Unzipping Graphene's Potential

Continued from page 1

The two papers "show there is a path to create graphene from nanotubes," says Yu-Ming Lin, a researcher in the nanoscale science and technology group at IBM's Watson Research Center, in New York. Dai developed the previous standard for making graphene nanoribbons: breaking graphene sheets into smaller pieces, including nanoribbons, by exposing them to intense sound waves (a relatively low-yield method). "There are pros and cons for each [new] method," says Dai.

Tour's unzipping method yields graphene in bulk, which is an advantage from a manufacturing perspective. But "[Dai]'s going to have better control," admits Tour. The width of the Rice group's nanoribbons is determined by the diameter of the nanotubes that they come from. In contrast, using the Stanford team's technique, it's possible to finely control the width of the nanoribbons. In today's publication, Dai and his colleagues describe nanoribbons six nanometers wide, but he says that they have subsequently made narrower and more semiconducting ones. "There might be an optimum width; that needs to be investigated," he says.

Tour's nanoribbons are easy to process because they are graphene oxide, which is soluble in water. "You can use shear force to align them like logs in a river lining up in parallel," says Tour. "You can paint them down, and they will align." Tour adds that the nanoribbons can be made into devices using ink-jet printing. Once the ribbons are in place on a chip, they're treated with hydrogen at high heat to remove the oxygen at their edges and turn them into semiconductors. Without this step, the ribbons are insulators.

The Stanford research was funded by Intel, and Tour says that he is in talks with companies interested in licensing his manufacturing method as well as devices made with the nanoribbons.