Stone Age, Bronze Age, Iron Age – the history of mankind is closely associated with the discovery, development and use of materials. As far as material development is concerned, the modern era – in which we are still living today – and in particular the recent past have been characterised by numerous impressive achievements. Polymer-based materials, the career of which began in the middle of the 20th century and which influence our world more than practically any other material that has ever been created, are playing an outstanding role here. A new material is now stimulating our imagination. It is graphene, for which innovative minds are already predicting a bright future. The claim is that graphene has the potential to revolutionise fundamentally the technologies we use in our modern-day world. While graphene is proving to be an ideal partner when combined with plastic in this context too.
Graphene is one of the materials that have the greatest sex appeal at the present time, although it must be said that the scientific community is primarily interested in the intrinsic properties of a material, because a closer look reveals that graphene quite literally has the visual charms of a chain-link fence.
Graphene is extremely thin and extremely light, but it is harder than diamond even so. It is highly flexible and transparent, while it has greater tensile and tear strength than steel. Although it is a perfect conductor of electricity and heat, it is impermeable to gases. Such a property profile gives it tremendous potential – and not only for material scientists. There is serious interdisciplinary discussion that graphene has the capacity to turn our technological world upside down and to revolutionise it.
Politicians seem to be convinced by this as well: in the context of the “Future and Emerging Technologies Flagship Initiative”, the European Union (EU) has pledged billions to fund a programme to promote graphene research. All in all, more than 140 organisations from 23 different countries are participating, including universities, research centres and commercial enterprises. 66 more partners were recently added in a new round of applications.
It way well be difficult for non-experts to understand the incredible enthusiasm about graphene, primarily because the fundamental scientific aspects are relatively complicated. Things do, however, become clearer when a look is taken at the details concealed in the nanocosmos of the material. The Nobel Prize Committee was also convinced that the compound has such immense promise that it awarded the physicists Konstantin Novoselov and Andre Geim from Manchester University the most prestigious prize a scientist can obtain while still alive – the Nobel Prize in Physics – in 2010 in honour of their work about graphene.
To be completely accurate, attention should be drawn at this point to the fact that although Novoselov and Geim were right to be honoured for their achievements – which will be outlined in greater detail later on in this article – they were not the first scientists to set foot on the graphene “moon”. As long ago as 1859, B.C. Brodie had already talked about the lamellar structure of thermally reduced graphite oxide in the Proceedings of the Royal Society of London in 1859 , which was thus the date when the world of this new material was first discovered. Brodie’s theory was investigated by V. Kohlschütter and P. Hänni, who reported on their “(...) findings about graphite carbon and graphitic acid” as well as on the production of paper from graphite oxide in the German Zeitschrift für anorganische und allgemeine Chemie (“magazine about inorganic and general chemistry”) in 1918 . It is also worth mentioning the work done by G. Rüss and F. Vogt, who published initial electron microscope pictures of thin-layer lamellar graphene . It was, in turn, Hanns-Peter Böhm, who studied “the adsorption properties of very thin carbon films” [4, 5], who coined the term “graphene” and can thus be considered one of the founders of modern graphene research.
A look at the scientific details
What the physicists Konstantin Novoselov and Andre Geim from Manchester University discovered in the research for which they won the Nobel Prize has caused a tremendous stir in the scientific community, primarily because what they found was considered impossible: the formation of free, single-layer graphene crystals. Let us take a look here at the basic scientific principles: apologies, but a bit of chemistry is essential. Graphene is a very thin – more precisely – two-dimensional modification of graphite – which is, in simple terms, the material in pencils that we write with. Like diamond, graphite is one of the forms in which carbon occurs. Carbon occurs in pure (crystalline) form in nature, i.e. as diamond or graphite, as well as in chemically bonded form in carbonates, carbon dioxide, mineral oil, natural gas and coal. In the periodic table of the elements, carbon has the letter C and the number 6. It is in the 4th main group and the second period. This brief outline alone enables chemists to provide extensive information about the strong reactivity of the carbon. After hydrogen (H), carbon forms the most compounds of all the elements in the periodic table; hydrogen holds first place, because – as is a well-known fact – most carbon compounds contain hydrogen as well. One special feature of carbon that is worth noting in relation to graphene as well is that it has the ability to form chains and rings with itself and other elements and to form particularly stable compounds. Although this sounds trivial, it is not.
