Graphene is a single planar sheet of sp² bonded carbon atoms. It is not an allotrope of carbon because the sheet is of finite size and other elements appear at the edge in nonvanishing stoichiometric ratios; a typical graphene would have the chemical formula C₆₂H₂₀. Graphenes are aromatic.

Graphenes may consist of only hexagonal cells but if a pentagonal cell is present 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.

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, physicist Konstantin Novoselov and coworkers from the University of Manchester and the Institute of Microelectronics Technology and High Purity Materials [1] 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.

The researchers went on to construct graphenes by mechanical exfoliation (repeated peeling) of small mesas of highly oriented pyrolytic graphite ; their motivation was to study the electrical properties of graphene. Mobilities of up to 10⁴cm²V ^{- 1}s ^{- 1} were reported; this value was almost independent of temperature.

References

• 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]

External link

• Image Gallery - Graphite and Graphene
• BBC News report