From the Labs: Materials
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Bulk Graphene
Slicing carbon nanotubes into ribbons makes speedier transistors.
Source: “Longitudinal unzipping of carbon nanotubes to form graphene nanoribbons”
James M. Tour et al.
Nature 458: 872-876
Results: Researchers at Rice University have developed a simple method for making large numbers of long, narrow ribbons of graphene, a single-atom-thick film of carbon. They chemically sliced open carbon nanotubes, which are essentially rolled-up sheets of graphene.
Why it matters: Graphene conducts electrons faster than silicon, so it could be used to make faster transistors. But it’s been difficult to manufacture the semiconducting type of graphene that’s needed for this application. One way to make semiconducting graphene is to cut the material into narrow nanoscale ribbons, typically a slow process. The new chemical method produces bulk quantities of these ribbons by modifying carbon nanotubes, which are easy to manufacture in large amounts. The approach also solves a problem with carbon nanotubes: their electronic properties can vary widely. Unzipping them to make nanoribbons makes these properties more uniform.
Methods: The researchers exposed multiwalled and single-walled carbon nanotubes to sulfuric acid and potassium permanganate, a strong oxidizing agent. The resulting reaction breaks a carbon-carbon bond in each nanotube, and the exposed carbon atoms immediately bind to oxygen atoms, creating a strain on the adjacent carbon-carbon bonds. This strain causes the adjacent bonds to break more easily, and a chain reaction propagates down the length of the tube, cleanly unzipping it into a ribbon. This reaction repeats on each of the nanotubes’ walls, or concentric layers, yielding as many ribbons per tube as there are layers. The graphene nanoribbons must then undergo another reaction to remove the oxygen atoms. Finally, the researchers incorporated the nanoribbons into transistors using previously developed techniques.
Next steps: The researchers are developing thin-film and ink-jet printing methods for depositing nanoribbons, which would speed up the manufacture of graphene-based electronics such as radio-frequency identification tags.
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