Electronic properties of two layers of graphene vary on the nanometer scale
Researchers at the National Institute of Standards and Technology (NIST) have shown that the electronic properties of two layers of graphene vary on the nanometer scale. The surprising new results reveal that not only does the difference in the strength of the electric charges between the two layers vary across the layers, but they also actually reverse in sign to create randomly distributed puddles of alternating positive and negative charges. Reported in Nature Physics,* the new measurements bring graphene a step closer to being used in practical electronic devices.
Graphene, a single layer of carbon atoms, is prized for its remarkable properties, not the least of which is the way it conducts electrons at high speed. However, the lack of what physicists call a band gap—an energetic threshold that makes it possible to turn a transistor on and off—makes graphene ill-suited for digital electronic applications.
Researchers have known that bilayer graphene, consisting of two stacked graphene layers, acts more like a semiconductor when immersed in an electric field.
According to NIST researcher Nikolai Zhitenev, the band gap may also form on its own due to variations in the sheets' electrical potential caused by interactions among the graphene electrons or with the substrate (usually a nonconducting, or insulating material) that the graphene is placed upon.
Electrons do not move as well through substrate-mounted bilayer graphene; however, this may likely be compensated for by engineering the graphene/substrate interactions.
Stroscio's team plans to explore further the role that substrates may play in the creation and control of band gaps in graphene by using different substrate materials. If the substrate interactions can be reduced far enough, says Stroscio, the exotic quantum properties of bilayer graphene may be harnessed to create a new quantum field effect transistor.
* G. Rutter, S. Jung, N. Klimov, D. Newell, N. Zhitenev and J. Stroscio. Microscopic polarization in bilayer graphene. Nature Physics. Published online April 24, 2011.
** "See the Jan. 19, 2011, Tech Beat article "Real-World Graphene Devices May Have a Bumpy Ride" at www.nist.gov/public_affairs/tech-beat/.
Contact: Mark Esser email@example.com 301-975-8735 National Institute of Standards and Technology (NIST)