Researchers found it difficult to fabricate the graphene structures and isolate sufficiently large individual sheets and to verify its unique 2D properties But, Andre K. Geim and Konstantin S. Novoselov, both at the University of Manchester, U.K., have succeeded in producing, isolating, identifying and characterizing graphene and have won this year's Nobel Prize for Physics.
Graphene
Carbon readily bonds with itself to form extended sheets of atoms comprising linked hexagonal rings by covalently bonding to its three nearest neighbors leading to a unique sheet structure is called graphene. Solid graphite is made up of layers of graphene stacked together. This carbon-carbon bond is the strongest among chemical bonds. Some of the electrons in the carbon-carbon bonds are free to move about the entire graphene sheet, rather than stay home with their donor atoms, giving the structure good electrical conductivity. Its Fermi surface is characterized by six double cones. In intrinsic (undoped) graphene the Fermi level is situated at the connection points of these cones. But the Fermi level can however be changed by an electric field so that the material becomes either n-doped (with electrons) or p-doped (with holes) depending on the polarity of the applied field. Graphene can also be doped by adsorbing, for example, water or ammonia on its surface. The electrical conductivity for doped graphene is potentially quite high.
The tight coupling between atoms in the carbon-carbon bond provides an intrinsic thermal conductivity that exceeds almost all other materials. The structure of a fullerene nanotube is that of a sheet of graphene, wrapped into a tube and bonded seamlessly to it. This is a true molecule with every atom in its place and very few defects: an example of molecular perfection on a relatively large scale.
Graphene is practically transparent. In the optical region it absorbs only 2.3 per cent of the light. In contrast to low temperature 2D systems based on semiconductors, graphene maintains its 2D properties at room temperature.
The discovery
The isolation of stable sheets of graphene was not thought possible earlier but Andre Geim, Konstantin Novoselov and their collaborators from the University of Manchester (UK), and the Institute for Microelectronics Technology in Chernogolovka (Russia), succeeded in doing this. They used a simple but effective mechanical exfoliation method for extracting thin layers of graphite from a graphite crystal with Scotch tape and then transferred these layers to a silicon substrate.
Eventhough this method was first suggested and tried by another group they were not able to identify any monolayers, but the Nobel prize winners were able to even identify flakes made up of a single layer and pattern into a Hall bar and connect electrodes to it.
Applications of Graphene
Graphene has a number of properties which makes it interesting for several different applications. It is an ultimately thin, mechanically very strong, transparent and flexible conductor and an interesting material for electronic high frequency applications. It can be used in applications such as touch screens, light panels and solar cells, where it can replace the rather fragile and expensive Indium-Tin-Oxide. Flexible electronics and gas sensors are other potential applications. Due to low weight it could also be used in satellites and aircraft fabrication.