Walking Molecules

A single molecule has been made to walk on two legs. Ludwig Bartels and his colleagues at the University of California at Riverside, guided by theorist Talat Rahman of Kansas State University, created a molecule -- called 9,10-dithioanthracene (DTA) -- with two "feet" configured in such a way that only one foot at a time can rest on the substrate.

Activated by heat or the nudge of a scanning tunneling microscope tip, DTA will pull up one foot, put down the other, and thus walk in a straight line across a flat surface. The planted foot not only supplies support but also keeps the body of the molecule from veering or stumbling off course.

In tests on a standard copper surface, such as the kind used to manufacture microchips, the molecule has taken 10,000 steps without faltering. According to Bartels (ludwig.bartels@ucr.edu, 951-827-2041), possible uses of an atomic-sized walker include guidance of molecular motion for molecule-based information storage or even computation.

DTA moves along a straight line as if placed onto railroad tracks without the need to fabricate any nano-tracks; the naturally occurring copper surface is sufficient. The researchers now aim at developing a DTA-based molecule that can convert thermal energy into directed motion like a molecular-sized ratchet.

Kwon et al., Physical Review Letters, upcoming article
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