For “Ribbons” of Graphene, Width Matters
Thin widths change a high-performance electrical conductor into a semiconductor.
The Science
Cutting graphene, a one-atom thick sheet of carbon atoms, into thin nanostructured ribbons alters its electronic properties due to the creation of edges. Scanning tunneling microscopy characterization has shown how the electronic properties vary with nanoribbon width and pin-pointed the onset of semiconducting behavior.
The Impact
Graphene is touted for its potential to yield nanoscale devices. The demonstration of a tunable electronic structure opens up prospects for building energy-efficient devices from graphene ribbons.
Summary
Using scanning tunneling microscopy, researchers at the University of Wisconsin-Milwaukee have shown how to make very narrow zigzag ribbons of graphene that are only ten to a few tens of atoms across. They have achieved this feat by using iron nanoparticle assisted hydrogen etching of epitaxial graphene on silicon carbide. Using tunneling spectroscopy to measure the electronic properties of the ribbons, they found that new electronic and magnetic states are formed at the hydrogen-decorated edges, causing graphene to change from an efficient conductor to a semiconductor. The size of the semiconducting gap depends critically on the width of the ribbon. Above a threshold of 3 nanometers, a constant gap of 0.4 electron volt (eV) is found (compared to a gap of 1.1 eV for silicon – a well-known semiconductor); but for narrower graphene ribbons, the gap increases, up to 1.6 eV for a 1 nanometer ribbon, the largest bandgap found for the narrowest graphene zigzag ribbon ever made. The origin of this behavior is elucidated by first-principles calculations. These findings demonstrate the feasibility of tuning the properties of graphene, thus opening the door to building energy-efficient nanoscale devices from graphene ribbons.
Contact
Lian Li
University of Wisconsin-Milwaukee
lianli@uwm.edu
Funding
DOE Office of Science, Basic Energy Sciences.
Publications
Y.Y. Li, M.X. Chen, M. Weinert, L. Li, “Direct experimental determination of onset of electron–electron interactions in gap opening of zigzag graphene nanoribbons,” Nature Communications 5, Article number: 4311, 2014. [DOI: 10.1038/ncomms5311].
Related Links
http://www5.uwm.edu/news/2014/07/03/with-ribbons-of-graphene-width-matters-2/#.U8wiIPldWSo
http://www.microscopy-analysis.com/editorials/editorial-listings/stm-reveals-graphene-semiconductor
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