June 13, 2002 How small can electronic devices get? Nano-small! Two teams of scientists have fashioned transistors from single molecules, and report their results in the June 13 issue of Nature.
The ability to use individual molecules for electronics is a coveted breakthrough for science at the nanometer scale and for electronics industries because of the potential to shrink the size of components well beyond what is possible using conventional lithography techniques.
Transistors, traditionally made from silicon, regulate the transmission of electrons across barriers. The barrier height, and hence the electron flow, can be controlled by applying a small voltage to an electrode that acts as a gate. At the Cornell University Center for Materials Research, funded by the National Science Foundation (NSF), Paul McEuen, Dan Ralph, Hector Abruna and colleagues wedged a molecule containing a single cobalt atom between gold electrodes. They were able, using a gate voltage, to control the transfer of electrons across the cobalt atom, demonstrating the ability to regulate electrical flow at the smallest possible scale.
Hongkun Park and coworkers at Harvard University developed a transistor by inserting a different molecule containing two atoms of the metal vanadium between gold electrodes. The scientists were able to start and stop the flow of electrical current by adjusting the voltage near the bridging molecule, and observed magnetic interactions between electrons in the gold and the vanadium atom.
Park's research was supported by individual NSF grants and by the NSF Center for the Science of Nanoscale Systems and their Device Applications at Harvard. The di-vanadium molecule was developed by NSF grantee Jeffrey Long at the University of California at Berkeley.
By demonstrating the ability to control electron flow across one molecule and even a single atom, scientists have become optimistic about the ability to someday build the smallest possible electronic components. An important aspect of the research is developing the ability to conduct electrical measurements at the nanoscale; for example, to measure the electrical properties of single molecules. Both of the NSF-supported experiments demonstrated this ability.
For information on the materials center at Cornell, see: http://www.ccmr.cornell.edu/
For information on the nanoscience center at Harvard, see: http://www.nsec.harvard.edu/
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