Self-assembly on graphene

Imagine a sculptor, stood inside his studio, a large block of marble in the centre of the floor. They want to create a statue. They approach the block and start removing pieces, discarding material until, after many hours, they have the finished article.

Now imagine an alternative reality. In this one, the studio floor starts empty. The sculptor is throwing tiny blocks of marble into the middle of the floor. The blocks start to assemble, and again, over many hours, a statue is constructed. In this reality, something has caused the blocks to assemble themselves into a grander structure.

The first of these realities is a an example of what we would call in nanotechnology a top-down approach. We start with a larger object and gradually remove material until we have the finished article. The second reality demonstrates the bottom-up approach, and, while it is unlikely to ever happen in the sculptor’s studio, it is very common when making nanomaterials.

In bottom-up synthesis the interactions between the individual blocks arrange each other into a grander structure. These structures can be used for many applications and their properties are determined by the arrangement of the blocks. To understand the final structure formed in bottom-up synthesis, it is important to understand the processes that make it.

There is a crucial moment in bottom-up synthesis. Imagine the blocks are forming on the floor, one next to the other. At some point, they will start to stack on top of each other. We would call this the 2D to 3D transition. It is flat when it is 2D, and at this transition point it becomes 3D.

This is interesting because lots of information is available about 2D structures formed through bottom-up synthesis. This is driven by the tools we have available for examining them. The best of these is scanning tunnelling microscopy (STM). In STM a sharp tip—so sharp the tip’s end is often a single atom—approaches the surface. We apply a voltage between the tip and the surface and then measure the electrons tunnelling between the two. This tunnelling current is very sensitive to the distance the electrons have to travel, and so STM gives us that important surface structure information. The difficulty arises when that film becomes thicker: that 2D to 3D transition. After a few layers, the information is all mixed and the information is muddled.

This is where other techniques would be used. In transmission electron microscopy (TEM), electrons pass through a material and are collected on the other side. These electrons are affected by their interactions with the material, and so can provide that structural information. TEM samples still need to be thin, but they can be up to 200 nm thick and still give useful information.

There is, however, a challenge to this approach, and its the reason TEM is not that popular for studying bottom-up synthesis. The electrons we use damage the material when they pass through because they have been accelerated to high speeds. This is particularly true for sensitive organic materials, the most commonly used materials for bottom-up synthesis. The damage can be so severe that all the information about the sample is lost almost immediately after being exposed to the energetic electrons.

We have been developing solutions to this problem. We use automation in the TEM to expose the sample to damaging electrons for the shortest possible time. More details of this are available in another post. Here’s how we used it to study bottom-up synthesis.

We were looking at two molecules TMA and TPA, and how they self-assemble on graphene. To start with we looked at how they self-assembled on graphene grown on copper. The graphene-copper surface is ideal for STM because the copper is flat and conducting. The STM showed how TMA and TPA arranged in their 2D structures. These patterns were expected and have been seen by other researchers before.

Scanning tunnelling microscopy of TMA (a) and TPA (c) on graphene. The chemical structures are shown in (b) and (d).

Now we have a look at them in the TEM. We deposited the TMA and TPA onto graphene that is now freely supported on a TEM grid. When we do this for a thin layer we see that the molecules have the same structure as those seen in the STM.

The surprising thing happens when we start to add more molecules onto the graphene. For TMA the diffraction patterns we take look no different: the molecules are arranging into layers just like the first one, and simply stacking on top of each other. The only change is that the patterns become easier to see as there is a greater signal from more molecules.

This is different for TPA: the patterns we measure start to change. Looking further we find that it is forming its bulk structure—that is the structure that large numbers of molecules form when they are allowed to arrange freely. Instead of adding more and more layers, a transition has occurred. The key point here is that TMA does not go through the same transition. It just keeps stacking molecules as before in their layers. It does not do the same transition to its bulk structure as TPA does.

Why does this happen for two molecules that are chemically very similar? We think that the difference lies within the different bulk structures of the two molecules. For TPA, the bulk structure is similar to the one seen for the single layers: the molecules are just tilted and packed closer together. However, for TMA, the bulk structure is distinctly different: it consists of molecules in planes that are interwoven. There is no easy way for the 2D layers to transform into this structure, and so it simply keeps packing layers onto each other.

This result implies that different 3D structures can be made by self-assembly by choosing the molecules in the beginning. The molecules are chemically similar but have a different transition.

