photo: nanotubes
An odako shows single-walled
nanotubes lifting an iron and
aluminum oxide "kite"; © Rice

Bob Hauge, a distinguished faculty fellow in chemistry at Rice University's Richard E. Smalley Institute for Nanoscale Science and Technology, and his colleagues explained the odako after which the bundles are named are gigantic kites that take many hands to fly, hence the many lines that trail from them.

In this case, the lines are nanotubes, hollow cylinders of pure carbon. Individually, they're thousands of times smaller than a living cell, but Hauge's new method creates bundles of SWNTs that are sometimes measured in centimeters, and he said the process could eventually yield tubes of unlimited length.

Large-scale production of nanotube threads and cables would be a godsend for engineers in almost every field. They could be used in ultra-strong and lightning-resistant versions of carbon-fiber materials. Hauge said the SWNT bundles may also prove useful in batteries and microelectronics.

Last year, the researchers found they could make compact bundles of nanotubes starting with the same machinery the U.S. Treasury uses to embed paper money with unique markings that make the currency difficult to counterfeit.

Hauge and his team used this printing process to create thin layers of iron and aluminum oxide on a Mylar roll. They then removed the layers and ground them into small flakes.

Here's where the process took off. In a mesh cage placed into a furnace, the metallic flakes would lift off and "fly" in a flowing chemical vapor. As they flew, arrays of nanotubes grew vertically from the iron particles in tight, forest-like formations. When done cooking and viewed under a microscope, the bundles looked remarkably like the pile of a carpet.

While other methods used to grow SWNTs had yielded a paltry 0.5 percent ratio of nanotubes to substrate materials, Hauge's technique brought the yield up to 400 percent. The process could facilitate large-scale SWNT growth.; Source: Rice University