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Nanoscientists Describe Electron Movement Through Molecules

September 30, 2005
Ohio University
Molecular electronics is the ultimate miniaturization of electronics. In this area of research, scientists have been studying the movement of electrons through individual molecules in an effort to understand how they might control and use the process in new technologies.

This illustration displays the conductance through the molecule as a color map (blue is low value, yellow and red are higher). The conductance tells scientists how easily a current can pass through the molecule.
Credit: Sergio Ulloa

ATHENS, Ohio — Molecular electronics is the ultimateminiaturization of electronics. In this area of research, scientistshave been studying the movement of electrons through individualmolecules in an effort to understand how they might control and use theprocess in new technologies. Computers and thousands of other devicescould become vastly faster, smaller and more reliable than conventionaltransistor-based (wire-based) electronics.

A team of OhioUniversity and Brazilian physicists has taken another step toward thisgoal. In the Rapid Communication section of the Sept. 15 issue of thejournal Physical Review B, the researchers present a new theory of howelectrons interact in a molecule.

In the new paper, the teamdescribes what happens to electrons when scientists put two moleculesbetween electrodes, which are bits of tiny conducting wire. Existingtheoretical models of molecular electronics take into account thatelectrons avoid each other, according to Nancy Sandler, Ohio Universityassistant professor of physics and astronomy. The scientists reportthat molecular vibrations, in addition to strong electronicinteractions, will produce unexpected “transport channels.” Theelectrons move through the molecule while the molecule vibrates, saidSergio Ulloa, co-author of the paper and Ohio University professor ofphysics and astronomy.

“The electrons go through the moleculelike a pinball and they leave all the bells ringing (atoms moving) asthey pass by,” said Ulloa, adding that this model focuses on thegeneral behavior of short molecules. Other scientists studyingmolecular electronics, he noted, are using longer molecules, such asDNA or carbon-based molecules, to serve as longer “wires” or connectors.

Thecollaborators on this project – which included Ulloa, Sandler,Brazilian exchange student Edson Vernek and professor Enrique Anda ofthe Pontifícia Universidade Católica in Rio de Janeiro, Brazil –describe another fascinating capability of the electrons: “Theelectrons ‘remember’ not only where they are, but where they havebeen,” Ulloa said. “When the oscillations of the molecules are ‘justright,’ the electrons are either pushed through more efficiently ortrapped momentarily in the molecule – a phenomenon physicists call‘Rabi-assisted tunneling.’ The electrons can really get trapped, likein the pinball machine.”

This electron “trapping” could makemolecular transmission even more efficient and help develop molecularswitches and other applications.

Molecular electronics is abooming field in physics right now. Scientists have been able tomanipulate molecules for only last 15 years, Sandler said, and it maybe at least another 20 years before consumers see molecular technologyin commercially available devices.

The research collaborationbetween Ohio University, the Pontifícia Universidade Católica in Rio deJaneiro, Brazil, and the Universidad de Buenos Aires, Argentina, issupported by the National Science Foundation through the project“Correlation Effects and Transport in Nanostructured Materials.” TheBrazilian Coordination of Improvement of the Personnel of SuperiorLevel (CAPES) supported Vernek’s visit to Ohio University.

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Materials provided by Ohio University. Note: Content may be edited for style and length.

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