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Nanowires welded into a mesh, using light

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February 7, 2012

One of the nanowire meshes, created by the Stanford scientists

One of the nanowire meshes, created by the Stanford scientists

Some day, meshes made from nanowires could be used in devices such as video displays, LEDs, thin-film solar cells, and touch-screens. According to research performed so far, such meshes would be very electrically conductive, cost-effective, and easy to process. What has proven challenging, however, is finding a way of getting the criss-crossed nanowires to fuse together to form that mesh - if pressed or heated, the wires can be damaged. Now, engineers from Stanford University may have found the answer ... just apply light.

The process utilizes plasmons, particles of oscillating plasma that are created when light strikes a metal surface - under the right conditions. When the Stanford team laid nanowires out on a metal platform, then subsequently illuminated it, plasmon activity was concentrated where the wires crossed one another.

"When two nanowires lay crisscrossed, we know that light will generate plasmon waves at the place where the two nanowires meet, creating a hot spot," explained Mark Brongersma, an associate professor of materials science engineering. "The beauty is that the hot spots exist only when the nanowires touch, not after they have fused. The welding stops itself. It's self-limiting."

Each top nanowire acted like an antenna, guiding the plasmon waves into the wire beneath it. This created heat, which caused the two nanowires to fuse together where they touched. The process didn't affect the rest of the wires, however, nor the underlying material.

Not only could this method be used to easily produce nanowire meshes, but it could also come in handy for creating mesh electrodes for use on flexible or transparent surfaces. To demonstrate this, the scientists sprayed a solution containing silver nanowires in suspension onto a piece of Saran Wrap, then allowed it to dry. After illuminating the surface, they were left with an ultrathin layer of welded nanowires. They then balled the plastic up like a piece of paper. When they smoothed it back out, the mesh maintained its electrical properties, and the coated plastic was still virtually transparent. The researchers believe that the technology could be used to apply inexpensive solar power-generating coatings to windows, that would still allow light to come through while reducing glare for people inside buildings.

According to Brongersma's colleague Dr. Erik C. Garnett, previous nanowire-welding techniques would have melted the Saran Wrap before affecting the silver nanowires.

A paper on the research was recently published in the journal Nature Materials.

Source: Stanford University

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away.   All articles by Ben Coxworth
1 Comment

Dang if this isn't one of the cleverest little things I've read on this site. But what strikes me is, the image in the above story - it is of stuff created at a nano-scale, and yet the image is as clear as if it were a photo of spaghetti. The depth of detail and grain still left to nature to tell it's tale, even at the nano-scale, is so wide that a photo of nano wires is of small consequence. Just for a second, you have a sense of how small things could yet get...

Chris Clarke
16th February, 2012 @ 03:24 am PST
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