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Source: "Low Temperature Synthesis of Vertically Aligned Carbon Nanotubes with Electrical Contact to Metallic Substrates Enabled by Thermal Decomposition of the Carbon Feedstock," Gilbert Nessim, Carl V. Thompson et al, Nano Letters, Aug. 31, 2009

Results: Researchers in the lab of MIT materials science professor Carl V. Thompson grew dense forests of crystalline carbon nanotubes on a metal surface at temperatures close to those characteristic of computer chip manufacturing. Unlike previous attempts to do the same thing, the researchers' technique relies entirely on processes already common in the semiconductor industry. The researchers also showed that the crucial step in their procedure was to preheat the hydrocarbon gas from which the nanotubes form, before exposing the metal surface to it.

Why it matters: The transistors in computer chips are traditionally connected by tiny copper wires. But as chip circuitry shrinks and the wires become thinner, their conductivity suffers and they become more likely to fail. A simple enough manufacturing process could enable carbon nanotubes to replace the vertical wires in chips, permitting denser packing of circuits.

How they did it: In a vacuum chamber, the researchers vaporized the metals tantalum and iron, which settled in layers on a silicon wafer. Then they placed the coated wafer at one end of a quartz tube, which was inserted into a furnace. At the wafer's end of the tube, the furnace temperature was 475 degrees C; but at the opposite end, the temperature varied. The researchers pumped ethylene gas into the tube from the end opposite the wafer. When the temperature at that end approached 800 degrees, the ethylene decomposed, and the iron on the wafer catalyzed the formation of carbon nanotubes.

Next steps: The researchers are trying to determine whether different combinations of metals and hydrocarbon gases can lower the catalytic temperature even further and improve the quality of the nanotubes.

Funding: The research was sponsored by the MARCO Interconnect Focus Center and partially by Intel (Gilbert Nessim, who was a graduate student in Thompson's lab, was supported by an Intel Fellowship).

About The Researcher :

Carl V. Thompson

Stavros Salapatas Professor of Materials Science and Engineering

Professor Thompson received his SB in Materials Science and Engineering from the Massachusetts Institute of Technology in l976. He received his SM and PhD degrees in applied physics from Harvard University in 1977 and 1982 respectively. He was an IBM postdoctoral fellow in the Research Laboratory of Electronics at MIT in l982 and joined the faculty of the Department of Materials Science and Engineering in l983. He received an IBM faculty development award in l983 and was appointed the Mitsui career development assistant professor of contemporary technology in l984 and l985. In 1987 he was appointed associate professor of electronic materials, and became a full professor in 1992. He is currently the Stavros Salapatas Professor of Materials Science & Engineering and Director of the Materials Processing Center

Professor Thompson spent the 1990-91 academic year at the University of Cambridge Department of Materials Science and Metallurgy, where he was awarded a United Kingdom Science and Engineering Research Council Visiting Fellowship. He spent the 1997-98 academic year at the Max-Plank Institute fur Metallforschung in Stuttgart and received a research award for Senior U.S. Scientist from the Alexander Von Humboldt Foundation. Professor Thompson's research is carried out in affiliation with the MIT Microsystems Technology Laboratory and the MIT Materials Processing Center, as well as the Department of Materials Science and Engineering. In 1999, Prof. Thompson was named an SMA Fellow in the Singapore-MIT Alliance Program and Co-Chairs the SMA program in Advanced Materials for Micro and Nano-Systems.

Professor Thompson has served on the Materials Research Society (MRS) Council, was the second Vice-President in 1994, the first Vice-President in 1995, and the President in 1996. He continues to serve on several committees and has organized a number of MRS symposia. He co-chaired the Spring 1991 MRS meeting.

Professor Thompson worked briefly for U.S. Steel and General Electric and has been a consultant for a number of microelectronics companies, new companies exploiting nanotechnology, and legal firms. Professor Thompson has also taught short courses at a number of companies, including Hewlett-Packard, Chartered Semiconductor, and Digital Equipment Corporation.