All That Matters

This week some rather pessimistic articles on graphene’s commercial potential appeared in the UK press. On Tuesday, Aditya Chakrabortty commented in the Guardian on “How UK wonder substance graphene can’t and won’t benefit UK“, highlighting some pretty poor statistics when it comes to the innovation in graphene here in the UK, where Andrei Geim and Kostya Novoselov carried out their pioneering research:

Our record with graphene has been similarly dismal. Consultants calculate that China has taken out more than 2,200 patents on the material; the US more than 1,700; South Korea is closing in on 1,200. And the country that discovered it? Just over 50.

One of the problems, Geim is quoted in the article, is that there isn’t industrial sponsorship for his research:

Here is one of the world’s great scientists, pointing out that British businesses are either incapable or unwilling to use his inventions. The effect is rather like James Watt complaining that he can’t find any takers for his new steam engine.

This negative picture from a research perspective has been contrasted from the industrial side with a commentary by Jonathan Ely in the Financial Times this Saturday, saying there is too much investment into graphene: “The growing graphene investment bubble” (reading this link requires free registration at the FT). For Ely it seems the problem is not the industrial side – several companies now are on the market aiming to commercialize graphene – but that there is just nothing interesting about graphene (even though the Guardian continues to call it a ‘wonder’ material):

Graphene has been around since 2004, and many patents connected with it have been filed around the world (the Koreans are especially interested). Bill Gates has suggested it be used to make indestructible condoms to prevent the spread of disease in the developing world. But so far there are no widespread commercial uses for it.

How to consolidate these contrasting views? Perhaps the problem is that companies do not see the potential of graphene in the same way as Geim does. Graphene came from blue sky innovative research done by Geim and Novoselov, born more out of curiosity than because of commercial aspirations. Still, when the Nobel prize was awarded to these pioneers, commercial applications featured prominently in the comments of the Nobel Prize committee. This even caused me to call for caution on the technological potential. And it is fair to say that the promised broad-sweeping applications particularly based on graphene’s electronic properties have not yet materialized.

But this does not mean that all is bleak. […]

It’s been only a week ago that I wrote about the increasing competition for graphene. But as I said then, there are still some exciting advances based on graphene. An example is photonics, which is an area where traditionally graphene perhaps has not been as strong as in electronics. A reason for this is that being only a single atomic layer thin, graphene initially wasn’t expected to show much interaction with light. One of the more intriguing historic results in this area has been the fact that the absorption of light in graphene is determined by one of nature’s most fundamental numbers, the fine structure constant.

Plasmons in graphene can be created by illuminating the tip of an atomic force microscope (grey) with an infrared laser beam (red). Reprinted by permission from Macmillan Publishers Ltd. Fei Z. et al. Nature 487, 82–85 (2012). doi:10.1038/nature11253

But absorption of light is not where the true potential of graphene lies, namely on the nanoscale. On the same scale as electronic applications, because ultimately the aim is to achieve photonic functionality on a chip.

However, the control of light on the nanoscale typically requires surface plasmons. These are collective movements of electrons at the surface of metals. So in a sense surface plasmons function a bit like antenna that can focus light into tiny spots. […]

Move over graphene, there is competition in town. A new type of two-dimensional materials – with the far less appealing family name, transition metal dichalcogenides –  are increasingly gaining attention. Well, at least they’re giving it a shot. Graphene, a sheet of carbon atoms only one atomic layer thick, still has plenty going for itself in terms of electronic, optical and mechanical properties. There seems nothing that graphene can’t do.

On the other hand, there are also limits. When it comes to its electronic properties graphene is not a semiconductor in the same was as silicon is. It is lacking a bandgap, a gap in its electronic states that is important for light emitters and for some electronic devices.

Schematic model of transition metal dichalcogenide atomic layers. The yellow balls represent the chalcogenide atoms, the blue ones the transition metals. Reprinted by permission from Macmillan Publishers Ltd. Nature Nanotechnology (2012). doi:10.1038/nnano.2012.193

Transition metal dichalcogenides offer an advantage there. They are semiconductors, and they can have a bandgap. And as their name says, they are formed by a combination of chalcogens such as sulphur or selenium and transition metals such as molybdenum or tungsten. Typical examples are MoS₂ or MoSe₂. These materials have become such hot stuff now that their properties have been reviewed in this month’s issue of Nature Nanotechnology. And even though the field is still young, there is plenty to review. […]