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Molecule gears up

Researchers construct a tiny version of the most basic component of a machine.

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4:13pm, June 22, 2009
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A single snowflake-shaped molecule atop a gold sheet can turn like a gear. By building this most basic component of a machine, researchers reporting in an upcoming Nature Materials have created a building block for complex miniature devices.

“This is another cog in the wheel for the development of molecular machines,” says James Tour, a chemist at Rice University in Houston.

Carlos Manzano of the Institute of Materials Research and Engineering in Singapore and his colleagues built the gear out of hexa-t-butyl-pyrimidopentaphenylbenzene, which has a central core with six rings jutting out and is only nanometers wide. One of the six rings differs slightly from the others, allowing the team to track the molecule’s rotation.

With the ultrafine tip of a scanning tunneling microscope, Manzano and his team were able to slide the molecules across a sheet of gold. But to turn the molecule into a gear, the researchers wanted to pin it firmly in place so that they could reliably rotate it.

Atom-sized impurities in the gold sheet (the exact nature of which are still mysterious) proved to be a good place to stick a molecule, Manzano says. When a molecule was centered on a tiny bump, a nudge with the scanning tunneling microscope would send the legs of the molecule gently rotating, while the center stayed stationary. Other axes, including a gold atom, did not work as well. When nudged, a molecule atop a gold atom shifted until the gold atom was stuck between two legs, creating a molecular tangle.

Controllable turning may eventually allow the transfer of motion between different tiny parts, opening the door for tiny machines. “What we have done here is to build and control a basic component, but at an infinitesimally smaller scale,” Manzano says.

Different kinds of molecules that change shape in response to signals may one day set gears turning without a scanning tunneling microscope’s poke. Charlie Sykes, a surface scientist at Tufts University in Medford, Mass., says, “In the future, it would be neat to use electricity or light to get motion.” Arrays of billions of gears linked up could be used to make new kinds of materials that could transmit motion across space, he says.

Tiny machines that can do work are still a long way off. Researchers must still figure out how to make one gear turn another gear without getting stuck, a problem that Manzano and his colleagues encountered with their molecule. “At the moment, we are still very far away from seeing any possible applications that could be called a molecule machine,” Manzano says.

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