The Graphene Revolution

The weird science of the ultra-thin

Brian Clegg

• Publisher: Icon Books
• Year: 2018
• ISBN:
  9781785783777
• Topic: Physical Sciences
• Subtopic: Physics
• Index: Physics

In 2003, Russian physicists Andre Geim and Konstantin Novoselov found a way to produce graphene – the thinnest substance in the world – by using sticky tape to separate an atom-thick layer from a block of graphite.
Their efforts would win the 2010 Nobel Prize for Physics, and now the applications of graphene and other 'two-dimensional' substances form a worldwide industry. Graphene is far stronger than steel, a far better conductor than any metal, and able to act as a molecular sieve to purify water. Electronic components made from graphene are a fraction of the size of silicon microchips and can be both flexible and transparent, making it possible to build electronics into clothing, produce solar cells to fit any surface, or even create invisible temporary tattoos that monitor your health.Ultra-thin materials give us the next big step forward since the transistor revolutionised electronics. Get ready for the graphene revolution.

1

THE STICKY TAPE SOLUTION

Big science–little science

There was a time when a lone scientist, or a handful of individuals working in a lab on a shoestring budget, could achieve wonderful things. Think of pretty well any scientific discovery that was made before the Second World War and you’ll find that neither finance nor staffing were huge. However, it would be easy to think that the hot science subjects of the 21st century all require massive budgets and enormous teams. This book is about a subject that has shattered this assumption.

Think back to the major announcements that were made in science since 2000. Early on in the century, the Human Genome Project published its results, with drafts from both the $3 billion public programme and the $300 million private Celera programme released jointly in 2001 after many years of work. In 2013, the team working on the Large Hadron Collider at CERN near Geneva, often called ‘the biggest machine in the world’, announced the discovery of a particle consistent with a Higgs boson. The collider and the staff working on it have cost over $5 billion to date.

Similarly, in 2016 and 2017 we have had a number of announcements of discoveries of gravitational waves made from the LIGO observatories, built at a cost of over $1 billion and with over 1,000 scientists worldwide involved in the project. And all of this is dwarfed by the funding that has been piled into the International Space Station which has cost over $100 billion without a single major scientific discovery to its name.*

So, what could two physicists working in Manchester, England achieve with a negligible budget, some blocks of graphite and a few rolls of sticky tape? It would turn out to be rather a lot – perhaps the most far-reaching technological breakthrough of the 21st century to date. The development of ultrathin materials that emerged from the Manchester work has far greater practical value than any of the multi-billion dollar experiments named above, yet also contributes major steps forward in our understanding of both physics and chemistry. This is big-impact small science on a minimal budget.

The city of Manchester has a strong reputation for scientific discovery – particularly when working on the atomic scale. It was there that John Dalton put forward his atomic theory that transformed our understanding of matter in the early 1800s. Nearly a century on, in 1900, Owens College in Manchester, soon to become part of the Victoria University of Manchester, saw the opening of an all-new physics building, a state-of-the-art facility, complete with a remarkably modern ventilation system which used oil baths to remove the soot from the smoky atmosphere of the country’s leading industrial city.

It was in this laboratory that Ernest Rutherford discovered the structure of the atom and Niels Bohr made the first steps towards a quantum mechanical understanding of atomic structure. Since then, all manner of scientific developments have followed in Manchester, from the construction of the Jodrell Bank radio astronomy observatory to Alan Turing’s work on computing. And it was that same Manchester University physics department† that unwittingly played host to Andre Geim and Konstantin (Kostya) Novoselov’s ‘Friday night experiments’ which led to the discovery of the new wonder material, graphene, followed by work on a range of other ultrathin substances.

These two Russian-born physicists first met when Novoselov was supervised by Geim on his PhD – which he was awarded in 2004 – at the Radboud University of Nijmegen in the Netherlands. Sixteen years older, Geim had by then already gained a considerable reputation for original science combined with quirkiness and lateral thinking. Nothing shows this more clearly than his use of both frogs and a hamster in his work.

