The original nanoworkout -- Helping carbon nanotubes get into shape

A carbon nanotube bundle before (left) and after (right) densification. Click here for more information.

Troy, N.Y. -- Researchers at Rensselaer Polytechnic Institute have developed a new method of compacting carbon nanotubes into dense bundles. These tightly packed bundles are efficient conductors and could one day replace copper as the primary interconnects used on computer chips and even hasten the transition to next-generation 3-D stacked chips.

Theoretical studies show that carbon nanotubes, if packed closely enough together, should be able to outperform copper as an electrical conductor. But because of the way carbon nanotubes are grown – in sparse nanoscale “forests” where carbon molecules compete for growth-inducing catalysts – scientists have been unable to successfully grow tightly packed bundles.

James Jiam-Qiang Lu, associate professor of physics and electrical engineering at Rensselaer, together with his research associate Zhengchun Liu, decided to investigate how to “densify” carbon nanotube bundles after they are already grown. He detailed the results of the post-growth densification project on June 6 at the Institute of Electrical and Electronics Engineers’ International Interconnect Technology Conference (IITC) in Burlingame, Calif.

Lu’s team discovered that by immersing vertically grown carbon nanotube bundles into a liquid organic solvent and allowing them to dry, the nanotubes pull close together into a dense bundle. Lu attributes the densification process to capillary coalescence, which is the same physical principle that allows moisture to move up a piece of tissue paper that is dipped into water.

The process boosts the density of these carbon nanotube bundles by five to 25 times. The higher the density, the better they can conduct electricity, Lu said. Several factors, including nanotube height, diameter, and spacing, affect the resulting density, Liu added. How the nanotubes are grown is also an important factor that impacts the resulting shape of the densified bundles.