(Editor's Note: Scientist Live is launching a new, interactive feature, The Scientist Audio Mailbag. Here's how it works: Each week, we select a current news item and then arrange an interview with the researcher involved in the study. Scientist Live readers will be allowed to mail in questions to be presented to the scientist. The editors will then select a handful and pose them to the researcher. You will be able to hear their answers in their own words. Our first Mailbag deals with a promising new anti-HIV gel. Join the discussion now.)
Graphene, a single-atom-thick sheet of carbon, holds remarkable promise for future nanoelectronics applications. Whether graphene actually cuts it in industry, however, depends upon how graphene is cut, say researchers at the University of Illinois.Graphene consists of a hexagonal lattice of carbon atoms. While scientists have predicted that the orientation of atoms along the edges of the lattice would affect the material's electronic properties, the prediction had not been proven experimentally.
Now, researchers at the U. of I. say they have proof.
"Our experimental results show, without a doubt, that the crystallographic orientation of the graphene edges significantly influences the electronic properties," said Joseph Lyding, a professor electrical and computer engineering. "To utilise nanometre-size pieces of graphene in future nanoelectronics, atomically precise control of the geometry of these structures will be required."
Lyding and graduate student Kyle Ritter (now at Micron Technology Inc. in Boise, Idaho) report their findings in a paper accepted for publication in Nature Materials. The paper is to be posted on the journal's Web site on Sunday (Feb. 15).
To carry out their work, the researchers developed a method for cutting and depositing nanometre-size bits of graphene on atomically clean semiconductor surfaces like silicon.
Then they used a scanning tunnelling microscope to probe the electronic structure of the graphene with atomic-scale resolution.
"From this emerged a clear picture that edges with so-called zigzag orientation exhibited a strong edge state, whereas edges with armchair orientation did not," said Lyding, who also is affiliated with the university's Beckman Institute and the Micro and Nanotechnology Laboratory.
"We found that pieces of graphene smaller than about 10 nanometres with predominately zigzag edges exhibited metallic behaviour rather than the semiconducting behaviour expected from size alone," Lyding said. "This has major implications in that semiconducting behaviour is mandatory for transistor fabrication."
Unlike carbon nanotubes, graphene is a flat sheet, and therefore compatible with conventional fabrication processes used by today's chipmakers. But, based on the researchers' experimental results, controlled engineering of the graphene edge structure will be required for obtaining uniform performance among graphene-based nanoelectronic devices.
"Even a tiny section of zigzag orientation on a 5-nanometre piece of graphene will change the material from a semiconductor into a metal," Lyding said. "And a transistor based on that, will not work. Period."
