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Ballistic Transport in Graphene Suggests New Type of Electronic Device

CNMS user studies electron flow in graphene nanoribbons.

Oak Ridge National Laboratory

Conceptual drawing of an electronic circuit comprised of interconnected graphene nanoribbons (black atoms) that are epitaxially grown on steps etched in silicon carbide (yellow atoms). Electrons (blue) travel ballistically along the ribbon and then from one ribbon to the next via the metal contacts. Electron flow is modulated by electrostatic gates.Image courtesy of Georgia Tech/John HankinsonUsing electrons more like photons could provide the foundation for a new type of electronic device that would capitalize on the ability of graphene to carry electrons with almost no resistance even at room temperature – a property known as ballistic transport.

Research reported in the journal Nature shows that electrical resistance in nanoribbons of epitaxial graphene changes in discrete steps following quantum mechanical principles. The research shows that the graphene nanoribbons formed by this technique act more like optical waveguides, allowing electrons to flow smoothly for long distances in the material without scattering. In ordinary conductors such as copper, resistance increases in proportion to length, as electrons encounter more and more impurities that cause them to scatter while moving through the conductor.

The ballistic transport properties, similar to those observed in cylindrical carbon nanotubes, exceed theoretical conductance predictions for graphene by a factor of 10. The properties were measured in graphene nanoribbons approximately 40 nanometers wide that had been grown on the edges of three-dimensional structures etched into silicon carbide wafers.

“This work shows that we can control graphene electrons in very different ways because the properties are really exceptional,” said Walt de Heer, a Regent’s professor in the School of Physics at the Georgia Institute of Technology. “This could result in a new class of coherent electronic devices based on room temperature ballistic transport in graphene. Such devices would be very different from what we make today in silicon.”

The research was done through a collaboration of scientists from Georgia Tech in the United States, Leibniz Universität Hannover in Germany, the Centre National de la Recherche Scientifique (CNRS) in France and the Department of Energy’s Oak Ridge National Laboratory.

The full news release from Georgia Tech is available at http://www.news.gatech.edu/2014/02/05/ballistic-transport-graphene-suggests-new-type-electronic-device.

As a user of ORNL’s Center for Nanophase Materials Sciences, de Heer and his group performed a portion of the study’s microscopy research at the CNMS's four-probe scanning tunneling microscopy facility.

“Graphene and related two-dimensional materials have been a fascinating playground for scientists to explore novel electronic and transport properties over the last decade,” said ORNL’s An-Ping Li, a coauthor on the Nature study. “It is exciting to see that the basic research is now bringing real applications for these materials into the horizon.

The suite of scanning probe microscopy facilities at CNMS enables us to tackle cutting-edge challenges in nanoscience and closely interact with leading scientists like Professor de Heer. These strong interactions with engaged users serve very well in extending the reach of our scientific effort.”