Conference: Graphene Week 2017

From the 25th to 29th September last year, I attended the Graphene Flagship’s annual conference, Graphene Week. The conference was hosted in the centre of Athens, Greece, and featured a busy schedule of talks, posters and social events.

I presented my poster on my recent work using hexagonal boron nitride (hBN) as a coating to reduce the friction of steel components. The poster received interest from others at the conference who were also studying 2D materials in friction and wear applications.

Athens is a bustling city, and we managed to visit the main tourist attractions while we were there. A welcome reception was held at the recently refurbished museum at the base of the Acropolis. It’s easy to forget the extent of history that Athens possesses, and the monuments displayed were an enlightening reminder. Our guide demonstrated how the presentation of women in the statues, beginning as simply ornaments to becoming the structural pillars of buildings, reflected the societal attitudes towards women over that time.

The conference closed with a presentation of the next Graphene Week that will be help from the 10th to 14th of September, in San Sebastian, Spain. More details available here.

Conference: MMC 2017

Between the 3rd July and 6th July, I attended the Microscience Microscopy Congress 2017 (MMC 2017). This is the third time I have attended this series and it was as enjoyable as before. There were great talks, but also a huge industrial exhibition, which is great for finding out about the latest products that are available.

I presented a poster on my recent paper “Monolayer-to-thin-film transition in supramolecular assemblies: the role of topological protection”.

Find out more information about the MMC series here.

 

The Best Books on Scientific Writing

Writing is the most important academic skill. It is what helps the paper get accepted, the CV secure the job, and the proposal win the funding. But it is a skill that is neglected, often seen as an inherent attribute that cannot be significantly improved. However, it is a skill that can – and should – be developed through regular learning and practice.

I decided I wanted to improve my writing during the later stages of my PhD because I knew I was substandard and I wanted to be better. I attended a writing course at university that set me on the path of improved writing. And after this I turned to books. There are a lot of books on writing: even narrowing the scope to those for graduates writing specifically science leaves many choices. The list below are the five books that have resonated with me while I tried to develop my writing. I found useful tips, but, more importantly, they often contained exercises: practices that can be done to hone this skill.

Scientific Writing and Communication by Angelika Hofmann

This is my favourite book for improving writing, and it is essential for any scientist. It is packed with details on every aspect writing, stuffed into 700 dense pages. Each part is brilliant, but my personal favourites are parts two and three. In these the plans for the structure of a scientific paper are laid out. These plans are useful when struggling to start a manuscript. They explain how to start by organising all the ideas of what you want to write, how to then group these ideas into paragraphs, and then how to link the ideas in sentences within the paragraphs.

Further it has detailed help for writing papers (include review papers), grant proposals, posters, presentations, figures, and even job applications. There is also a chapter on helping English as a Second Language (ESL) learners.

Academic Writing for Graduate Students by Swales and Feak

This is an excellent book for practice. It is almost a work book. It is full of great tasks, picking apart individual sentences to understand the learning point. The book also contains structures for many writing scenarios below the section level. They outline what they think is the ideal way to write a certain passage. For example, data commentaries (describing a figure): start with its location and a summary of it; highlight the bit you think is most important; then interpret and discuss the implications. These structures are useful when writer’s block is in the way of getting started. You just lay out the structure, and start filling in the ideas.

I also learned here about the flow from old to new information, how details show your expertise, and the situation-problem-solution-evaluation construction for an abstract/introduction.

Elements of Style by Strunk and White

This book is very short and concise, which makes it a great revision book to be reread frequently. Essential tips are laid out individually under succinct headings. My favourite example: 17. Omit needless words.

There is also a lot of discussion on style. For example, there is discussion of Thomas Paine’s opening sentence “These are the times that try men’s souls”. It explains how any rearrangement of this sentence dulls its effect “It is times like these that try men’s souls” etc. This is an eye-opening discussion of style that can be used to make scientific writing more enjoyable to read and more memorable.

Writing for Science by Robert Goldbort

This book is less of a work book, and includes more prose on why and how to improve writing skills. There are lots of small pieces of information that can help in many different areas. One thing this book has that the others don’t is that it covers a larger scope: there are sections on writing laboratory notes, workplace writing (like emails), and some mention of undergraduate writing.

