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Electronic Life on the Edge

Graphene nanoribbons are narrow sheets of carbon atoms only one layer thick. Their width, and the angles at which the edges are cut, produce a variety of electronic states, which have been studied with precision for the first time using scanning tunneling microscopy and scanning tunneling spectroscopy.

Led by the Materials Sciences Division's Michael Crommie, researchers have seen for the first time that electrons prefer to live on the edge---of graphene nanoribbons, a slim strip of carbon atoms arranged in a 'chicken wire' lattice just one atom thick. These findings show electrons confined to narrow channels along the edges of well-ordered graphene nanoribbons. This one-dimensional channeling of electrons could be beneficial for energy harvesting applications, such as solar cells. 

In graphene sheets electrons are free to move in two dimensions, allowing them to race across a plane.   In a nanoribbon, however, electrons can be confined along edges.  These edges are so close they interact, yielding band gaps like in semiconductors. This opens the possibility of manipulating nanoribbon edge electrons with electric fields and light in unique ways for potential applications including detectors, photovoltaics, and spin-based electronics.

A scanning tunneling microscope, which can resolve atomic structure and measure electronic properties with nanoscale resolution at a surface, was used to investigate individual atoms in meticulously crafted graphene nanoribbons with different edge geometries. By studying more than 150 nanoribbons, the team determined energy and distribution of electrons at a nanoribbon edge, answering fundamental questions regarding nanoribbon electronic properties. 

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Chenggang Tao, Liying Jiao, Oleg V. Yazyev, Yen-Chia Chen, Juanjuan Feng, Xiaowei Zhang, Rodrigo B. Capaz, James M. Tour, Alex Zettl, Steven G. Louie, Hongjie Dai, and Michael F. Crommie, "Spatially resolving edge states of chiral graphene nanoribbons," Nature Physics 2011 (advanced online publication, May 8, 2011).