Welded nanowires may lead to low-cost touch-screens, video displays, LEDs, and thin-film solar cells

February 7, 2012

Scanning electron microscope image of plasmonically welded silver nanowires (credit: Mark Brongersma/Stanford University)

Stanford University engineers have demonstrated a promising new nanowire welding technique to create electrically conductive meshes made of metal nanowires.

The research promises to lead to exceptional electrical throughput, low cost and easy processing for new generations of touch-screens, video displays, light-emitting diodes, and thin-film solar cells.

In processing, these delicate meshes must be heated or pressed to unite the crisscross pattern of nanowires that form the mesh, damaging them in the process.

The solution is to use plasmonics, the interaction of light and metal in which the light flows across the surface of the metal in waves.

“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. The beauty is that the hot spots exist only when the nanowires initially touch, not after they have fused. The welding stops itself. It’s self-limiting,” explained Mark Brongersma, an associate professor of materials science engineering at Stanford.

“This ability to heat with precision greatly increases the control, speed and energy efficiency of nanoscale welding.”

In before-and-after electron-microscope images, individual nanowires are visually distinct prior to illumination. They lay atop one another, like fallen trees in the forest. When illuminated, the top nanowire acts like an antenna of sorts, directing the plasmon waves of light into the bottom wire and creating heat that welds the wires together. Post-illumination images show X-like nanowires lying flat against the substrate with fused joints.

In addition to making it easier to produce stronger and better performing nanowire meshes, the researchers say that the new technique could open the possibility of mesh electrodes bound to flexible or transparent plastics and polymers.

To demonstrate the possibilities, they applied their mesh on Saran wrap. They sprayed a solution containing silver nanowires in suspension on the plastic and dried it. After illumination, what was left was an ultrathin layer of welded nanowires.

This could lead to inexpensive window coatings that generate solar power while reducing glare for those inside, the researchers said.

Ref.: Erik C. Garnett, et al., Self-limited plasmonic welding of silver nanowire junctions, Nature Materials, 2012; [DOI:10.1038/nmat3238]