Graphene

Carbon is a fascinating material that is essential to life and can take many forms.

There are many different forms of carbon:

• Diamond

• Fullerenes

• Graphene

Carbon can create one of the hardest materials, diamond, and is the basis of all life on earth.

However it is Graphene which is by far the most useful and new form of carbon that caused scientists many problems when trying to obtain it.

What is Graphene?

It is basically a single layer of carbon atoms covalently bonded to three other carbon atoms with a free electron from each atom. Graphite, the stuff in the lead of your pencil is just layers of graphene stacked on top of each other. Here is an image of a graphene molecule:

http://media.wiley.com/Lux/53/287753.image1.jpg

Graphene has very unique properties that aren't shared by many other materials:

• Extremely high tensile strength (40 times stronger than diamond according to this website)

• Very flexible and stretchy

• Light absorbing

• A better conductor than copper

• Extremely lightweight

As you can see from the list above, graphene is and is going to be a very big deal in the modern world. Graphene is also the worlds first 2D material since it is only one atom thick. Before monolayer graphene was discovered in 2004 by Andre Geim and Konstantin Novoselov (winning them the Nobel Prize in Physics), it was thought that 2D molecules were impossible to obtain because they were supposedly thermodynamically unstable.

This is because there were many complex experiments since the 1970's trying to obtain monolayer graphene that all failed. In fact it was a very simple method that led to the discovery. Just to summarise the properties of graphene though, here is a short video.

How was Graphene Discovered?

Oleg Shklyarevskii suggested that the tape that he would use on graphite to expose clean surfaces had very thin layers of graphite on them. Novoselov tried to see how thin you could make the layers of graphite by repeated splitting of these graphite layers. It was then thought that maybe you could keep pulling apart these layers until you were left with single layers of graphene. In 2003 Geim and Novoselov discovered the worlds first monolayer of graphene using this method.

This makes graphene very easy and cheap in small quantities, however it is difficult to produce in large amounts. This is holding the world back in making graphene a commercial material and therefore stopping us from fully exploiting its extraordinary properties.

Now lets move on to exploring each of these.

High tensile strength

Every bond in a crystal of graphene is a super strong covalent C-C bond. If you want to pull apart a crystal of graphene in the same plane that the molecules are in, you need to break many of these bonds. This requires a huge amount of force because rather than the bonds in the material being inter-molecular, they are intra-molecular. This is the same property that makes diamond so strong. A sheet of graphene, like diamond, is made up of one single molecule meaning there are no weak inter-molecular forces that can be easily broken. Here is an image to illustrate these ideas.

If a single graphene crystal (one hexagon) was pulled apart by a shear force, the crystal would break down the plane of fracture shown above. This involves breaking covalent bonds which requires a lot of force explaining why graphene is such a strong material.

Light, Flexible and Stretchy

Graphene is only made of one layer of carbon atoms, so it is rather obvious and easy to understand that the material is very light.

With the flexibility and the ability to stretch, the hexagons of carbon atoms aren't rigidly kept in a flat plane. They can move up and down, left and right. This is because of the covalent bonds between the carbon atoms being able to move about and out of plane. Although the bonds themselves are rigid and cant stretch, the hexagons can stretch out and become irregular. This lets the crystal move and flex.

http://cdn.physorg.com/newman/gfx/news/2009/high-res1.jpg

The Best Conductor

Carbon atoms have 4 electrons available for bonding with other elements and molecules. When carbon is in its graphene form, 3 of these are involved in covalent bonds with other carbon atoms. This leaves one free electron to move between atoms above and below the graphene crystal. It is this electron that gives graphene its amazing conductive abilities.

The free electrons in graphene behave like they are massless. In this state they are known as Dirac Fermions. This lets them travel along the graphene sheets at roughly one tenth the speed of light. The ability for the electrons to move at such high speed is the reason that graphene is so very conductive. Graphene is more conductive than almost any other material in the world meaning the discovery of this property could revolutionise technology in the future.

Light Absorbing

So you might be saying, "why is it so impressive that graphene can absorb some light?". However you then remember that graphene is a single atom thick and then you realise that this property is actually very impressive and strange. Well done by the way.

This property is also due to the massless electrons that were mentioned before. A layer of graphene will absorb 2.3% of white light being shone through it. Furthermore, approximately an extra 2.3% will be absorbed with each subsequent layer of graphene added.

References:

• de La Fuente, J., Graphene & Graphite - How Do They Compare? [Online]. Available from: http://www.graphenea.com/pages/graphene-manufacturer-producer-supplier [Accessed 19 October 2013].

  • de La Fuente, J., Properties of Graphene [Online]. Available from: http://www.graphenea.com/pages/graphene-properties#.UmlPr1Drw6q [Accessed 19 October 2013].

  • Geim, A. K. and Novoselov, K. S., 2007. The rise of graphene. Nature Materials [Online], 6. Available from: http://www.nature.com/nmat/journal/v6/n3/full/nmat1849.html [Accessed 21 October 2013].

  • The University of Manchester, The Story of Graphene [Online]. Available from: http://www.graphene.manchester.ac.uk/story/ [Accessed 20 October 2013].

  • The University of Manchester, The Story of Graphene [Online]. Available from: http://www.graphene.manchester.ac.uk/story/properties/ [Accessed 20 October 2013].

Graphene video:

• https://www.youtube.com/watch?v=dTSnnlITsVg

Other images used were drawn using Microsoft Paint.