"Researchers have wanted to make transistors out of carbon nanotubes but the problem is that they grow in all sorts of directions," said Brian Kiraly of Argonne. "The innovation here is that you can grow these along circuit paths that works for your tech."
UW researchers used chemical vapour deposition to grow graphene nanoribbons on germanium crystals. This technique passes a mixture of methane, hydrogen and argon gases into a tube furnace. At high temperatures, methane decomposes into carbon atoms that settle onto the germanium's surface to form a uniform graphene sheet. By adjusting the chamber's settings, the UW team was able to exert precise control over the material.
"What we've discovered is that when graphene grows on germanium, it naturally forms nanoribbons with these very smooth, armchair edges," said Michael Arnold, an associate professor of materials science and engineering at UW-Madison. "The widths can be very, very narrow and the lengths of the ribbons can be very long, so all the desirable features we want in graphene nanoribbons are happening automatically with this technique."
Using scanning tunnelling microscopy, a technique using electrons to see the characteristics of a sample, researchers confirmed the presence of graphene nanoribbons growing on the germanium. Data gathered from the electron signatures allowed the researchers to create images of the material's dimensions and orientation. In addition, they were able to determine its band structure and extent to which electrons scattered throughout the material.
"We're looking at fundamental physical properties to verify that it is, in fact, graphene and it shows some characteristic electronic properties," said Kiraly. "What's even more interesting is that these nanoribbons can be made to grow in certain directions on one side of the germanium crystal, but not the other two sides."
As their investigations continue, researchers can now focus their efforts on exactly why self-directed graphene nanoribbons grow on one face and determine if there is any unique interaction between the germanium and graphene that may play a role.
