Making Graphene: A brief look at the state of the art
Picture this: You stand between two trees in a garden; you are holding a pet cat. You gently hold out the cat and lower it down in front of you. You and the cat feel a gentle resistance as it rests on an invisible springy layer between the trees. It is safe to let go and you look at one another with puzzled amazement as your feline friend seemingly floats in mid air.
You’ll have gathered that this is not magic, it is a thought experiment devised by Andre Geim and Konstantin Novoselov who isolated graphene in 2004 and won the Nobel Prize in 2010 . You have just placed the cat on a hammock made of graphene strung between the two trees. The invisible layer is one atom thick, 200 times stronger than steel and this demonstration shows some of the capabilities of this remarkable new material.
And yet, for all this activity, the thought experiment with the cat has not been done for real. Why?
No surprise then that a global industry has sprung up around this wonder stuff with billions of dollars of investment pouring in to create the new graphene era.
Companies and Universities have immense resources focussed on graphene applications as evidenced by the numbers of patents – over 24,000 worldwide in the last 10 years, 9,000 of those being in 2014 alone .
The UK patent office has just done some excellent work visualising the patent landscape for graphene . It turns out that most of these patents are connected with applications for graphene rather than production methods.
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This means graphene is very tricky stuff to make in useable quantities. There are 3 known routes for making graphene, let’s call them ‘the 3 E’s
Exfoliation: This means peeling layers. Graphite is a source material for graphene. It is made of layers of graphene much like a deck of cards. In theory, the larger and more defect-free a block of graphite is, the higher the potential value as a source of graphene sheet. However no large-scale sheet production has been reported so far.
Large-scale graphene production is in the form of microscopic flakes of graphene sheared from graphite and sold as a suspension in a variety of liquids. These suspensions are a source of graphene for catalysis and biomedical research. At present I’m not aware of any process where the flakes recombine to form large sheets of graphene.
Exfoliation seems to have its limits.
Epitaxy: This means growing a graphene layer on a crystalline surface. The most commonly used method is Chemical Vapour Deposition (CVD) where hot methane gas deposits a graphene layer onto a hot copper surface. Once the surface is covered, no further graphene can form so this method naturally produces a single layer of graphene. The copper is either etched away or the graphene layer is ripped from the surface. Current production seems to be restricted to sizes around 40-50 square mm, is not defect-free and is rather time consuming.
Encausty: This means creating layers of graphene by burning an organic polymer film surface. Professors Jian Lin and James Tour at the University of Texas have recently discovered that burning a polyimide plastic film with a pulsed laser leaves a black deposit of graphite. They call this process Laser Induced Graphene (LIG) . The graphene layers can then be peeled away from the graphite. This process is right at the cutting edge of the field and produces graphene layers with 5 and 7 ring defects that they have found make the material suitable for super-capacitors that could be key to the next stage in battery development.
So, where does this take us?
The graphene research and development effort has been focussed on exciting and eye catching applications for the new material.
However creating the material at large scales is a tough problem that has not been solved yet. Claims of large-scale production are really suspensions of small particles of graphene that have some use, but won’t be the source of a full revolutionary advance in technology.
There is some indication of genuine progress in creating the graphene that all these patents need to realise their returns on investment. In the meantime I prefer to wait and watch.
How will we know whether true progress is being made?
Let’s go back to our thought experiment and gently return the cat to firm ground. The true promise of the new graphene era will start once someone demonstrates this experiment for real. I’d very much like to be there to see a cat float in mid air, wouldn’t you?
Adrian Nixon began his career as a scientist and is a Chartered Chemist and Member of the Royal Society of Chemistry. As a scientist and ... <Read more about Adrian Nixon>