You may not have been aware, but this week is Graphene Week 2015, which marks a yearly week-long conference at the University of Manchester based around the emerging science and technological applications of graphene. This seemed as good a time as any to take a look at graphene: what it is, why some scientists are excited by its potential, and how it might make its way to your hands in the near future.
Even if you’ve not got a particularly scientific background, you’ve likely at least heard of graphene. Currently, it seems like not a week goes by without a new scientific study on graphene being published, or a new article coming out espousing its potential applications. It might seem hard to believe that graphene itself was only isolated just over a decade ago, back in 2003, by two scientists at the University of Manchester: Andre Geim and Konstantin Novoselov. The method of isolation was somewhat rudimentary: they peeled layers off of graphite, a form of carbon, using sellotape, and kept peeling layers away until they were left with graphene.
The paper in which they published their results was rejected twice by the journal Nature before publication. Previously, scientists had thought it would be impossible to isolate a stable two-dimensional structure. Six years after publishing the paper, Geim and Novoselov won the Nobel Prize in Physics for their findings.
At this point, we should look in more detail at what exactly graphene is. Graphite, the form of carbon most commonly found in the form of pencil leads, essentially has a structure consisting of many stacked layers of graphene. Graphene is the name used to refer to a single atom-thick layer of carbon atoms, bonded together in a hexagonal lattice patter that looks similar to a flat honeycomb, but which is a million times thinner than a piece of paper.
Of course, we’ve known about graphite for centuries, and even before graphene’s isolation in 2003, scientists had suspected that isolating single layers of graphene could be possible – but until that point, they hadn’t managed it. You might think that making graphene would be quite simple, considering the researchers at the University of Manchester were able to do it using sellotape, but mass-producing it is another matter. Producing high quality graphene in large amounts is a challenge that scientists are still working on solving. Whilst success has been announced several times, more cost-effective methods are still required,
So, what’s so great about graphene that we desperately want to be able to mass produce it? Graphene isn’t called a ‘wonder material’ for no reason – it has a number of superlative properties which scientists have married to a range of potential applications. It’s thin and flexible, yet stronger than diamond, and is in fact one of the strongest materials known, at around 200 times stronger than steel. This is despite it being very thin and lightweight; it weighs just 0.77 milligrams per square metre. It also conducts electricity and heat better than copper. It can come in a variety of forms: it can be wrapped into balls, rolled into tubes, or stacked to become graphite once again.
All of these properties led to a fanfare of potential applications in the initial years after graphene’s discovery. Its super-thin nature, and electrical conductivity, led to it being suggested as a replacement for the conductive indium tin oxide layers on touchscreens. It’s also had suggested uses in water filtration, as a replacement for silicon in transistors of electronic devices, in drug delivery, and in energy storage.
However, despite these potential applications, and all of the research on graphene, widespread applications in day-to-day life have yet to appear. This is for a variety of reasons. The first is the previously mentioned issues with mass producing graphene. Even when it can be mass produced with a degree of success, current methods can be costly. For example, phones with graphene-based touchscreens have been produced in China, but the method of producing them, by mixing methane gas and hydrogen then depositing layers on copper foil, is more expensive than the cost of indium tin oxide.
Graphene faces a bigger problem trying to overthrow silicon in transistors. Transistors can function as amplifiers or switches, and are triggered by electrical signals. Graphene transistors that are much faster than silicon transistors have already been produced, but they have an issue. Silicon has ‘bands’ of energy, in which its electrons can flow. It also has a gap between these bands. At low energies, electrons cannot flow between these bands, effectively allowing a silicon transistor to be switched off.
Graphene’s problem is that it does not contain one of these ‘band gaps’. This means electrons can flow through it at any energy; effectively, it cannot be switched off. This is a vital function for transistors, and whilst scientists have tried to artificially create a band gap in graphene, they have to this point met with limited success. Many scientists have now pinned their hopes for silicon replacement on other 2D materials, discovered since graphene, which do have a band gap.
Over a decade on from its isolation, graphene’s status as a ‘wonder material’ is coming under fire. Not everyone is convinced that it the costs of its production will ever be outweighed by a ‘killer’ application. Currently, the raw investment into graphene research is estimated at $2.4 billion; by contrast, a paltry $12 million-worth of graphene was sold in 2013. Many have pointed to carbon nanotubes, which when they were discovered had many suggested applications, but failed to fulfil much of the expectation surrounding them.
Whilst graphene may not have fulfilled its potential yet, there’s still time for it to do so – and with the volume of current research being done, it’s still entirely possible. The discovery of a cheap and efficient method of producing high-quality graphene on an industrial scale could have a drastic impact, and it’s also possible that someone could dream up an application that only graphene can fulfil. It may now have competition in the field of two-dimensional materials, but it could still end up on top of the pile.
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References & Further Reading