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Graphene: Sheets of Carbon-based Nanoparticles

When carbon forms sheets when it bonds to three other carbon atoms they are called graphene. Nanotechnology researchers have only recently (2004) been successful in producing sheets of graphene for research purposes.

Common graphite is the material in pencil lead, and it’s composed of sheets of graphene stacked together. The sheets of graphene in graphite have a space between each sheet and the sheets are held together by the electrostatic force called van der Waals bonding.

Sheets of graphene held together by van der Waals bonding make graphite.
Sheets of graphene held together by van der Waals bonding make graphite.

Graphene sheets are composed of carbon atoms linked in hexagonal shapes with each carbon atom covalently bonded to three other carbon atoms. Each sheet of graphene is only one atom thick, and each graphene sheet is considered a single molecule. Graphene has the same structure of carbon atoms linked in hexagonal shapes to form carbon nanotubes, but graphene is flat rather than cylindrical.

A graphene sheet.
A graphene sheet.

Because of the strength of covalent bonds between carbon atoms, graphene has a very high tensile strength. (Basically, tensile relates to how much you can stretch something before it breaks.)

In addition, graphene, unlike a buckyball or nanotube, has no inside because it is flat. Buckyballs and nanotubes, in which every atom is on the surface, can interact only with molecules surrounding them. For graphene, every atom is on the surface and is accessible from both sides, so there is more interaction with surrounding molecules.

Finally, in graphene, carbon atoms are bonded to only three other atoms, although they have the capability to bond to a fourth atom. This capability, combined with great tensile strength and the high surface area to volume ratio, make it very useful in composite materials.

Researchers have reported that mixing graphene in an epoxy resulted in the same amount of increased strength for the material as was found when they used ten times the weight of carbon nanotubes.

A key electrical property of graphene is its electron mobility (the speed at which electrons move within it when a voltage is applied). Graphene’s electron mobility is faster than any known material and researchers are developing methods to build transistors on graphene that would be much faster than the transistors currently built on silicon wafers.

Another interesting application being developed for graphene takes advantage of the fact that the sheet is only as thick as a carbon atom. Researchers have found that they can use nanopores to quickly analyze the structure of DNA.

When a DNA molecule passes through a nanopore which has a voltage applied across it, researchers can determine the structure of the DNA by changes in electrical current. Because graphene is so thin, the structure of a DNA molecule appears at a higher resolution when it passes through a nanopore cut in a graphene sheet.

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