Penguin Writer’s Manual

As the title says, it is a manual. First part contains rules on grammar and vocabulary. A good section in here where I learned quite a bit is the usage section. Getting the right word is quite important in science. A mistake I made was with simple (meaning uncomplicated), and simplistic (overly simplified). The second part has a little bit on style and application, and communication. This book contains quality, concise general writing advice.

 

The graphene production problem

Despite the many success and promises of graphene, it is yet to be widely used in mainstream devices. One of the big hurdles in this area is producing graphene. There are many methods to produce graphene, but they each have their problems: those that produce the highest-quality graphene cannot produce enough, and those that produce lots often give graphene that is too poor for most applications.

The original isolation method was the now-famous sticky tape method. Here, chunks of graphite are peeled away using sticky tape, and these are then placed onto a flat surface. More sticky tape is then pressed onto the chunks and peeled away again, giving thinner chunks. If this process is repeated, eventually there are flakes that are only a single atom thick. However, by this time the flakes are very small (only a few microns across) and they are buried within a crowd of thick flakes. This makes finding and investigating the flakes difficult. They are, however, of a very high quality and so this graphene is useful for early stage research. But it cannot make enough for any applications.

The question then becomes: is there a way to separate graphene sheets on a much bigger scale? The first steps in this direction came from chemical exfoliation. In this method, graphite is oxidised, which then allows water to move easily between sheets. With some stirring, the sheets then separate in water quite easily. Now there are many single layer sheets floating in solution. However, these sheets are not really graphene, they are graphene oxide. Removing the oxygen from graphene oxide is still providing many challenges and pristine graphene is yet to be recovered from graphene oxide.

Separating sheets without oxidising would be the obvious next step. Recent efforts have been made to do this using high shear mixing. Here, a mixer creates forces on the graphite layers that is strong enough to separate the sheets, and a surfactant (like soap) can coat the sheets to stop them from restacking. Again, this method often produces thin sheets, but the sizes are still too small (tens of microns) for many applications.

A route to large area graphene that has lots of promise is chemical vapour deposition. Here, metals are heated to 1000°C, and carbon-containing gases like methane are introduced. The metals break the gases down into carbon atoms, which then arrange onto the metal surface to form graphene. This method produces high quality graphene and has been scaled up to metre sizes. The downside here is that the graphene is attached to a metal surface, and efforts to transfer the graphene off have yet to be perfected. Further, growing graphene in this way on a non-metallic substrate are still in their infancy.

In summary, the current research efforts in graphene production are along these lines:

  • Can the oxygen on graphene oxide be removed completely, and yield perfect, high-quality graphene?
  • Can liquid exfoliation give bigger sheets, and more routinely give only single layer graphene?
  • Is there a way to transfer graphene perfectly, leaving no contaminants, wrinkles, or defects?
  • Can we find a way to grow perfect graphene on any surface that we want?

Using micro-ARPES on heterostructures

Some of the most interesting research into 2D materials involves their electronic properties. The electronic properties determine how charge carriers (like electrons) behave within them, and this then dictates how the materials will perform in electronic devices. The details of the electronic properties can be seen in the electronic structure of the material, and studying this structure attracts significant research efforts.

The electronic structure of many of the new 2D materials has been investigated, and attention now turns to how heterostructures behave. Heterostructures are the result of stacking (to form a structure) two or more different materials (hence hetero-). It will be heterostructures that make devices, not single materials on their own. Therefore, understanding how they interact, particularly how their electronic structures interact, will be essential for electronic devices.

The big challenge of looking at heterostructures is that they are very small. The most reliable way of making them currently involves mechanical exfoliation. This is where tape is used to peel off single flakes that are then place on top of each other. But the flakes are only a few microns across usually, and so the stacked areas end up even smaller. Techniques that look at areas this small are still under rapid development.

Schematic of a heterostructure. A single layer of WSe2 is placed on top of MoSe2. The heterostructure is then the overlapping region. In this experiment, the heterostructure was placed on graphite because it is flat and helps stop the heterostructure from charging.

This is particularly the case for investigations of the electronic structure. The most robust technique to give accurate, detailed information on the electronic structure is angle-resolved photoemission (ARPES). Here light is shined onto the surface, which causes electrons to be photoemitted. Measuring the properties of these electrons after emission gives information about their properties in the solid. But the light shining on the surface normally covers about a millimetre. This will not work with a heterostructure that is 1000 times smaller.

Recent developments have enabled the use of a focused beam of light down to a spot only microns across. Using this technique, called microARPES, we can put the light on the different regions of the heterostructure.

