Silicon's successor lurks in the lab
Published: 20 Oct 2003 16:05 BST
The bonds that bind
Bonding is another key property that makes nanotubes attractive. Carbon atoms bond tightly to each other and gravitate toward the stable, hexagonal rings. Nanotubes "heal" themselves by shifting to replace atoms that get removed.
"Silicon is very finicky about defects," said David Tomanek, a professor of physics at Michigan State University. "We have concluded that carbon nanotubes are relatively defect-tolerant."
That has the potential to relieve huge headaches. Chipmaking facilities cost $3bn today and will likely cost $6bn by 2007. The lion's share of those funds goes toward equipment that's needed to draw circuits.
Self-assembling, correcting tubes eliminate the need for many of these machines. Most of the equipment required "is all pretty standard chemical industry stuff," Pitstick said.
Other applications benefit from bonding as well. Single-walled nanotubes, which are incredibly resilient to physical twisting or pulling, can be kinked to a 120-degree angle and bounce back to original form undamaged, said Hongjie Dai, an associate professor of chemistry at Stanford.
They can be long, too. Researchers have created defect-free nanotubes as long as four microns, which is 40 times the length of the average size of features on regular silicon chips. Some nanotubes with less-than-perfect ballistic features have been made as long as 120 microns.
Hypothetically, this could allow engineers to replace wires in airplanes with tubes, strengthening parts while reducing weight.
Carbon is also good for exploiting van der Waals forces, which cause different types of atoms to bond spontaneously. In experiments, researchers have noted that nanotubes will adhere to silicon posts that stick up from a wafer. As a result, they can be arranged in a useful array. Nantero, a start-up that had its beginnings at Harvard University, is aiming to exploit van der Waals forces to make a new type of memory chip.
"You get a wafer of tubes with a reasonable orientation," Dai said. "They really like to land on the post to enjoy the van der Waals contact."
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your efforts are appriciated to provide thew usefu... Moazzam Ali Kausar
