12-01 :: January 2012
nanotimes News in Brief
61
In before-and-after electron-microscope images, indi- vidual nanowires are visually distinct prior to illumi- nation. 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 resear- chers 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 con- taining 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 pro- perties,” 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 hot- plate, this would never have been possible,” said lead author, Erik C. Garnett, PhD, a post-doctoral scholar in materials science who works with Bron- gersma, 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.”
Erik C. Garnett, Wenshan Cai, Judy J. Cha, Fakhruddin Mahmood, Stephen T. Connor, M. Greyson Christoforo, Yi Cui, Michael D. McGehee, Mark L. Brongersma: Self- limited plasmonic welding of silver nanowire junctions, In: Nature Materials AOP, February 05, 2012, DOI:10.1038/ nmat3238:
http://dx.doi.org/10.1038/nmat3238 http://engineering.stanford.edu/