For a material that continuously surprises scientists with its combination of properties – ultra-thin, conductive, flexible, strong, transparent – graphene is disarmingly simple to produce at the small scale.
The Nobel Prize winners who first isolated the single layer of carbon molecules did so by peeling sticky tape off a pencil lead, and other scientists have since devised methods that involve washing-up liquid and a kitchen blender.
The question now is how to scale up production of graphene to commercial levels. Professor Mar García-Hernández at the Materials Science Institute in Madrid, Spain, says scientists have a choice of ways to produce graphene, which yield different results.
‘We cannot refer just to graphene; there are many kinds of graphene depending on the kind of synthesis you have followed to produce that material,’ said Prof. García-Hernández. ‘Depending on that, you get different grades of the materials. One or two are superb, you will see them in electronics and so on; others are not so good but still they are very useful for many applications like energy or mixing with polymers.’
Prof. García-Hernández is part of the team working on the EU’s Graphene Flagship, a 10-year, EUR 1 billion effort to enable graphene to move from a lab-based curiosity to a commercial product. She coordinates the ‘Materials’ section of the Flagship, which involves more than 20 research groups and aims to devise standard methods, called protocols, for making large quantities of graphene of various grades.
However, she says more applications are needed before it becomes clear which methods of production will become standard.
‘Graphene production is at this moment very adequate regarding the number of applications that we have already developed. In order to increase the production of graphene, we have to go first for the development of new applications that require that graphene; otherwise, there will be much more graphene in the market than is required.’
Pristine
The highest grades of graphene are reserved for electronic devices, which requires single-atom layers of pristine material on top of substrates, known as wafers. There is a lot of excitement about the potential for graphene in electronic devices such as sensors or light detectors, but this type of graphene is also the hardest to produce at a large scale.
Prof. García-Hernández says that because pure graphene layers are only one atom thick, it always needs to be packaged with other materials to be usable and this can alter its properties.
Currently, researchers are able to produce five four-inch wafers of high-quality graphene on a base of silicon carbide per day, and are on track to meet their target of eight wafers of three inches per day by 2016. However, there is still a long way to go to rival the millions of inches of silicon wafers produced each year.
“‘Graphene production is at this moment very adequate regarding the number of applications that we have already developed.’
Dr Ken Teo, director of nanoinstruments at German equipment manufacturer AIXTRON, who is also working on the Graphene Flagship, says that while device-grade graphene is potentially a high-value market, it will require a lot of development time before we see mass production.
The more immediate requirement is for mechanical grades of graphene, known as bulk graphene.
‘In its simplest form, bulk means powder, or powder dispersed in a liquid,’ said Dr Teo. ‘That’s the easiest to produce and that’s what we see today; there are many start-ups and also established companies producing bulk graphene.’
Such graphene is incorporated into plastics and has already found market applications in products such as tennis rackets and skis, where it adds strength, or on the soles of shoes, where it reduces electrostatic charge.
Between bulk graphene and device-grade graphene are coatings, which can be used to improve the corrosion resistance, conductivity or thermal properties of other materials. ‘The coating market usually comes after the bulk because there is a bit more functionality and it is a bit trickier to get the coating of the correct consistency and thickness,’ says Dr Teo.
The Graphene Flagship is currently devising standard tests to classify graphene. ‘We’re trying now to define how you characterise the number of layers, how you characterise the conductivity and other properties,’ said Dr Teo.
The aim is to get to a point where customers who use graphene can pick up a catalogue, look at the grade and know exactly what they are getting, in the same way as is done with aluminium or steel.
‘The producers manufacture graphene to meet that grade, and the end customers know what they’re getting when they buy that grade, and there’s clarity in the supply chain. So it makes the economic transaction much simpler.’
Conservative
One of the reasons that there is not yet a large demand for graphene-based materials is that many industries in which graphene could be used, such as the automobile and aerospace sectors, are inherently conservative.
‘These industries take time to penetrate,’ said Dr Teo. ‘We need to first qualify graphene in an application. Once it gets qualified there will be a true market demand for the material.’
In order to accelerate this process, Airbus is working as part of the Graphene Flagship to try and prove graphene’s worth in an application – in this case aerospace components.
This means demonstrating not only that graphene-based components pass industry tests, such as for lightning and bird strikes, but also that they perform significantly better than existing wings in order to replace the existing, tried-and-tested material.
‘A commercial company would never do that because it’s too risky at this early stage,’ said Dr Teo. ‘However, if the EU provides 50 % of the money, then commercial companies will be prepared to match the EU money to perform the work to see if it’s feasible.’
Over the coming years, researchers will be also be investigating how graphene can be used together with existing materials and processes to make the most of its properties without having to redesign and redevelop all the surrounding technologies.
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