Graphene is basically a single layer of graphite, a hexagonal array of carbon atoms extending over two dimensions endlessly. It's an atomic sheet of the same material that carbon nanotubes and graphite are made of. Graphite is many layers of this same material stacked on top of each other.
You can make it several ways; the simplest way is to simply peel it off a piece of graphite, which is an easy way but it is terribly uncontrolled. The other way, the way we do it, is to start with an electronic material called silicon carbide. If you heat it up, it's well known that the silicon leaves the surface and what?s left over reconstructs into graphene layers. In our case it could be as little as one and as many as several dozen layers of graphene.
The excitement actually started more than a decade ago, when people studied carbon nanotubes and saw that they had really great electronic properties. A whole community evolved out of that, looking specifically at the properties of carbon nanotubes. From that evolved the idea that maybe carbon nanotubes were only a specific form of graphene and that two-dimensional graphene might also be a useful electronic material. I thought that up in 2001 – that perhaps two-dimensional graphene, the basis of carbon nanotubes, could be used as an electronic material, and that's how our project started.
Originally, I had worked on carbon nanotubes myself for many years and looked at many of their properties. I was doing calculations on carbon nanotubes and, just as a lark, looked at what would happen if you didn't have a graphene tube, but a graphene ribbon. I found that many of the properties that carbon nanotubes have, on paper at least, were also there in graphene ribbons. That was a theoretical calculation, a very simple one; later on, it turned out that I was not the first one to make this calculation, but I realized that if we could make a two-dimensional graphene sheet and cut it in shapes, that we could have a new electronic material. So from 2001 until now we have been developing that idea and it has grown tremendously since then.
In the best case, graphene could do things that silicon will never do, so it would be a really valuable electronic material that could surpass silicon in many of its properties. It could have all of the properties that carbon nanotubes have, plus the added advantage that one can easily interconnect them and also convert the material from semiconductor to metal just by shape and relatively simple chemical doping techniques. We're actually in the process of developing a new electronic material, and we think that we have overcome the biggest hurdles that would stop carbon nanotube electronics while retaining the most essential features.
Carbon nanotubes have several problems: one, it is very difficult to put them exactly where you want to. Second, it's quite difficult to connect to them – to wire them up. Those are the two major hurdles with carbon nanotubes. Also, you don't treat them like you do silicon. When you do nanotube electronics, it's an entirely different set of processing steps that you use compared with silicon. If you work with graphitic materials – graphene – on the surface of silicon carbide, you can use all the common steps now used in the processing of silicon to make electronic devices, but on a much finer scale than what is possible with silicon. You can break the barrier that silicon is facing, going all the way down to the nanoscale, at which silicon breaks down; you can't use silicon when it's made that small for a whole variety of reasons. So you have all the advantages of graphitic materials, which are extremely robust and strong materials, and you avoid several of the disadvantages of silicon. That is really the main motivation for all of this. It piggybacks completely on the carbon nanotube electronics paradigm, but simply opens up the nanotubes – making them flat so that you can do things that you could never do with nanotubes.
From the very beginning, we knew that if this was going to make any sense at all that we should actually develop an electronic material. So the development of the ideas was two fold: one was the basic idea of using graphene for electronics, and the second was to look for the correct platform. That was critical because we really did not want to fall into the trappings of carbon nanotube electronics where the processing was so complex that it would be difficult to visualize how to make electronics. So we were heavily focused on working with a material that could be processed to actually make new electronic devices. It's more than just having the graphene material – it's actually having the platform and processing techniques that would be developed in parallel. That's what we're doing – we are developing at the same time the material, the processing methods, and the device structures. The team right now is very big, it includes many more people than the few that work in this laboratory; it has become an international collaboration. Again, it's basic science all the way to applications being developed in parallel.
Edited by James Palmer