Skip to Content

A Step toward Graphene Circuitry

A new way to change the electronic properties of graphene could lead to ultrafast circuits.

For the first time, researchers have shown a way to build electron-rich graphene transistors, a crucial electronic building block that could lead to tiny, ultrafast circuits.

Carbon ribbons: A graphene nanoribbon is shown in the center of this image under an atomic force microscope. Adding nitrogen to the nanoribbon creates an n-type transistor, an important building block in graphene circuitry.

Graphene is formed with carbon atoms linked together like nanoscopic chicken wire; the resulting atom-thick material has electronic properties that make it promising for use in future electronics. Although the researchers haven’t yet made a graphene circuit, they’ve demonstrated a way to control the amount of electron-rich molecules that are added to graphene to make so-called n-type transistors, a crucial electronic component.

In order to make a complex circuit, explains Stanford University chemistry professor Hongjie Dai, who led the work, engineers require transistors that are both electron rich (n-type) and electron poor (p-type). Previously, researchers had only demonstrated p-type graphene transistors, which are easier to make than n-type transistors because oxygen atoms readily bond to the edges of graphene ribbons producing “holes,” electrons’ positively charged counterparts. With both n- and p-types of graphene transistors, it will be possible to build complex circuitry, says Dai. His team collaborated with Jing Guo’s group at the University of Florida and Peter Weber at Lawrence Livermore National Laboratory to develop the n-type graphene transistors. The work appears in the latest issue of Science.

Dai’s group is at the forefront of much of the cutting-edge work involving graphene. Last year, they demonstrated the first graphene nanoribbons–strips of graphene that range in width from about 10 nanometers to 150 nanometers; they also showed how to make p-type transistors with these nanoribbons. And in research published in Nature last month, Dai demonstrated a method of mass-producing graphene nanoribbons.

To make the n-type graphene, the researchers exposed nanoribbons, which were deposited on a wafer of silicon and silicon dioxide, to ammonia and high heat, explains Dai. “We found that if you heat up these ribbons in ammonia, then you can actually get nitrogen into the ribbons, and nitrogen donates electrons to the graphene.”

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.

Keep Reading

Most Popular

conceptual illustration showing various women's faces being scanned
conceptual illustration showing various women's faces being scanned

A horrifying new AI app swaps women into porn videos with a click

Deepfake researchers have long feared the day this would arrive.

2021 tech fails concept
2021 tech fails concept

The worst technology of 2021

Face filters, billionaires in space, and home-buying algorithms that overpay all made our annual list of technology gone wrong.

glacier near Brown Station
glacier near Brown Station

The radical intervention that might save the “doomsday” glacier

Researchers are exploring whether building massive berms or unfurling underwater curtains could hold back the warm waters degrading ice sheets.

Professor Gang Chen of MIT
Professor Gang Chen of MIT

In a further blow to the China Initiative, prosecutors move to dismiss a high-profile case

MIT professor Gang Chen was one of the most prominent scientists charged under the China Initiative, a Justice Department effort meant to counter economic espionage and national security threats.

Stay connected

Illustration by Rose WongIllustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at customer-service@technologyreview.com with a list of newsletters you’d like to receive.