Here's some info on Nanotubes. Perhaps I was premature
in naming them Buckytubes. Nanotubes seems to be the
accepted name now.
Though, now they're making nanotubes with buckyballs inside
the tubes. Cool!
Scott
From Today's New York Times Science Section:
http://www.nytimes.com/2002/07/16/scien ... 6NANO.html
It Slices! It Dices! Nanotube Struts Its Stuff
By KENNETH CHANG
BOSTON - It is stronger than steel and far sharper than a pin. It shoots electrons and draws away heat. It can become the thinnest of wires and, potentially, electronic devices almost as minuscule as molecules.
In the last decade, the cylindrical molecule of carbon known as a nanotube has become a do-all wonder substance, touted for future use in everything from X-ray machines to paint. Nanotubes are already sprinkled in more than half of lithium ion batteries: their ability to carry electricity hastens recharging, and they act like tiny springs to hold apart the sheets of graphite in the battery, extending its lifetime.
More than 200 scientists attended a Nanotube 2002 conference here from July 6 to July 11 to learn about some of the latest news. Nanotubes glow in infrared light. They can be welded together. They can be used for fluorescent lights.
The reasons for nanotubes' remarkable properties are chemical and architectural.
In one form of carbon, the orbits of its outer electrons form three lobes that flare outward at 120-degree angles. Each lobe bonds with a lobe of a neighboring carbon atom, forming a honeycomb pattern that looks like a piece of chicken wire. The bonds between the carbon atoms are strong, stronger than those of diamond.
This flat chicken-wire configuration of carbon is well known; it's graphite, the stuff of pencil lead. But graphite sheets do not cling very strongly to one another, so a lump of it is soft and easily rubs off.
Just as a piece of paper is stronger when rolled up, graphite becomes extraordinarily stiff when the opposite edges of a rectangular sheet are connected, forming a cylinder.
That is a nanotube. "This is the strongest material that will ever be made," said Dr. David E. Luzzi, a professor of materials science at the University of Pennsylvania.
And very thin. The nanotube gets its name from nanometer, or a billionth of a meter, which is roughly the diameter of the thinnest of nanotubes.
The prospect of a strand that is long, strong and thin conjures dreams of epic engineering like spinning a 22,300-mile-long cable out of nanotubes to tether a satellite in orbit around the earth, and then building an elevator that goes from the ground floor literally into outer space.
The present reality is more modest. In May, researchers at Rensselaer Polytechnic Institute in Troy, N.Y., reported in the journal Science that they had produced the world's longest nanotubes - eight inches.
But scientists have already coaxed shorter nanotubes to line up and stick together into long strands.
At the conference, Dr. Philippe Poulin, a scientist at the National Center for Scientific Research in France, described how nanotubes could be dispersed into a liquid, mixed with polymers and spun into a fiber thinner than a human hair.
At present, the nanotube fiber is not as strong as some other artificial fibers like kevlar. But Dr. Poulin said he expected scientists to find ways to strengthen the bonds between individual nanotubes, perhaps by heating the fibers or dipping them in a chemical.
The fibers could also find use in tiny machines. Adding electrical charge expands the bonds between carbon atoms, lengthening the fiber by a small fraction. If the nanotube fiber is glued to a strip of another material that does not shrink or expand, the voltage causes the fiber to bend like an archer's bow. "You're making it a muscle," Dr. Poulin said.
Because of the strength of nanotubes, the fiber would exert 50 to 100 times as much force as a human muscle of the same size.
Many scientists also expect that nanotubes will be an important component in future molecular-scale electronic circuits.
Nanotubes vary in diameter and in how they are rolled up. If a nanotube is rolled evenly, like a sheet of paper with the top and bottom edges lined up, it is a metallic conductor, efficiently carrying electricity. Adding metallic nanotubes to plastic, for example, changes it from an insulator to a conductor - allowing an automaker, for instance, to use electrically charged paint that adheres better to conducting surfaces.
If a nanotube is twisted askew, like a misbuttoned shirt, then its electrical properties can change to those of a siliconlike semiconductor whose current can be switched on and off.
