeks. But it took some time to put in all the electron interactions that demonstrate this really is a very robust device."

"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."

"Our approach is a little more finesse than brute force," UA’s Cardamone added. "We don't put up a wall to stop current. It's just that we can regulate how electron waves combine to turn the [atomic-scale] transistor on or off." As an example, with QuIET, various atoms are afiixed with gold metallic contacts. A voltage applied to these contacts regulates the flow of current between atoms. 

One molecule the UA team 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.

No nanocomputers very soon

According to the Semiconductor Research Corp. it typically takes a dozen years for a new idea to go from initial scientific publication to commercial technological application, Stafford noted.

"That means if the computer industry is to continue its recent pace in making smaller-scale computers, we should have had this idea yesterday, " Cardamone said.

Why all this effort to make incomprehensibly small computers? Why expend so much brainpower on nanocomputing?  More computing power will result in more realistic simulations, whether you're a scientist modeling global warming or supernovae explosions, or an entertainment industry animator creating believable emotion in a simulated human face, Stafford said.

The American Chemical Society "Nano Letters" published the researchers' technical article.