Tuesday, September 04, 2007

A New Type of Molecular Switch

Continued from page 1

By Duncan Graham-Rowe

To switch the molecule, the group used a scanning tunneling microscope (STM) operating at extremely low temperatures and in a vacuum. However, the reaction is driven electrically, albeit at picoamps, so the STM is not necessary for this reaction to take place, says Liljeroth. But the low temperature could be a major obstacle to making the process practical.

For this particular molecule, the temperature had to be maintained at just five degrees kelvin in order for the reaction to occur in a controlled way. "The reaction still occurs at room temperature," says Liljeroth. "But at room temperature, it would happen spontaneously." Nevertheless, he says, the potential is there to find new molecules that exhibit this behavior at higher temperatures in the hope of eventually building logic devices.

Demonstrating that one molecular switch can be turned on and off by applying a current to a neighboring molecule is a first step toward such logic. "The ability to apply a voltage to one molecule and cause tautomerization of a neighboring one has interesting implications for logic devices," says Stoddart. But, he says, the temperature constraint remains a huge challenge.

Stoddart also rejects the IBM group's dismissal of molecular switches that change shape; he argues that such molecules are at a much more advanced stage and can operate at room temperature. "I find it galling that scientists in the field of molecular electronics continue to be unfairly dismissive of research by others that is much more technologically advanced than their own, and yet also has a very sound theoretical and experimental basis to it."

Yale's Reed is also skeptical about the practical implications of the IBM finding. Any talk of turning this reaction into a device amounts to "excessive hyperbole" at this stage, he says. "It's like saying we have discovered silicon semiconductors, therefore we can make a Pentium."