Green Design

Welding Nanowires With Light

Electrically conductive meshes made of metal nanowires promise exceptional electrical throughput, low cost, and easy processing in applications like video displays, LEDs, and thin-film solar cells. However, in processing, these meshes must be heated or pressed to unite the crisscross pattern of nanowires that form the mesh - damaging them in the process.

A team of engineers at Stanford has demonstrated a new nanowire welding technique that harnesses plasmonics - the interaction of light and metal in which the light flows across the surface of the metal in waves - to fuse the wires.

“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 touch, not after they have fused. The welding stops itself. It’s self-limiting,” explained Mark Brongersma, an associate professor of materials science engineering.

In before-and-after electron-microscope images, individual nanowires are visually distinct prior to illumination. They lay atop one another. 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.