Nanotubes are ubiquitous in the world of science. Although several methods for making them exist, little is known about how these techniques physically produce the hollow fibers of carbon molecules known as nanotubes, that is until now. A multinational team of scientists has discovered that multi-walled carbon nanotubes made by the pure carbon arc method are, in fact, carbon crystals that form inside drops of glass-coated liquid carbon. The research appears in the 11 February 2005, issue of the journal Science, published by the AAAS, the science society, the world’s largest general scientific organization.
Glassy drops of carbon coat the fibers that house nanotubes after their synthesis with a carbon arc.
Nanotubes coated with glassy drops of carbon poke through the surface of a column housing nanotubes.
One way to make nanotubes involves using a carbon arc to heat graphite to about 5,000 C. An electrical current is passed through the graphite in a chamber filled with helium gas. The result is a sooty deposit on one of the electrodes that contains columns filled with nanotubes. "We were doing research on the electrical transport properties of carbon nanotubes when we noticed that the nanotubes had these little beads that looked like liquid drops on them, said lead author Walt A. de Heer, physics professor at the Georgia Institute of Technology.
Much like archeologists studying artifacts to decipher what happened in centuries past, the research team began with the photos of the liquid-like beads coating the nanotube fibers and worked their way back to try to find out how they got there. "Just by looking at them we realized that this has something to do with liquid," said de Heer. "So we asked the question, if the beads were once liquid carbon and the nanotubes they are attached to are also carbon, why didn’t the liquid carbon dissolve the nanotube? The answer is that the liquid must have been a glass at a lower temperature than the nanotube."
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