Researchers figure out how to grow uniform batches of carbon nanotubes

Carbon nanotubes, tiny tubes of rolled up graphene that measure just 1 nanometer across, are super-strong structures that could someday be used in solar cells, batteries, electronic circuits and everyday objects. While researchers are getting better at making large batches of carbon nanotubes, producing them uniformly has been elusive.

University of Southern California researchers published a paper August 23 that details how to reliably grow specific types of carbon nanotubes. Generally, they are made in batches that contain lots of differently shaped nanotubes, which are then sorted. Sorting increases costs and shortens the length to which nanotubes can be grown.

“To be able to control the atomic structure, or chirality, of nanotubes has basically been our dream, a dream in the nanotube field,” USC electrical engineering professor Chongwu Zhou said in a release. “We are now working on scaling up the process.”

Carbon nanotubes are made of hexagons of carbon atoms bonded together. Minute changes in the orientation of the hexagons is enough to change the properties of a carbon nanotube, such as if it is a semiconductor or not.

Carbon nanotube chirality

To grow the specific types, the researchers started with short pieces of pre-sorted nanotubes. The nanotubes were exposed to carbon-containing gas at a high temperature, causing some carbon atoms to leave the air and extend the length of the tubes. The researchers first documented the technique last year, and now were able to pinpoint exactly how the unique structures grow. They noticed each type grows differently, including faster or longer under specific conditions.

Carbon nanotubes can be unzipped and flattened, leading he USC researchers to believe their growth technique could be used to create uniform batches of graphene as well.