The carbon atoms in a diamond form a very stable three-dimensional network; it is no coincidence that diamond is one of the hardest materials found so far. The carbon in graphite is in turn networked not three-dimensionally but only in layers. These layers are in turn stacked on top of each other – like sheets of paper in a pile – and like such sheets of paper tend to adhere to each other loosely, e.g. via electrostatic charging; in other words, the carbon layers in graphite are only bonded together comparatively loosely too (hydrogen bond, van der Waals force), so that they can be separated from each other easily.
When looked at more closely, every individual one of these detachable carbon layers resembles a piece of chain-link fence, which each link being bordered by six carbon atoms. Basically, each honeycomb (this comparison is correct too) is akin to an aromatic benzene ring, although without having the latter’s specificity. In the past, it was assumed that the layers detached from a graphite compound were unstable; this has, however, proved to be inaccurate, as Novoselov and Geim demonstrated with their presentation of free, single-layer graphene crystals.
The way they did this is surprisingly simple. Broadly speaking, they removed and secured one of the top layers of graphite with the help of adhesive tape that they attached to a flat piece of graphite and pulled off quickly. The sticky side of the adhesive tape was then in turn pressed onto another adhesive surface and so on. What was left at the end as a result was a single layer of interconnected carbon atoms less than 50 nanometres thick, which is absolutely transparent but has numerous (commercially) useful properties, such as the ability to conduct electricity, which makes graphene an ideal material – combined with plastics, for example – for use in ultrathin solar cells, highly efficient computer chips or innovative mobile phones. Graphene could prove to be valuable in medical engineering, car manufacturing or aerospace applications too, however. More detailed information about the many different potential applications will need to be provided elsewhere at a later date. For the time being, let us dwell a little longer on the internal structure of graphene, before we draw attention to a fundamental problem.
What makes graphene so special – and so complicated
Anyone who takes a close look at a chain-link fence when it is not being stretched will notice that the links are not completely flat; they have a corrugated surface. Graphene has a corrugated structure too, but this is precisely what appears to give it the stability that was considered doubtful previously. Like chain-link fencing, graphene can in addition be rolled up lengthwise. This characteristic has potential that makes the wildest of dreams seem feasible: in the idea of building a lift from the surface of the earth into our planet’s orbit that is being considered seriously by space experts, discussions have been held about the use of nanotubes made from graphene. And since we are talking here about experimental thinking: if the number of carbon atoms (C) in the honeycomb of the graphene fence was reduced from six to five, the geometry created would be similar to a kind of carbon cage which would permit inclusions. These carbon cage structures are no longer a theory; they are known as fullerenes.
In a nutshell, graphene is considered to be one of the most promising materials available at the present time. The physicist Ute Kaiser, who has been working on the electron microscopic characterisation of graphene since 2007 as head of material science electron microscopy at Ulm University, thinks that there are good reasons for the gold rush feel that has developed in graphene research. In co-operation with the chemical company BASF and the nanomembrane manufacturer CMM Technologies, Bielefeld University is working on a project that aims to produce graphene nanomembranes – another extremely exciting area of application for graphene: project co-ordinator Andrey Turchanin from Bielefeld University reveals that nanofiltration is proving to be a very interesting proposition not only for water desalination but also for the filtration of other liquids, gases and biomolecules. Andrey Turchanin says that the challenge here is “to adapt the properties of the membrane precisely to the needs of many different applications by varying the pore size, the material structure and the material surface”.
This project is right in line with the EU’s objective, which is to get the “miraculous new material” (graphene) out of scientific laboratories and into everyday use as quickly as possible.
This is exactly where the big problem lies, however: the production of sufficient amounts of graphene at affordable prices. This is still proving to be difficult at the present time – and will continue to be so for the foreseeable future. Economic experts speculate that the market will be cornered by whoever succeeds in solving the problem.
This is what is driving developers and inventors all over the world. According to the IT magazine Chip, China is still in the lead at the moment with 2,200 graphene patents, followed by the USA with 1,700 patents and South Korea with 1,200 patents. The focal point is mainly the idea of making batteries, displays, touchscreens and smartphones more innovative with components made from graphene and boosting sales of them as a result.
