graphene (rus. графен) — flat single-atom-thick hexagonal latticeofsp2-hybridised carbonatoms; two-dimensional form of carbon.

Description

Graphene can be represented as a single atomic plane of graphite separated from the bulk crystal – a flat grid of hexagons with carbon atoms at the vertices. Each of them has three neighbours; three out of four carbons' valence electrons will be used to form bonds with those neighbours. The fourth electron participates in forming the -system of the graphene sheet, which determines its electronic properties.

Previously it was thought that two-dimensional structures could not exist in the free state due to the high surface energy, and must turn into three-dimensional structures, although they could be stabilised by applying on a substrate. Before 2004 all experiments on obtaining such structures failed. More recent studies have shown that there exists a whole class of two-dimensional crystals of various chemical compositions [2]. Graphene was obtained from graphite by means of monolayer stabilisation with substrates. Due to weak bonding between the graphite layers the graphite was then successfully split into thinner layers with use of an adhesive tape; then the tape was dissolved and graphene fragments were transferred to a silicon substrate. In 2010 Andre Geim and Konstantin Novoselov were awarded with the Nobel Prize for these works. Other methods are based on epitaxial growth during thermal decomposition of silicon carbide, epitaxial growth on metal surfaces, or chemically cutting open the nanotubes.

The interest in graphene is due to its electronic properties. Thus, it enables ballistic (i.e., practically without scattering) transport of electrons, whose characteristics are only very slightly influenced by the substrate and the environment. Specifics of the band structure of graphene explains the existence of electrons and holes with zero effective mass, which demonstrate quasirelativistic behaviour described by the Dirac equation. In addition, the anomalous quantum Hall effect is observed in graphene even at room temperature. Studies have shown that graphene is also a promising material for spintronics.

The properties of graphene can be varied by means of chemical modification [6]. The highest reactivity is observed at the edges of graphene fragments, although full or partial functionalisisation of the whole fragment can also be achieved. For example, graphene can be hydrogenated to graphane.

Over just a few years, prototypes of many promising graphene-based devices have been produced, including field-effect transistors with ballistic transport at room temperature, high-sensitivity gas detectors [7], graphene single-electron transistors [8], liquid crystal displays and solar cells with graphene as a transparent conductive layer [9] , spin transistors, and many others.

Authors

  • Goldt Ilya V.
  • Shlyakhtin Oleg A.

Sources

  1. Novoselov K. S., Geim A. K., Morozov S. V. et al. // Science. 2004. V. 306. P. 666.
  2. Novoselov K. S., Jiang D., Schedin F. et al. // Proc. Natl. Acad. Sci. 2005. V. 102. P. 10451.
  3. Geim A. K., Novoselov K. S. // Nature Mater. 2007. V. 6. P. 183.
  4. Novoselov K. S., Geim A. K., Morozov S. V. et al. // Nature. 2005. V. 438. P. 197.
  5. Zhang Y., Tan Y., Stormer H. L., Kim P. // Nature. 2005. V 438. P. 201.
  6. Elias D.C., Nair R. R., Mohiuddin T.M.G. et al. // Science. 2009. V. 323. P. 610.
  7. Schedin F., Geim A. K., Morozov S.V. et al. // Nature Mater. 2007. V. 6. P. 652.
  8. Ponomarenko L. A., Schedin F., Katsnelson M. I. et al. // Science. 2008. V. 320. P. 356.
  9. Blake P., Brimikombe P.D., Nair R. R. et al. // Nano Lett. 2008. V. 8. P. 1704.
  10. Morozov S. V., Novoselov K. S., Gejjm A. K. // Tezisy dokl. II Mezhd. foruma po nanotekhnologijam Rusnanotech'09, 2009. 444 pp.

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