Graphene
Encyclopedia : G : GR : GRA : Graphene
Description
Graphenes can consist of only hexagonal cells, but if a pentagonal cell is present, then the plane warps into a cone shape; insertion of 12 pentagons would create a fullerene. Insertion of a heptagon causes the sheet to become saddle-shaped; controlled addition of pentagons and heptagons allows a wide variety of shapes to be made.Graphenes are interesting because carbon nanotubes may be considered to be graphene cylinders with a graphene cap (that includes a pentagon) at each end. Graphenes have also attracted the interest of technologists who see them as a way of constructing ballistic transistors. In March 2006, Georgia Tech researchers announced that they had successfully built an all-graphene planar field-effect transistor and a quantum interference device. Carbon-Based Electronics: Researchers Develop Foundation for Circuitry and Devices Based on Graphite March 14, 2006 gtresearchnews.gatech.edu [Link]
The IUPAC compendium of technology states: "previously, descriptions such as graphite layers, carbon layers, or carbon sheets have been used for the term graphene...it is not correct to use for a single layer a term which includes the term graphite, which would imply a three-dimensional structure. The term graphene should be used only when the reactions, structural relations or other properties of individual layers are discussed".
Writing in Science Novoselov, K.S. et al. "Electric Field Effect in Atomically Thin Carbon Films", Science, Vol 306 (5696), p. 666-669, 2004 DOI:[10.1126/science.1102896] , physicist Konstantin Novoselov and coworkers from the University of Manchester and the Institute of Microelectronics Technology and High Purity Materials at Chernogolovka state:
- Graphene is the name given to a single layer of carbon atoms densely packed into a benzene-ring structure, and is widely used to describe properties of many carbon-based materials, including graphite, large fullerenes, nanotubes, etc. (e.g., carbon nanotubes are usually thought of as graphene sheets rolled up into nanometer-sized cylinders). Planar graphene itself has been presumed not to exist in the free state, being unstable with respect to the formation of curved structures such as soot, fullerenes, and nanotubes.
Similar work is ongoing at Princeton University in Professor Ali Yazdani's laboratory by three researchers: Dan Kuncik, Josh Moskowitz, and Patrick Ho. Many of the results obtained by the Novoselov group in their PNAS paper "Two-dimensional atomic crystals" Novoselov, K.S. et al. "Two-dimensional atomic crystals", PNAS, Vol 102 (30), p. 10451-10453, January 26, 2005 DOI:[10.1073/pnas.0502848102] have been confirmed by the Yazdani group's work. For an example of a sample on the order of a monolayer, see figure 1.
This image was captured using a Digital Multimode AFM (atomic force microscope). Notice the step from the substrate at zero height to a graphene flake about 8 angstroms high, which is on the order of a monolayer.
Chemical modification
It is possible to prepare a soluble graphene form in the laboratory Solution Properties of Graphite and Graphene Sandip Niyogi, Elena Bekyarova, Mikhail E. Itkis, Jared L. McWilliams, Mark A. Hamon, and Robert C. Haddon J. Am. Chem. Soc.; 2006; 128(24) pp 7720 - 7721; (Communication) DOI:[10.1021/ja060680r] in a series of chemical modifications. First, microcrystalline graphite is treated with a stongly acidic mixture of sulfuric acid and nitric acid causing oxidation with an epoxidized sp2 carbon network in the center and carboxylic acid group at the edges of a graphene particle, and then exfoliation. The carboxyl groups thus created on the graphene surface are then converted to acid chloride groups by treatment with thionyl chloride; next, they are converted to the corresponding graphene amide via treatment with octadecylamine. The resulting material (circular graphene layers of 5.3 angstrom thickness ) is soluble in tetrahydrofuran, tetrachloromethane, and dichloroethane.References
See also
External links
- [Image Gallery - Graphite and Graphene]
- [BBC News report]
- [Electrons lose their mass in carbon sheets] Physics Web (09-Nov-2005)
- [In graphene, electron velocity is independent of energy.]
- [Potential for graphene computer chips, with explanation of technical issues/problems]
- [Quantum weirdness on the end of your pencil] Philip Ball, New Scientist Magazine issue 2559, (8 July 2006)
- For a full list of external links to MSDSs, spectroscopic data, commercial chemicals suppliers etc. for this compound, see [Chemical sources].
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