Transistor strips: The researchers produced a number of graphene ribbons of varying thickness for the study. The thinner the ribbon, the more nitrogen bonded to its edges, affecting its electrical properties.
While it seems like a simple trick, Dai says that it yielded somewhat unexpected results. “What’s interesting is we didn’t find a decrease in [electron] mobility,” he says. This means that electrons were able to zip through the graphene at the same speeds as before, which is important since high electron mobility makes graphene an attractive material for future electronics.
The reason for this, Dai suspects, is that the edges of the graphene ribbons are more likely to bond to the nitrogen atoms than to atoms within the ribbon. This is an important insight, he says: it matches with the theory developed by his colleagues at the University of Florida, including Youngki Yoon and Jing Guo, which states that graphene ribbons can be doped–or chemically altered, as is the case with n- and p-type transistors–by bonding atoms to the edges, since the ribbons themselves are so narrow. This should make building electronic devices easier because it’s more challenging to control the doping of atoms within sheets of graphene.
Dai says that the new results lay the foundation for understanding the chemistry of graphene ribbons better, and for experimenting with atoms that can be used to dope graphene. But still, he says, researchers are a long way from producing graphene circuits that could compete with silicon. One of the main hurdles, he says, is that ribbons still can’t be manufactured in a completely uniform manner–something that’s required for a standardized manufacturing process.