Frizzed molecular carpets

Researchers have taken the first snapshots of heat bursts moving along hydrocarbon molecules.

A team led by Dana Dlott at the University of Illinois at Urbana-Champaign, anchored ends of the carbon-chain molecules to a gold surface, creating an atomic-scale carpet. A laser pulse then heated the gold base to around 800 kelvins in less than a trillionth of a second. Meanwhile, the team measured how the top of the carpet scattered light from a second laser. When heat reached the molecules’ upper ends, making them jiggle, the scattered signal changed.

By repeating the experiment on hydrocarbons of different lengths, the researchers showed that the bursts traveled along single molecules at a constant speed of about 1 kilometer per second. That’s much faster than heat diffuses in a macroscopic object. The findings appear in the Aug. 10 Science.

Understanding how molecules conduct heat will be crucial for “molecular electronics,” Dlott says. Researchers in that field seek circuits in which single electrons carry information down molecule-thin wires.

Arun Majumdar of the University of California, Berkeley says that this is “certainly an excellent piece of work.” Other experiments have suggested that heat’s speed is constant along a molecule and even faster than Dlott’s group measured. “I wonder what is going on,” Majumdar says.

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