It remains to be seen who will come out on top in the end. Maybe Germany, which has been involved in graphene research from an early stage? Some scientists in the country are at least developing interesting and unusual ideas for the production of graphene. Physicists from Saarbrücken, for example, are using a fingerprint as the starting point for the obtainment of graphene. [To the study]
The production of graphene is the key to success
Chemical vapor deposition (CVD) is the standard process for the production of graphene. In this complex and thus costly technology, a carbon gas is deposited on extremely thin metal foil in a vacuum. The graphene produced in this way is then detached from the substrate material and is transferred to a different substrate – preferably an insulator for electronic applications. So that this transfer process does not damage the graphene structure, substrate materials are of interest that only bond the single-atom carbon layer to their surface weakly. The disadvantage of this is that the process of depositing the carbon on the metal foil is made more difficult.
Back in 2009, physicists from Saarland University therefore co-operated with research scientists from Nottingham and Augsburg to develop an alternative graphite production process, that is based on the deposition of liquid carbon compounds (LPD, liquid precursor deposition). “In LPD, a synthetic carbon compound is applied to the substrate material in liquid form with the help of a syringe in such a way that a cohesive film of liquid is formed”, explains the Saarbrücken physicist Frank Müller. Following transfer to a vacuum, the original substances, which are also known as precursors, evaporate, leaving a single layer of molecules. They degrade gradually by increasing the temperature, until in the final analysis all that is left is carbon, which links to form the honeycomb graphene structure. “In this process, the substrates can absorb sufficient carbon to grow graphene from the liquid phase, even if they only bond the graphene to themselves weakly”, explains Frank Müller.
One advantage of the new method is that it also works on metal surfaces that have not been possible so far with the classic CVD process, such as silver. The graphene structure can therefore be removed without being damaged: “Graphene and the substrate material adhere to each other like two sheets of wet paper: it is easy to remove one of them without destroying the other one.”
In order to prove that LPD synthesis is a very resilient process that works even under the most unfavourable of conditions, the scientists from Saarbrücken carried out a daring experiment: instead of applying a synthetic carbon compound with a syringe, they tapped the sweaty tip of a finger on the substrate material once. “A fingerprint on the sample is normally taboo in surface analytics”, says Frank Müller. He points out that sweat consists of an uncontrolled blend of many complex carbon compounds, including fatty acids and salts. In spite of these unfavourable test conditions, Frank Müller describes what the scientists discovered as follows: “The fingerprint fluid works just as well in LPD synthesis as a synthetic precursor”.
“With our fingerprint experiment, we have taken this method to its limits and have succeeded in demonstrating that it works even then.” The most important conclusion: “With the LPD process, it is also possible to use substrates that have not been feasible up to now with the classic CVD method.”
This opens up new possibilities for transferring graphene to other substrate materials – an aspect that is considered to play a central role in the context of the current EU research initiative “Graphene flagship”. “With respect to our own studies, we intend to use graphene layers prepared in this way to make a special investigation of the interaction with such biomaterials as proteins or bacteria”, says Karin Jacobs, Professor of Experimental Physics in Saarbrücken.
Definitely an interesting, innovative approach. But the question still has to be answered when it can be expected that graphene will be produced on an industrial scale and when we will be experiencing graphene as an integrated feature of our everyday lives. This remains to be seen. The Nobel Prize winners think that it is advisable to be patient: the development of a new material until it is suitable for everyday use could easily take 40 years. We will see ...
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 Benjamin C. Brodie: On the Atomic Weight of Graphite. In: Proceedings of the Royal Society of London. 10, 1859, S. 249 (JSTOR 108699).
 V. Kohlschütter, P. Hänni: Zur Kenntnis des Graphitischen Kohlenstoffs und der Graphitsäure. In: Zeitschrift für anorganische und allgemeine Chemie. 105, Nr. 1, 1918, S. 121–144, doi:10.1002/zaac.19191050109.
 G. Rüss und F. Vogt: Höchstlamellarer Kohlenstoff aus Graphitoxyhydroxyd.. In: Monatshefte für Chemie. 78, Nr. 3–4, 1947, S. 222–242.
 H. P. Böhm, A. Clauss, G. O. Fischer, U. Hofmann: Das Adsorptionsverhalten sehr dünner Kohlenstoffolien. In: Zeitschrift für anorganische und allgemeine Chemie. 316, Nr. 3–4, 1962, S. 119–127, doi:10.1002/zaac.19623160303.
 H. P. Böhm, R. Setton, E. Stumpp: Nomenclature and terminology of graphite intercalation compounds. In: Pure and Applied Chemistry. 66, Nr. 9, 1994, S. 1893–1901.