Levitating frogs and co-authoring with a hamster – the quirky history of graphene’s discoverers

In 2000, ten years before he won the Nobel Prize for his work on graphene, Andre Geim won the Ig Nobel Prize for levitating frogs.‡ The Ig Nobel is a humorous award that has been presented since 1991 for scientific research that ‘first makes people laugh, then makes them think’.§ It is an entertaining reflection on strange-sounding research and has been won by scientific papers and inventions with citations such as ‘Can a cat be both a solid and a liquid?’, ‘Dung Beetles use the Milky Way for Orientation’ and ‘Determining the ideal density of airborne wasabi (pungent horseradish) to awaken sleeping people in case of fire or other emergency.’ What Geim demonstrated was that magnetic levitation of living organisms – and particularly frogs – was perfectly possible.

Anyone who has played with a pair of magnets knows that when they are aligned north pole to north pole, or south pole to south pole, they repel each other. If strong enough magnets are kept in alignment, one can be made to hover above the other. This clearly has potential practical applications. The idea that the repulsion effect could be used to get a train to hover over its tracks has been around since the start of the 20th century and a number of prototype ‘maglev’ (magnetic levitation) trains have run over the years. However, large-scale commercial application is only just becoming feasible with the development of ultra-powerful superconducting magnets. The Chuo Shinkansen line in Japan, which is expected to run at speeds of up to 500 miles per hour, is under construction at the time of writing.

To get many tonnes of train to float above the rails requires a lot of power – but it involves conventional magnetic repulsion between a magnet and pieces of metal, in which the magnet induces a magnetic field, a process familiar to Michael Faraday. But we all know that magnets don’t work on living things – so how could Geim, with his then collaborator Michael Berry of the University of Bristol, get a frog to float in mid-air using only a powerful electromagnet?

It’s worth thinking first about the way that different metals react to magnets. Iron, for example, has a strong response to magnetism, while copper – which like iron is a good electrical conductor – does not. This primarily reflects the way the electrons are grouped around the atoms of these metals. As we will see in more detail on page 33, atoms have ‘shells’ occupied by electrons, and each shell has a limited capacity. Copper has a single electron in its outer shell, which can be easily detached to conduct electricity, but this leaves a full outer shell, which means that the copper atoms in the lattice structure that make up a piece of the metal are relatively symmetrical. When iron loses an electron for conduction, though, its outer shell is not full – this means there’s a degree of asymmetry in the atoms, and each atom can act like a tiny magnet, lining up under the influence of a magnetic field.

Frogs and other living things, by contrast, aren’t made of metals (apart from small amounts in the blood etc.) – but frogs are made up of atoms and molecules which have attached electrons. Particularly handy is the asymmetric structure of water. In a strong magnetic field, water molecules will tend to line up and oppose the initial field that is acting on them, forming a weak magnet, a phenomenon known as diamagnetism. The effect is billions of times smaller than the field induced in a magnetic metal, but if the magnet influencing the frog is strong enough, the effect is sufficient to overcome the remarkably weak force of gravity.¶

A spare-time look at an unlikely interaction between magnets and water was the original stimulus for Geim to begin his work on frogs. He notes that it had been claimed for some time that putting magnets on taps and water pipes would prevent a build-up of limescale (and indeed many products are available online which claim to do just this). But it was hard to understand why they would work and many suspected that they were just ways to make easy money. As Geim put it: ‘The physics behind [the action] remains unclear, and many researchers are sceptical about the very existence of the effect.’ Never one to be put off by opinion, Geim attempted several unsuccessful experiments on the effect and eventually commented that he still had nothing to add to the argument. But the process got him thinking laterally about water, particularly as his day job involved working with extremely powerful magnets – that is, magnets 200 times stronger than a typical modern high-strength neodymium magnet.

