ARCHIVED - Nano-Charged: NINT Researchers Create the World's First Single Molecule Electrical Circuit

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August 05, 2005— Ottawa, Ontario

Researchers at National Research Council's National Institute for Nanotechnology (NINT) are discovering how to build the computer of the future one molecule at a time. A breakthrough in creating a single molecule electrical circuit was published in Nature on June 2, 2005. This discovery could pave the way to miniaturizing computers and creating sensors fine enough to detect single molecule interactions.

Computer miniaturization is currently limited by the size constraints of transistors. Each transistor has three electrodes, or electron conducting devices, which must be in physical contact to allow electricity to flow. Having three electrodes touching a single molecule is almost physically impossible, so a team led by Dr. Robert Wolkow at NINT did the next best thing - they made two electrodes serve as three.

Representation of charge conduction through the styrene molecule.
Representation of charge conduction through the styrene molecule.

"The present invention is a proof of concept that shows that a molecule's conduction characteristics can be switched [on and off] by a single electron placed adjacent to it," said Wolkow.

Dr. Wolkow's team took advantage of the fact that organic styrene molecules organize themselves in neat rows along a silicon 'floor'. The self organization processes automatically juxtaposes a negatively charged silicon atom at the end of a row of styrene molecules.

The presence of that single extra electron on the silicon atom next to the molecule caused electrons to flow from the tip of the STM through the adjacent styrene molecule and out the silicon floor. This has led to a new type of circuit.

"It's a pretty close analogy to a lift bridge," explained Wolkow. "A car attempting to drive over a valley can't do so until the lift bridge comes down to the level of the roadway. When that happens the car drives across."

Using the lift bridge analogy, the car is the electrical charge emitted from the tip of the STM, the styrene molecule is the bridge and the neighbouring silicon atom carrying the electron charge is the controller that determines whether the bridge is level with the roadway (on) or up in the air (off).

The scanning tunnelling microscope played a significant role in this discovery. "It's unlike any conventional microscope; it doesn't have any lenses or an eyepiece that you look through," explained Wolkow. "It actually is more like a record player. It involves moving a very fine tip around and charting the topography of the surface. If you had a single atom at the end of your probe, you could chart out topography on the atomic scale."

The STM bombards surfaces with electrons to measure their height and is sensitive enough to detect molecules. The NINT team used the STM to produce the electrical charge as well as track the charge's path through the styrene molecule. The STM is therefore an integral part of the molecular circuit, a liability that will have to be overcome to create a useful product from this discovery.

Standing: Jason Pitters, Gino DiLabio, Stanislav Dogel, Mohamed Rezeq. Seated: Janik Zikovsky, Paul Piva, Robert Wolkow
Standing: Jason Pitters, Gino DiLabio, Stanislav Dogel, Mohamed Rezeq. Seated: Janik Zikovsky, Paul Piva, Robert Wolkow

Dr. Wolkow's team is looking forward to engineering their nano-circuit for applications in computer and medical technology. Computers contain millions of transistors that turn on and off, allowing the processor to perform logic functions. Current transistor technology needs approximately one million electrons to switch the electrical state of a single transistor, using lots of power and generating significant waste heat.

"We're trying to initiate multiples of these single molecule units to make a prototype of a very simple integrated circuit of molecules," said Wolkow. "Being able to use just one electron would imply enormous speed advantages and power savings. A computer would run on almost nothing."

"The other thing we want to do is turn it into some kind of sensor to be used in a medical diagnostic device," said Wolkow.

Since their molecular conductivity device can turn itself on and off with the movement of a single electron, it could become the ultimate biological sensor capable of detecting when a single molecule attaches to a receptor on a cell.

Dr. Wolkow credits NINT's multi-disciplinary approach and its relationship with the University of Alberta for enabling this discovery. As Canada's flagship nanotechnology institute, its unique multidisciplinary environment integrates the forces of researchers from NRC and the University of Alberta across numerous disciplines. Established in 2001, NINT is a joint initiative of the Government of Canada, the Government of Alberta, the NRC and the University of Alberta.

"NINT is designed to put people of different disciplines together. That's what I'm trying to use now to call on my colleagues in the institute who have very diverse backgrounds," said Wolkow. "I'm hoping that through these interactions we can together come up with something that I wouldn't have been able to do on my own."

Dr. Wolkow credits his colleagues Gino DiLabio and Jason Pitters as well as post-doc Paul Piva along with the rest of the team for mastering the quantum mechanics, performing the precise measurements and having the stamina to see the project through.

The team has a patent pending on the transistor and detector concept. However, more basic research is needed to solve a few theoretical and practical puzzles before this discovery can be commercialized. Dr. Wolkow hopes that this discovery is just the beginning of a life-long exploration of the world on the nano-scale.

"If I'm lucky enough to be working in this area in 40 years I'll still have a full plate," said Wolkow. "I just can't imagine getting all the things done I want to get done in a short lifetime. Trying to bridge the gap from the nanoscale to the macroscale that you ultimately have to bridge to be able to use these things is a big challenge. "

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