Panel A is an optical image of the heterostructure, which is about 5 µm long, near the blue H. The other panels show details of the electronic structure around this heterostructure. A key result is shown in panels F and G. In F, there are two lines labelled as W and M, whereas in G, it looks like there is only one line in the same place. This demonstrates that the heterostructure interacts more strongly when they are aligned to each other.

In our recent paper we used microARPES to study the electronic structure of a heterostructure made from MoSe2 and WSe2. The ARPES beam could then be placed onto the different regions of the sample so the electronic structure of the individual layers can be measured, as well as the heterostructure. With this we found that the two layers did interact with each other and changes in their electronic structure were observed.

These results show that it could be possible to tune the electronic band structure to give the specific properties required to fit an application. This band engineering will help design heterostructures to start to fabricate ultrathin transistors or LEDs.

10 key papers on: Graphene

1 Electric field effect in atomically thin sheets by Novoselov et al.

This was the paper that started the graphene field. It details how the now-famous sticky-tape method was used to isolate carbon films from graphite that had thicknesses down to a few atomic layers. Layers this thin were not thought to be thermodynamically stable, and showing that these films existed was a revelation that kick-started the field of graphene research. Notice how the title uses the term atomically thin carbon films, as the word graphene was not yet as famous as it would become.

Further to isolating the films, the authors also performed electrical measurements on the films. These showed that the films had very high charge-carrier concentrations (there are lots of electrons (holes) available to move charge) and very high charge-carrier mobilities (and they can move very fast). These measurements were the first inkling of graphene’s superb electrical performance. The authors could not confidently say they had isolated single-atom-thin sheets explicitly, but they did note that as the carbon films got thinner, their electrical performance got closer to what would be expected for a single layer of graphene. In an endnote, however, they did say that they thought the thinnest layers were probably monolayers, but impurities on the samples disturbed the measurements. Again this was the first suggestion that graphene’s exciting electronic structure was measurable.

Read more: https://arxiv.org/pdf/cond-mat/0410550.pdf

2 Two-dimensional atomic crystals by Novoselov et al.

This paper followed from Manchester a year later, and within, the power of mechanical exfoliation (the sticky-tape method) was revealed. Here they didn’t just look at carbon layers from graphite, but they managed to repeat the procedure with other layered materials like MoS2 and NbSe2. They also showed how transmission electron microscopy could be used to count the edges of the films, using an example of a double layer of MoS2. Further, atomic force microscopy showed steps on the surface of the material that are the same as the distance between layers in a thick crystal. Overall, this paper showed directly how mechanical exfoliation could be used to separate films of layered materials and how direct imaging tools could show the number of layers in the films.

Read more: https://arxiv.org/pdf/cond-mat/0503533.pdf

3 Two-dimensional gas of massless Dirac fermions in graphene by Novoselov et al.

While the first paper on this list suggested some of graphene’s exciting electrical possibilities, it was this paper that outlined them in detail. The key part of this is to do with what equations from quantum mechanics can be used to describe the behaviour of charge carriers in a material. This understanding is important because the application of quantum mechanics to charge carriers in materials is what led to the use of semiconductors in transistors, which then caused the staggering rise in technology over recent decades. The exciting thing about graphene is that the equations we use to describe its charge carriers are different from those normally used. This paper shows how they are best described as relativistic particles with zero rest mass, which is extremely unusual for materials. It is this property that makes graphene such an excellent conductor. This result is not just exciting for graphene’s prospects as a new material, but also because it demonstrated the possibility of examining quantum physics on a small-laboratory scale.

Read more: self-archived version, Nature

4 The rise of graphene by Novoselov and Geim

This is a brief review of the progress in graphene research in the three years since it had been first isolated. It is from the perspective of Kostya Novoselov and Andre Geim (also authors of the previous three papers), who would go on to win the Nobel Prize in Physics in 2010 for the isolation of graphene. This gives this paper a unique perspective on where they think the field of graphene research is headed. The understanding of graphene’s properties had been developed and some of the possible application routes had been explored. Despite the progress, as they say, experimental work was yet to catch up with theory as new techniques and handling processes for the new material were still in their early days. This caused them to dampen some of the hype that was surrounding graphene at the time, reminding us that electronic devices were still 20 years away. The final paragraph claims we have only uncovered “the very tip of the iceberg” and that graphene is not a fleeting fad, a view that has been confirmed over the last decade.

