by Andrew Myers
Stanford CA (SPX) Feb 09, 2012
One area of intensive research at the nanoscale is the creation of electrically conductive meshes made of metal nanowires. Promising exceptional electrical throughput, low cost and easy processing, engineers foresee a day when such meshes are common in new generations of touch-screens, video displays, light-emitting diodes and thin-film solar cells.
Standing in the way, however, is a major engineering hurdle: 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.
In a paper just published in the journal Nature Materials, a team of engineers at Stanford has demonstrated a promising new nanowire welding technique that harnesses plasmonics to fuse the wires with a simple blast of light.
"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 at Stanford and an expert in plasmonics. Brongersma is one of the study's senior authors.
"The rest of the wires and, just as importantly, the underlying material are unaffected," noted Michael McGehee, a materials engineer and also senior author of the paper. "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.
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.
"Then we balled it up like a piece of paper. When we unfurled the wrap, it maintained its electrical properties," said co-author Yi Cui, an associate professor materials science and engineering. "And when you hold it up, it's virtually transparent."
This could lead to inexpensive window coatings that generate solar power while reducing glare for those inside, the researchers said.
"In previous welding techniques that used a hotplate, this would never have been possible," said lead author, Erik C. Garnett, PhD, a post-doctoral scholar in materials science who works with Brongersma, McGehee and Cui. "The Saran wrap would have melted far sooner than the silver, destroying the device instantly."
"There are many possible applications that would not even be possible in older annealing techniques," said Brongersma. "This opens some interesting, simple and large-area processing schemes for electronic devices - solar, LEDs and touch-screen displays, especially."
This research was supported by the Center for Advanced Molecular Photovoltaics (CAMP) at Stanford University funded by King Abdullah University of Science and Technology (KAUST).
Nano Technology News From SpaceMart.com
Computer Chip Architecture, Technology and Manufacture
Comment on this article via your Facebook, Yahoo, AOL, Hotmail login.
Nanorod-Assembled Order Affects Diffusion Rate and Direction
Atlanta GA (SPX) Feb 09, 2012
Some of the recent advancements in nanotechnology depend critically on how nanoparticles move and diffuse on a surface or in a fluid under non-ideal to extreme conditions. Georgia Tech has a team of researchers dedicated to advancing this frontier. Rigoberto Hernandez, a professor in the School of Chemistry and Biochemistry, investigates these relationships by studying three-dimensional pa ... read more