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Molecular Electronics Advances Two Steps Closer to Reality

The goal of molecular electronics¿fashioning electronic parts from single molecules joined together¿may now be two steps closer to reality. One group of researchers has created the most compact (and first self-assembled) organic molecule transistor yet, while another team has figured out how to measure the flow of electrons through single molecules accurately. The leaders of both groups say these advances should help physicists further explore the potential of molecular electronic devices.

To build their transistor, Jan Hendrik Sch¿n of Bell Laboratories in New Jersey and colleagues, who describe their findings in the current issue of the journal Nature, allowed many thousands of organic molecules to assemble themselves onto a gold film like bristles on a brush. By sandwiching another layer of gold on top and applying an electric field to this "meat" with a silicon electrode, the researchers created a transistor with a channel just one molecule¿about 10-20 Angstroms¿wide. "The first characteristics that we have seen for these devices are quite remarkable," Sch¿n reports. "Of course, that might not be good enough for real applications, but¿ so far we are quite optimistic that we can work this out."

Sch¿n says the next steps are to self-assemble molecules of different shapes to see which ones make the best transistors, and to see how far these devices can be scaled down. In the future, he notes, it may be possible to fashion sprawling molecules with parts that will replace the gold and silicon electrodes in the current setup.

But transistors are useless without wires, and researchers need to know which molecules will make the best wires. Enter Stuart Lindsay and colleagues at Arizona State University, who published their study today in Science. They, too, attached small carbon chains in bristle fashion to a layer of gold, but only some of these were able to bond to gold on both ends. The researchers could consistently measure the conductivity of these gold tipped molecules by brushing them with an atomic force microscope, also gold capped. Previous measurements in molecules like DNA would give conflicting results depending on how the measurement was made. Attaching gold to both ends is the key, Lindsay explains: "By tethering the molecule [to gold] you've removed a lot of the variability. It's night and day."

Lindsay says this technique will allow researchers to test the properties of different proposed molecular devices to see how they really behave. "Molecular electronics is something we can now do in earnest and feel good about as physicists.

The Incredible Shrinking Circuit, (Scientific American, September 2001) is available for purchase at the Scientific American Archive
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