A molecule has been designed to move in a straight line on a flat surface by closely mimicking human walking.

The molecule—9,10-dithioanthracene or “DTA”—has two linkers that act as feet. Obtaining its energy from heat supplied to it, the molecule moves such that only one of the linkers is lifted from the surface; the remaining linker guides the motion of the molecule and keeps it on course. Alternating the motions of its two “feet,” DTA is able to walk in a straight line without the assistance of nano-rails or nano-grooves for guidance.

“Similar to a human walking, where one foot is kept on the ground while the other moves forward and propels the body, our molecule always has one linker on the surface it is on, which prevents the molecule from stumbling to the side or veering off course,” said Bartels, assistant professor of chemistry and a member of UCR’s Center for Nanoscale Science and Engineering. “In tests, DTA took more than 10,000 steps without losing its balance once. Our work proves that molecules can be designed deliberately to perform certain dynamic tasks on surfaces.”

Bartels explained that, ordinarily, molecules move in every unpredictable direction when supplied with thermal energy. “DTA only moves along one line, however, and retains this property even if pushed or pulled aside with a fine probe.” Bartels said. “This offers an easy realization of a concept for molecular computing proposed by IBM in the 1990s, in which every number is encoded by the position of molecules along a line similar to an abacus, but about 10 million times smaller. IBM abandoned this concept, partly because there was no way to manufacture the bars of the abacus at molecule-sized spacing.

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