Switching the Current Flowing Through a Molecule On or Off


Scientists Flip Molecular Switch
by Diane Kightlinger


November 1, 2000

Back in 1959, Richard P. Feynman - then a Caltech professor and later a Nobel Laureate in physics - predicted the field of nanotechnology in a lecture entitled "There's Plenty of Room at the Bottom." Decades later, we're just beginning to realize the potential that nanotechnology offers. Although the prospect of ultra-dense computer memories and cell-sized robots fires plenty of imaginations, working on the scale of a billionth of a meter poses enormous challenges.

Scientists have succeeded in creating molecules that function like conventional electronic components, but integrating the molecules into nanoscale devices requires control of electron flow across them. This week's issue of Nature presents one solution: a reversible molecular switch developed by David Schiffrin and colleagues in the Center for Nanoscale Science at the University of Liverpool, U.K.

"If we're to have computers that run on molecularly sized objects, we need to control the current," said Dan Feldheim of North Carolina State University. "That's what the Schiffrin paper shows - that there's a way to switch the current flowing through a molecule on or off."

Electronic switch design often limits the size of integrated circuits, and electronic engineers strive continuously to make them smaller. But to create their molecular switch, Schiffrin's team worked from the bottom up.

"Our approach was to develop a switch of very small dimensions by chemically synthesizing components and then putting them together," said Schiffrin.

The group linked a 6-nanometer-wide gold nanoparticle to a gold electrode, using wires consisting of up to 60 individual organic molecules. The molecules make up a "redox group" - a group into which the scientists can inject electrons. Adding electrons lets current flow from the electrode and up the molecular wire to the nanoparticle; removing electrons stops it. In other words, the wires act just like a switch to turn the current on or off.

To solder the molecular wires between the gold electrode and nanoparticle, the researchers attached "thiols" to both ends These sulfur atoms stick to any nearby gold surface, making it possible for the switches to assemble themselves. That capability will likely be crucial in nanoscale manufacturing.

The work of Schiffrin and his team adds another piece to the understanding of nanoscale electronic structures and their applications.

"We've demonstrated that you can control the flow of electrons across these structures," said Schiffrin. "Now we're at the next stage - figuring out how to transform them, to interconnect them, to produce functional circuits."

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