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Penn Engineers Show How 'perfect' Materials Begin to Fail

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In this microscope image of the edge of a defect-free palladium nanowire, the array of dots represents single atomic columns.

Researchers at the University of Pennsyvlvania/Max Planck Institute for Intelligent systems stretched defect-free palladium nanowires to determine the cause of breakage.

Credit: Penn News

The cause of defect-free material breakage, which can cascade into failure, is described by a University of Pennsylvania/Max Planck Institute for Intelligent Systems project.

The researchers stretched defect-free palladium nanowires and found the stretching force at which they failed to be unpredictable, occurring in a range of values where ambient temperature wielded a much stronger influence than expected. The thermal uncertainty in the failure limit implies the point where a failure-inducing defect first manifests is on the wire's surface, where atoms exhibit more liquid-like behavior and their higher mobility makes their reconfiguration into the start of a line defect more probable.

"Our goal was to deduce the point where the first of the nanowire's atoms begin to shift out of their original positions and form a mobile defect," says University of Pennsylvania professor Daniel Gianola.

The researchers mapped out failure points by stretching the nanowires at various temperatures, confirming thermal activation. "When you make these really small structures, they're often grown from the bottom up...and that can give you a much more pristine structure than if you were to take a big block of metal and whittle it down," Gianola notes. "In addition, the atoms on the surface comprise a much larger proportion of the total and can control the properties of the nanoscale material."

From Penn News
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