Researchers at I.B.M. have already built transistors with performance comparable to present-day silicon ones. (But the transistors are not particularly small, and I.B.M. has no idea how to mass-produce them.)
Scientists have also found they can further alter the electronic behavior of nanotubes by stuffing other molecules inside. In 1998, Dr. Luzzi discovered what looked like little balls within some of his nanotubes. The balls were buckyballs - also molecules of carbon, but in the shape of soccer balls. Dr. Luzzi called the stuffed tubes "pea pods."
Putting other atoms and molecules inside a nanotube could alter its electronic behavior in the same way that impurities are added to silicon for use in electronic devices. "Now we are working on ways we can tune its properties," Dr. Luzzi said.
Another trick is that when a voltage is applied along a nanotube, it shoots out electrons, like a cathode ray tube at the back of a television tube, but much, much smaller.
"We basically take the C.R.T. and flatten it by putting millions of electron guns instead of one gun," said Dr. Zvi Yaniv, president of SI Diamond Technology of Austin, Tex. SI Diamond has developed nanotube displays for lighted billboards like those in Times Square, but at a quarter of the cost of L.E.D.'s.
Samsung of Korea has also latched onto this idea and plans to begin selling large flat-panel televisions that are lighted by thin layers of nanotubes in late 2003.
In a variation on that theme, scientists at the University of North Carolina reported on July 8 in Applied Physics Letters that they had built a novel X-ray machine, using nanotubes to fire electrons at a piece of metal. The collisions produce X-rays, a higher energy form of light.
Nanotubes may also prove useful as sensors. Molecules that latch onto specific molecules - carbon monoxide, hydrocarbons or, more ambitiously, a piece of DNA - can be attached to the outside of a nanotube. Electric current runs along the surface of a nanotube, so when the sensor molecule snags its target, it redirects the current like a stone in a river.
What will limit the large-scale use of nanotubes in electronics in the near future is that current manufacturing techniques produce a clump of tubes of different diameters and different amounts of twist, or chirality. For some uses, like the fibers, the mixture of different types of nanotubes does not pose much of a problem. But metallic nanotubes short-circuit electronic devices and must be sifted out from the semiconducting ones.
"The holy grail would be to turn a knob and out comes the nanotube of the right diameter and chirality," said Dr. Mildred S. Dresselhaus, a professor of physics at the Massachusetts Institute of Technology. "We have yet to figure out how to do this."
That slows the research. "If you don't have material, you don't have an experiment," Dr. Dresselhaus said.
Nanotubes are also still very expensive; purified ones cost about $250,000 a pound.
Still, even in limited quantities, the molecule is providing moments of pure scientific surprise. Dr. Richard E. Smalley, a professor of chemistry at Rice University in Houston, and his colleagues are studying what colors of light are absorbed by single nanotubes, a technique known as spectroscopy that can tell details about a molecule's structure. They found that the nanotubes not only absorbed certain frequencies of infrared light, but also emitted them.
An undergraduate student at Rensselaer was surprised when a clump of nanotubes caught fire as he took a picture of it. The nanotubes had captured the energy from the camera flash and turned it into heat.
Besides its strength and electronic properties, a nanotube is also an excellent conductor of heat. Because it is so stiff, it vibrates at high frequencies like a taut guitar string - and heat is no more than the vibrations of atoms. Thus, for computer chips as envisioned by I.B.M., the nanotubes may not only do the calculating, but they could also help carry heat away and keep the chip from overheating.
This property of nanotubes allowed Dr. Morinobu Endo, a professor of engineering at Shinshu University in Japan, to make what he says are the world's smallest working gears. He mixed nanotubes into molten nylon and then squirted the nylon into a tiny mold. Instead of the outer skin cooling first, the heat-diffusing property of nanotubes kept the nylon uniformly molten as it filled every nook and cranny of the mold.
That produced a finely chiseled gear about as wide as a human hair. The nanotubes also give it strength. Coincidentally, they also conduct electricity, a superfluous capability for a gear. Sometimes some of nanotubes' amazing properties are more than needed.
