Ghostly nano 'kites' may lead to holy grail of nanotube growth

Researchers at Houston’s Rice University have developed a method for making bundles of single-walled carbon nanotubes (SWNT) dubbed “odako”. Eventually, the method may realize meter-long strands of nanotubes that are no wider than a piece of DNA which could be used in lightweight, super-efficient power-transmission lines, in ultra-strong and lightning-resistant materials for airplanes, and may also prove useful in batteries, fuel cells and microelectronics.

The “odako” bundles feature many lines trailing from them so take their name from the gigantic traditional Japanese kites they resemble that take many hands to fly. In this case the lines are hollow cylinders of pure carbon that are individually many times smaller than a living cell. The method of producing them developed by the team at Rice University creates bundles of SWNT that are sometimes measured in centimeters and could eventually yield tubes of unlimited length.

The process starts with the printing process the U.S. Treasury uses to embed paper money with unique markings that make currency difficult to counterfeit to create thin layers of iron and aluminum oxide on a Mylar roll. They then removed the layers and ground them into small flakes. These metallic flakes were then placed in furnace inside a mesh cage where they 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.

While other methods used to grow SWNTs had yielded a paltry 0.5 percent ratio of nanotubes to substrate materials, the new technique brought the yield up to an incredible 400 percent offering the hope of large-scale SWNT growth.

In the latest research, the team replaced the Mylar with pure carbon, which resulted in the growing nanotubes literally lifting up the iron and aluminum oxide from which they’re sprouting while the other ends stay firmly attached to the carbon. As the bundle of tubes grows higher, the catalyst becomes like a kite, flying in the hydrogen and acetylene breeze that flows through the production chamber.

The research team hope their work will lead to the holy grail of nanotube growth: a catalyst that will not die, enabling furnaces that churn out continuous threads of material. “If we could get these growing so they never stop – so that, at some point, you pull one end out of the furnace while the other end is still inside growing – then you should be able to grow meter-long material and start weaving it,” said Rice University chemist Bob Hauge.

The Rice University research team’s findings appear in the papers, “Odako growth of dense arrays of single-walled carbon nanotubes attached to carbon surfaces”, “Synthesis of High Aspect-Ratio Carbon Nanotube 'Flying Carpets' from Nanostructured Flake Substrates” and "Role of Water in Super Growth of Single-Walled Carbon Nanotube Carpet.”