Friday, December 11, 2009

Buckyballs and Nanotubes

A once overlooked form of carbon may represent the future of technology

Fullerenes, a form of solid carbon distinct from diamond and graphite, owe their discovery to a supersonic jet—but not of the airplane variety. At Rice University in 1985 the late Richard E. Smalley, Robert F. Curl and Harold W. Kroto (visiting from the University of Sussex in England), along with graduate students James R. Heath and Sean C. O’Brien, were studying carbon with a powerful tool that Smalley had helped pioneer: supersonic jet laser spectroscopy. In this analytical system, a laser vaporizes bits of a sample; the resulting gas, which consists of clusters of atoms in various sizes, is then cooled with helium and piped into an evacuated chamber as a jet. The clusters expand supersonically, which cools and stabilizes them for study.

In their experiments with graphite, the Rice team recorded an abundance of carbon clusters in which each contained the equivalent of 60 atoms. It puzzled them because they had no idea how 60 atoms could have arranged themselves so stably. They pondered the conundrum during two weeks of discussion, frequently over Mexican food, before hitting on the solution: one carbon atom must lie at each vertex of 12 pentagons and 20 hexagons arranged like the panels of a soccer ball. They named the molecule “buckminsterfullerene,” in tribute to Buckminster Fuller’s similar geodesic domes. Their discovery sparked research that led to elongated versions called carbon nanotubes, which Sumio Ijima of NEC described in a seminal 1991 paper. Both “buckyballs” and nanotubes could have been found earlier. In 1970 Eiji Osawa of Toyohashi University of Technology in Japan postulated that 60 carbon atoms could adopt a ball shape, but he did not actually make any. In 1952 two Russian researchers, L. V. Radushkevich and V. M. Lukyanovich, described producing nanoscale, tubular carbon filaments; published in Russian during the cold war, their paper received
little attention in the West.

As it turned out, buckminsterfullerene is not hard to make. It forms naturally in many combustion processes involving carbon (even candle burning), and traces can be found in soot. Since the Rice discovery, researchers have devised simpler ways to create buckyballs and nanotubes, such as by triggering an electrical arc between two graphite electrodes or passing a hydrocarbon gas over a metal catalyst. Carbon nanotubes have drawn much scrutiny; among their many intriguing properties, they have the greatest tensile strength of any material known, able to resist 100 times more strain than typical structural steel. During an interview with Scientific American in 1993, Smalley, who died in 2005 from leukemia, remarked that he was not especially interested in profiting from fullerenes. “What I want most,” he said, “is to see that x number of years down the road, some of these babies are off doing good things.” Considering that nanotubes in particular are driving advances in electronics, energy, medicine and materials, his wish will very likely come true.

Source of Information : Scientific American September 2009

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