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September 27, 2005 - Volume 83, Number 40
SURFACE DYNAMICS
Molecules Take A Walk
Unidirectional motion gives researchers control important for molecular machines, self-assembly
Elizabeth K. Wilson
Scientists have designed a molecule that “walks” across a surface in a straight line, putting one bond in front of the other. Such purposeful control of a molecule’s motion is vital for advancing fields such as molecular self-assembly, molecular machines, and computing.
View a video of the "walking" molecule in Quicktime format (6.2MB)--COURTESY OF LUDWIG BARTELS
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STROLLER 9,10-Dithioanthracene walks a straight line along a copper surface. |
The electrically charged tip of a scanning tunneling microscope serves as a sort of carrot, luring a single 9,10-dithioanthracene molecule across a copper surface. A thermal vibration can also act as a lure. The researchers—Ludwig Bartels, assistant professor of physical chemistry and chemical physics at the University of California, Riverside, graduate student Ki-Young Kwon, and colleagues there and at Kansas State University—report their findings in an upcoming issue of Physical Review Letters.
The molecule toddles over the copper atoms on thiol linker “legs”: As the “body” of the molecule pivots forward, one leg bonds to the surface while the other detaches. The group performed density functional theory calculations to help confirm the walking motion.
Flemming Besenbacher, head of the Interdisciplinary Nanoscience Center for the University of Aarhus and Aalborg University, both in Denmark, calls the study “a nice piece of work,” but notes that a number of researchers have explored one-dimensional diffusion of molecules on a surface (Nat. Mater. 2004, 3, 779). Those studies, however, have generally used surfaces with step edges or anisotropic surfaces, which help keep the molecule moving in one direction. The new research was done on an isotropic surface, where all directions look the same to the molecule.
The Bartels group’s work adds to the already fertile field of manipulating and probing molecules on surfaces, says Robert J. Celotta, a physicist at the National Institute of Standards &Technology in Gaithersburg, Md., who recently studied the guided motion of a single cobalt atom across a copper surface (Science 2004, 306, 242). “It represents a beautiful demonstration of the use of [these methods] to understand a very basic form of molecular locomotion.”
- Chemical & Engineering News
- ISSN 0009-2347
- Copyright © 2006 American Chemical Society
