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September 16th, 2011

The thrill of victory and the agony of defeat: Some of each for CNTs

Published on September 16th, 2011 | By: Eileen De Guire

Rice University researchers, Robert Vajtai, Enrique Barrera and Yao Zhao created a conductive cable from iodine-doped nanotubes capable of carrying household current. Credit: Jeff Fitlow/Rice University

Showing how something works is more effective than telling how it works. With the assistance of a fluorescent lightbulb, Rice University researchers demonstrated successful substitution of standard copper wiring with a carbon nanotube cable.

Using double-walled CNTs spun into a cable several centimeters long, a recent Rice PhD, Yao Zhao, constructed a rig that allowed him to run electricity through a CNT cable to a fluorescent lightbulb. The lightbulb was left “on” for several days without interruption and without any sign of degradation in the CNT cable. Zhao is in Enrique Barrera’s research group. CTT recently interviewed Barrara as part of the MSE football series.

The cable was constructed of billions of double-wall CNTs and fabricated by collaborators at Tsinghua University in China. The cables were doped with iodine to increase their conductivity, and Zhao found they could be tied together without losing conductivity.

In a Rice press release, Barrera says the cables have the potential to be just as effective as metal wiring, at about 1/6 the weight. He also said that the chemical processes used to make lab-scale cables will become part of a larger process that starts with raw materials and produces a steady stream of nanocable. The next step for the team is “to make longer, thicker cables that carry higher current while keeping the wire ligtweight.”

The work was published in the Nature journal, Scientific Reports.

Meanwhile, NIST has been studying the reliability of CNTs for electronic devices with the goal of developing measurement and techniques to test fabrication quality and reliability.

of recession and clumping in gold electrodes after NIST researchers applied 1.7 volts of electricity to the carbon nanotube wiring for an hour. Credit: M. Strus; NIST

Recession and clumping, in gold electrodes after NIST researchers applied 1.7 volts of electricity to the carbon nanotube wiring for an hour. NIST reliability tests may help determine whether nanotubes can replace copper wiring in next-generation electronics.Credit: M. Strus; NIST

Possibly relevant to the Rice work, NIST researchers have been studying failure in CNT networks, where electrons physically jump from one CNT to another, and found that failure seemed to happen between nanotubes, which is the point of greatest resistance. In a press release, NIST postdoctoral researcher, Mark Strus said that by monitoring the initial starting resistance and stages of degradation, it was possible to predict whether the resistance would degrade gradually or sporadically. Gradual degradation is preferred because it allows for operational limits to be set for devices. NIST has developed some electrical stress tests “that link initial resistance to degradation rate, predictability of failure and total device lifetime. The test can be used to screen for proper fabrication and reliability of nanotube networks.”

Also from NIST, a study of CNT interconnects between gold electrodes found that the CNTs carried very high current densities for awhile, but degraded under constant current. By about 40 hours, the edges of the metal electrodes receded and clumped, leading to device failure. Further NIST research is focusing on the intersections between CNT and metals, as well as between different CNTs. In th press release Strus said, “The common link is that we really need to study the interfaces.”

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