Frogs were chosen as the subjects for the experiment because they are light, have a high water content as animals go, and because, to put it bluntly, there would have been less of a problem if they had ended up exploding than there would from experimenting on people or puppies. And it was much easier to build a magnetic ‘cup’ using electromagnets to support a frog in mid-air than it would have been to levitate a human. The first subjects for the experiment, though, were less likely to catch the attention of the media – simple drops of water. Geim noted in his Nobel lecture: ‘Pouring water into one’s equipment is certainly not a standard approach, and I cannot recall why I behaved so “unprofessionally”. Apparently no one had tried such a silly thing before …’ His colleagues immediately suggested he could try the experiment out on drops of beer as a follow-up experiment. It is not recorded whether Geim gave this a try, though it would have been entirely in character for him to do so.

A more realistic concern once moving on from globules of liquid to living things is that the extremely strong magnetic field would set up electrical currents in the brain. This is observed in a medical process known as transcranial magnetic stimulation. Powerful magnets positioned near to the skull do have a significant effect, starting electrical currents flowing in the cranial tissue. At low levels these can have beneficial effects, and are useful to apply a non-invasive prod to the brain, but with a strong enough field, the induced currents can cause seizures. However, the frogs seemed unharmed in the experiment.

Although Berry and Geim’s study was a serious piece of work (and deals with diamagnetic|| materials in general, not just the headline floating frogs), some of Geim’s sense of humour still managed to creep into the mostly very sober paper that the pair wrote on the subject. Here we are told: ‘[Using the effect on living organisms] could cause strange sensations; for example, if [the magnetic susceptibility** of flesh is greater than the magnetic susceptibility of] bone, the creature would be suspended by its flesh with its bones hanging down inside, in a bizarre reversal of the usual situation that could inspire a new (and expensive) type of face-lift.’

The following year, Geim confirmed his reputation for injecting levity into what was otherwise serious work when he wrote a paper for the very straitlaced Physica B: Condensed Matter journal on ‘Detection of earth rotation with a diamagnetically levitating gyroscope’ (a more practical application of levitation). His single co-author for this paper was named as H.A.M.S. ter Tisha – in other words, his pet hamster, Tisha.††

In a way, this recognition was an opportunity to reward Tisha for the animal’s contribution to earlier levitation research efforts. Tisha had been the first test subject for living organism levitation, but had appeared distressed by the experience. As Geim would later put it: ‘First we used a hamster. After we saw the hamster didn’t like it, we took a frog.’ The frog, it seems, was more phlegmatic about the whole thing.

Pencil thin

The work that won Geim and Novoselov their Nobel Prize was on graphene, a sheet of graphite – one of the crystalline forms of carbon – just one atom thick. Graphite is a substance that we have all used at some time, though an oddity of history means that we are more likely to call it ‘lead’ when it appears down the centre of a pencil.

At first glance, it isn’t obvious why anyone should associate graphite with lead. Lead is a dull grey metal, obviously not a material for drawing with, while graphite is carbon in the form of a black, shiny non-metallic material, not unlike coal in appearance. Sometimes, rather dubious guesswork has been used to come up with an explanation of why we call the writing bit of a pencil its lead. Perhaps the most plausible (if incorrect) suggestion is that it was because Romans wrote with a stylus that was made out of lead.

The better substantiated answer makes rather more sense. The natural lead ore galena is lead sulfide. (Because of impurities, as well as being the main source of lead, galena is also where much of our silver comes from.) Galena is a shiny black crystalline substance, which has a strong resemblance to naturally occurring graphite crystals.

When graphite was first discovered it was called plumbago or black lead, because it was actually thought to be a variant of galena. Though the distinction was pretty much cleared up by the 1770s, the name ‘lead’ stuck as the way we refer to pencil cores.

It should be fairly obvious that graphite is a useful material to make pencils from, even if you’ve never seen any. Its very name, coined in 1789 by German geologist...

Table of contents

• Cover
• Title Page
• Dedication
• Contents
• Acknowledgements
• 1: The sticky tape solution
• 2: The essence of matter
• 3: Quantum reality
• 4: Like nothing we’ve seen before
• 5: Other flatties
• 6: The ultrathin world
• Further reading
• Index
• About the Author
• Copyright