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Stanford University

Researchers at Stanford University have discovered a way to weld metal nanowires together using nothing but relatively ordinary light. They found that by placing one nanowire touching another, then shining a light on them, creates waves of light, also called plasmon waves. These waves create hot spots wherever the nanowires touch. The hot spot fuses the two metal wires together. This action also eliminates the hot spot as the plasmon waves now treat the two wires as one. So the welding is selflimiting and stops itself.

The light used was unpolarized, broadband illumination from 21 tungsten halogen lamps with a color temperature of 3,050 K. The lamps generated an illumination power density of about 30 W/cm2.

Nearby nanowires that did not overlap did not weld together, nor was the material the wires were laying on affected. The new technique could lead to new ways to make nanowire meshes bound to flexible and transparent polymers and plastics. To test that theory, researchers sprayed a solution containing silver nanowires onto a sheet of Saran Wrap. After shining the lamps on treated Saran Wrap, the engineers ended up with a thin web of welded nanowires connected to the flexible Saran Wrap. They crumpled then unfurled the plastic sheet, and found that the web maintained its electrical properties. In other words, the wires and connections were flexible. The engineers note that trying to replicate the effect using heat to weld the wires would have melted the Saran Wrap before the wires were fused.

Researchers predict this technique for building meshes could lead to window coatings that generate electricity from solar radiation while reducing glare inside. It could also lead to lowcost, largescale techniques for nanowiring LEDs, solar cells, ICs, and touchscreen displays.

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