09-27-00 14:44
No 55287
The future is now...
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. (Hla et al., Physical Review Letters, 25 Sept; Select Articles.)
http://www.aip.org/enews/physnews/2000/s
