Tuesday, 4 October 2011

Graphene Dream

Graphene has experienced a rise to fame faster than the lolcat takeover of the internet. Last year two researchers from the University of Manchester; Andre Geim and Kostya Novoselov received the Nobel Prize in Physics for groundbreaking experiments regarding the two-dimensional material graphene. The ‘upzipped carbon nanotube’ became a hot topic, producing over 3000 journal articles and slowly starting a new science band wagon rolling.  This was well and truly jumped upon by the UK government early this week with an announcement that they would pledge £50million towards developing spin-off technologies from the material.

This amount of funding will drive graphene development to new levels of omnipresence, with rumours that it will supersede our dependence on silicon; the other superstar Mousketeer of material science.  So how good is graphene and what exactly can we use it for?

Graphene is essentially a thin slither of graphite. Graphite is naturally occurring, known as the Class 1 grade of coal, and consists of carbon atoms. P.R. Wallace first theorised the existence of graphene in 1947 when he was studying the band structure of graphite. The graphene sheet is 1 atom thick and was not isolated and studied until the 2000’s, a prevalent trend in experimental research where with each decade you go a little bit more quantum.  This 2D sheet has broken many records by being the strongest as well as most thermally and electrically conductive material measured. These properties are due to an extremely high current density, meaning it can carry a large amount of electricity throughout its volume. Graphene also has the longest mean free path of any material, which is similar to comparing the traffic in Central London to the middle of the Sahara in terms of electrons being able to travel through a material undisturbed. This leads to low resistance and more conductivity. Some other properties which have dubbed graphene as the most useful thing since plastic are its transparency and elasticity.

The extreme properties of graphene have made it a material of interest in industry. There has been research conducted by IBM to make a touchscreen out of graphene, possibly paving the way for flexible screens, roll-up mobiles and batteries that feel like rubber. On the flip side, the strength of graphene will make it lucrative for composite fabrication and tyre strengthening. It has been claimed that a hammock sized sheet which would weigh less than 30 grains of salt would carry the averaged sized cat, a measurement standard which certainly impressed the cat lovers amongst us.

Cat hammock patents aside, there are some major hurdles that need addressing before we go graphene mad. The material has no band gap which means there isn’t a space between the valence band where electrons sit firmly within the structure, and the conduction band, where electrons move into and  gain some freedom to conduct electricity. This means graphene is constantly ‘on’ and conductive, a feature that will hold back electronic component development.

The main barrier will be large scale manufacture of graphene. The Nobel prize winners used a ‘mechanical exfoliation’ method which is basically using sellotape to tear flakes off a lump of graphite. The sellotape was then dissolved in acetone to leave a residue of graphene flakes onto a silicon wafer. It’s then pot luck if you find a nice patch where a single sheet has formed. Chemical vapour deposition growth and growth from solid carbon in a furnace are techniques which could change this fabrication process, but exactly how much change will this leave the £50million fund?

There is a history of ‘fad’ scientific developments which undergo a slow burn lifecycle despite early excitement. Does anyone remember carbon nanotubes? And how many of us can afford to have solar cells on our rooftops? Seen any nano-bots in your cornflakes recently? These are all research topics that genuinely will bring about great changes to the way we live. Graphene can now be added onto the same list. But the LASER is one of the few examples of something we have incorporated into our everyday lives, and that took a good 40 years. So whenever you hear of reports about the next big thing in science, please add a mental question mark to the end of it. And then wait and see.

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