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Posted on: 2/25/2010 12:00:00 AM... Jun Lou, an assistant professor in mechanical engineering and materials science at Rice University and TMS member, has discovered that gold wires between three-billionths and 10-billionths of a meter wide weld themselves together quite nicely—without heat. The discovery of these phenomena could be useful in development of high-density electronic devices, since heat-induced welds on the nanoscale run the risk of damaging the materials' strength or conductivity.

Lou and his group report that clean gold nanowires with identical atomic structures will merge into a single wire that loses none of its electrical and mechanical properties. The process works just as well with silver nanowires, which bond with each other or with gold. Jian Yu Huang, another TMS member and staff scientist at the Center for Integrated Nanotechnologies at Sandia National Laboratories, also worked on the project. Their findings are detailed in the article, “Cold Welding of Ultrathin Gold Nanowires,” published February 14 in Nature Nanotechnology.

Observing cold-welding phenomena on the nanoscale was actually not what the scientists were searching for or expecting. Instead, their experiment focused on determining the tensile strength of gold nanowires by attaching one end of a wire to a probe in a transmission electron microscope and the other to an atomic force microscopy probe.

Pulling the wire apart gave the team a measurement of its strength. What they didn't expect to see was the broken wire mending itself when its ends or sides touched. Measurements showed the reconnected wire was as strong as before.

In subsequent testing, Lou found the nanowires could be snapped and welded many times. Mended wires never broke again at the same spot, attesting to the strength of the new bond.

The wire's electrical properties also seemed unaffected by repeated breaking and welding. "We'd break a wire and reweld it 11 times and check the electrical properties every time. All the numbers were very close," Lou said in a February 15 Rice press release.

"There are a lot of surface atoms, very active, that participate in the diffusion at the nanoscale," Lou continued. "We tried gold and silver, and they weld in the same way as long as you satisfy the crystalline-orientation requirement."

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