From: J. R. Molloy (jr@shasta.com)
Date: Wed Sep 27 2000 - 18:46:19 MDT
Thanks to Andrew Ducker for the following.
SINGLE-MOLECULE STM CHEMISTRY. The versatility and exactitude of the scanning
tunneling microscope (STM) is demonstrated in a new experiment at the Free
University of Berlin, where scientists have for the first time manipulated
single molecules to perform a complete chemical reaction. Saw-Wai Hla
(011-49-30-838-52-813) and his colleagues start with several iodobenzene (C6H5I)
molecules resting on a terraced copper substrate. Then they dissociate some of
the molecules into iodine and phenyl (C6H5) by injecting electrons from the STM
tip. Next the iodine atoms are herded up and moved away with the STM tip. Now
the tip pulls one phenyl close to another; they are not yet chemically bonded,
though: pulling on one phenyl does not bring the other one along. Finally,
another splash of electrons from the tip effectively welds the two phenyls
together; proof that binding occurs is that when one phenyl is pulled with the
tip, the other comes along for the ride (see a drawing of this sequence at
Physics News Graphics.
In summary, the making of C12H10 molecules from C6H5I molecules, normally
carried out on a copper catalyst and using thermal activation (a process
chemists call the Ullmann reaction), has here been forced to proceed by
employing one molecule at a time at a cryogenic temperature of 20 K. The
researchers believe that new manmade molecules, never before seen in nature, can
be engineered in this way, including the selective detachment or replacement of
parts of larger molecules for individual assembling of molecular based
nano-devices.
http://www.aip.org/enews/physnews/2000/split/pnu503-2.htm
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