Read more: Nature Materials

5 Fine structure constant defines visual transparency of graphene by Nair et al.

One of graphene’s exciting properties is its transparency, because materials that are strong, conductive, and transparent are rare. They are, however, important, as they are essential in technologies like touch-screens and solar cells. This paper published how much light a layer of graphene absorbed (2.3%), and how each extra layer absorbed a further 2.3%. They also explained the origin of this absorption, which again lies in graphene’s unique electronic structure.

Read more: self-archived version, Science

6 Measurement of the elastic properties and intrinsic strength of monolayer graphene by Lee et al.

This paper was the first to measure the mechanical strength of a monolayer of graphene, and they found that it did have the extremely high strength that was theoretically predicted. To do this, they started by suspending monolayer graphene sheets over holes cut in silicon. Then they used an atomic force microscope to press a sharp tip on to the sheet. They used this to measure how the sheet bends while being pressed, and also at what point the sheet broke. Graphene turned out to be the strongest material ever measured, which is outstanding considering it is only a single atom thick.

Read more: self-archived version, Science

7 The electronic properties of graphene by Castro Neto et al.

This review article lays out the theory behind the electronic structure of graphene, which had now been carefully explored by both theorists and experimentalists. The first part gives a concise review on the work leading up to this paper, with a focus on the electronic properties. It is the second part that introduces the basics of the theory of graphene’s electronic properties, including the effect of reducing the size of the graphene sheet (like in nanoribbons) and the effect of magnetism. Later parts look at deviations from the pristine graphene system, with the introduction of disorder.

Read more: https://arxiv.org/pdf/0709.1163v2.pdf

8 Large-area synthesis of high-quality and uniform graphene films on copper foils by Li et al.

One significant challenge with graphene technology is its production. The original exfoliation method can yield perfect graphene, but only in tiny sheets; another route, chemical production methods, can yield substantial volumes of large sheets, but the graphene is often defective. This paper introduced the chemical vapour deposition (CVD) method, which is currently the most technologically viable route to large-area, defect-free graphene. Since this paper, the method has been extended to making sheets of graphene 30-inches across, and even to producing them in a continuous roll-to-roll process.

Read more: https://arxiv.org/pdf/0905.1712v2.pdf

9 Graphene: status and prospects by Geim

Since the rush of results over the 5 years after its first isolation, graphene has attracted significant attention. This is mainly motivated by its single atom thickness, and its long list of superlative properties. It is these properties that are discussed in this accessible review, written by Andre Geim. An update on production, applications and basic science is presented. However, it is the focus on the prospects, especially from this perspective, that makes this article the most interesting. Speculating about all the possible applications and unexplored research areas makes this article an exciting read.

Read more: https://arxiv.org/pdf/0906.3799v1.pdf

10 Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems by Ferrari et al.

If you are interested to find out how far away graphene technologies are, this review will help. It has been compiled by over 60 authors from the Graphene Flagship – the 1 billion euro research effort, coordinated across Europe, into graphene’s (and related materials) properties and applications. The review aims to give an update on the progress in each of the Flagship’s areas, which include production, electronics, sensors, and biomedical applications. There are outlines of the basic science underlying each application, as well as examples of the technologies that are available. With over 2300 references cited, it is an extremely useful roadmap for the progress in graphene research.

Read more: Open Access from Nanoscale

Conference: ESOF 2016

ESOF2016The EuroScience Open Forum (ESOF), a biennial conference showcasing European efforts on science’s grandest problems, was this year hosted in Manchester. The city was chosen based on its long history of scientific advancement, from Rutherford’s proton discovery to the more recent isolation of graphene. I had never been to the ESOF series before, but the University promoted the programme and the topics looked diverse and interesting. Here I give a short overview of my experience.

The conference was held from 23rd to 27th July, almost one month after Britain had voted to leave the European Union, and this topic was mentioned on many agendas. In fact, a whole session was devoted to how scientific collaboration could continue post-Brexit. The majority of the scientific community felt the European Union benefited them, and the vote to leave cause concern for funding opportunities and international collaboration. Whether scientists did enough to get across how much we benefitted from the EU was discussed in this session, with the conclusion that it had not been portrayed strongly enough. Communicating the impact of science to the public is becoming increasingly important and there are important lessons to learn from the vote to leave the EU.

