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Nanomaterials made through pressure

Using pressure instead of chemicals, a Sandia National Laboratories team has fabricated nanoparticles into nanowire-array structures like those that underlie the surfaces of touch screens for sensors, computers, phones and TVs.

The pressure-based process, called stress-induced fabrication, is said to take nanoseconds, whereas the chemistry-based industrial techniques take hours.

A new technology, the process mimics imprint processes already used by manufacturers. "Only instead of embossing credit cards, we're using the same type of process to fabricate nanowires or other nano-sized components at ultrashort time scales," said Sandia researcher Hongyou Fan.

According to the team, the method is 9 million times faster than any known chemical method when performed on Sandia’s pulsed-power machine, which generates pressures on the order of 100,000 atmospheres.

Embossing machines similar to those already commercially in use could potentially be used. "It's conceivable that few modifications would be needed to convert the machines from embossing to fabrication," Fan said.

The Sandia process saves on materials because exactly the amount needed is placed on a substrate.

Also, defects common in industrial chemical fabrication of semiconductors are reduced in number by the pressure process, which acts to fill any vacancies occurring in the product's atomic lattice.

"To produce the underlying nanowiring for a touch screen, the pressure has to be worked out beforehand to stop the compression at just the right distance from the target: not too far, not too close," said Fan. "It's a matter of programming the force applied to precisely determine how much to compress."

The nanowires therefore need to be made flexible enough to contact an electrically charged layer of the device when pressed by a finger, yet far enough apart to remain separate when there's no signal.

The technology can fabricate a variety of nanoscale components including nanorods and nanosheets. The method could be used for chemical sensors, strain detectors and electrodes in solar cells.

Peggy Lee

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