Molecule Walks Like A Human -- Potential Applications In Molecular Computing

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 suchthat only one of the linkers is lifted from the surface; the remaininglinker guides the motion of the molecule and keeps it on course.Alternating the motions of its two “feet,” DTA is able to walk in astraight line without the assistance of nano-rails or nano-grooves forguidance.

The researchers will publish their work in next month’s issue of Physical Review Letters.

“Similarto a human walking, where one foot is kept on the ground while theother moves forward and propels the body, our molecule always has onelinker on a flat surface, which prevents the molecule from stumbling tothe side or veering off course,” said Bartels, assistant professor ofchemistry and a member of UCR’s Center for Nanoscale Science andEngineering. “In tests, DTA took more than 10,000 steps without losingits balance once. Our work proves that molecules can be designeddeliberately to perform certain dynamic tasks on surfaces.”

Bartelsexplained that, ordinarily, molecules move in every unpredictabledirection when supplied with thermal energy. “DTA only moves along oneline, however, and retains this property even if pushed or pulled asidewith a fine probe.” Bartels said. “This offers an easy realization of aconcept for molecular computing proposed by IBM in the 1990s, in whichevery number is encoded by the position of molecules along a linesimilar to an abacus, but about 10 million times smaller. IBM abandonedthis concept, partly because there was no way to manufacture the barsof the abacus at molecule-sized spacing.

“DTA does not need anybars to move in a straight line and, hence, would allow a much simplerway of creating such molecular memory, which would be more than 1000times more compact than current devices.”

The UCR research teamis now trying to build a molecular ratchet, which would convert randomthermal oscillation into directed motion. “It would be similar to anautomatic watch that rewinds itself on the arm of the bearer – exceptthat it would be just one nanometer in diameter,” Bartels said.

Ananometer is one billionth of a meter. A nanometer is to a meter whatan inch is to 15,783 miles, more than half the distance around theEarth’s equator.

Bartels was assisted in the study by Ki-YoungKwon, Kin L. Wong and Greg Pawin of UCR; and Sergey Stolbov and TalatS. Rahman of Kansas State University. The US Department of Energyfunded the research. Additional support came from the PetroleumResearch Fund and the Air Force Office of Scientific Research. The SanDiego Supercomputer Center provided computational resources.