Looking towards the future, the panel highlighted three main proposals for success post-Brexit: after leaving the EU there would be an 850-million-pound shortfall in research funding that the treasury should fill; companies currently spend 1.7% on research and development, this should be 3 %; and finally that the movement of scientists should still be kept fluid. Like most Brexit issues the details are unclear and we will have to wait and see what happens in the coming months.

Another problem crossing international borders is doping in sports. At the time, news reports were highlighting the state-sponsored suppression of positive doping test results in athletes, and this brought some real interest to this topic. Talking here was Arne Ljungqvist, Olympic champion and ex-head of WADA, overviewing the challenges faced with by anti-doping. He gave a historical perspective about how doping is seen to be against the spirit of the Olympics, and also outlined the modern challenges faced with banned substances being found in many innocuous products.

It is not just Olympic athletes taking performance enhancing drugs, and later speakers highlighted how their use had permeated through society. Now the attraction of these drugs for amateur athletes and image-conscious young people has become a public health risk. They focused, again, on how it is important for scientists to communicate to the public what is known to be harmful about these drugs to improve the public health issue.

A later session discussed the overuse of another kind of drugs: antibiotics. Here the focus was on antibiotic resistance.  This is where over time, bacteria become resistant to the antibiotics we use to treat them through a simple mechanism. To remove a bacterial infection from someone, they can take antibiotics that kill the vast majority of the bacteria in the body. These simple medicines have saved millions of lives and simple infections are now rarely fatal. However, a tiny fraction of the bacteria are genetically resistant to the antibiotic and survive the treatment. These resistant bacteria could then grow into the strain that causes the next infection. This time the antibiotic will not work because of the bacteria’s inherited resistance. This in itself is not a huge problem, as we have tens of different antibiotics that can be used. But the more we use, the more resistant the bacteria become. Eventually we reach strains that cannot be treated with any of the antibiotics we possess. This is a worrying concern and would lead to a world where simple infections can kill.

In the session we learned that there are two prongs to tackle this problem. The first is to reduce antibiotic use to hinder the development of resistance. This means only using antibiotics when essential: for example not using them to improve growth rates in cattle, and only using them in humans to treat bacterial infections. How do we tackle some misinformation about antibiotics so people don’t ask for them to treat any illness? The second is to develop a new array of antibiotics.  Drug development is profit driven, and because antibiotics do not yield large profits they have remained undeveloped for 30 years. This is starting to change now as the issue begins to attract research funding. There was a reassuring showcase of drug development that could help this problem before it gets to the lethal stages.

Our scientific work is generating increasingly more information, both in volume and complexity. One main theme that spanned the whole of ESOF 2016 was this: how can we effectively get this information across for public benefit? How can we inform people that antibiotics are not helping most illnesses and that a resistance is developing which will have serious consequences? Or how can we convince them that leaving the EU will likely have a detrimental impact on scientific research in this country? Or that taking substances for image and sport performance improvements can lead to serious health consequences? There were many other questions like this, and as the science gets more complicated the feeling is that the scientist-public gap is widening. Narrowing this gap is a priority for all researchers if our science is to make the difference. Conferences like ESOF help in highlighting these issues, and allowing scientists to work together and share ideas on these things.

 

  • Watch videos of the sessions on YouTube:

Materials Week at University of Warwick

From 1st to 5th of February 2016, the University of Warwick organised Materials Week, a week of events focused on the emerging field of 2D materials. These included a workshop to discuss 2D materials in composites and electrochemistry; a colloquium by Professor Jonathan Coleman, a leader in the production of 2D materials; a lecture from Professor Sir Konstantin Novoselov, one of the two researchers who won the Nobel Prize in Physics for having started the 2D revolution; and many other exciting activities.

Image: graphene coated copper

Scanning electron microscopy (SEM) is an essential tool for studying graphene. It is particularly useful for graphene that has been grown on copper, as it gives a direct visualisation of the copper surface. The image below is an SEM image from a graphene coated surface. SEM images are normally presented as greyscale, but this one has been false coloured. The surface shows wavy lines of steps in the surface, just like terraced rice fields. The steps are caused by the interaction of graphene with the copper, and tell us that graphene is likely present in this area; without this, it would be challenging to infer whether graphene was there or not.

redhot_auto2

A scanning electron microscopy (SEM) image of a graphene coated copper surface. The graphene causes the copper to arrange into a stepped structure.