Tag Archives: 2D

What is graphene and why all the hype?

There’s a decent chance you’ve heard of graphene. There are lots of big claims and grand promises made about it by scientists, technologists, and politicians. So what I thought I’d do is to go through some of these claims and almost ‘fact-check’ them so that the next time you hear about this “wonder material” you know what to make of it.

Let’s start at the beginning: what is graphene? It’s made out of carbon atoms arranged in a crystal. But what sets it apart from other crystals of carbon atoms is that it is only one atom thick (see the picture below). It’s not quite the thinnest thing that could ever exist because maybe you could make something similar using atoms that are smaller than carbon (for example, experimentalists can make certain types of helium in one layer), but given that carbon is the sixth smallest element, it’s really quite close!

phases-of-carbon

Diamond and graphite are also crystals made only of carbon, but they have a different arrangement of the carbon atoms, and this means they have very different properties.

So, what has been claimed about graphene?

Claim one: the “wonder material”

Graphene has some nice basic properties. It’s really strong and really flexible. It conducts electricity and heat really well. It simultaneously is almost transparent but absorbs light really strongly. It’s almost impermeable to gases. In fact, most of the proposals for applications of graphene in the Real World™ involve these physical and mechanical superlatives, not the electronic properties which in some ways are more interesting for a physicist.

For example, its conductivity and transparency mean that it could be the layer in a touch screen which senses where a finger or stylus is pressing. This could combine with its flexibility to make bendable (and wearable) electronics and displays. But for the moment, it’s “only” making current ideas work better, it doesn’t add any fundamentally new technology that we didn’t have before. If that’s your definition of a “wonder material” then okay, but personally I’m not quite convinced the label is merited.

Claim two: Silicon replacement

In the first few years after graphene was made, there was a lot of excitement that it might be used to replace silicon in microchips and make smaller, faster, more powerful computers. It fairly quickly became obvious that this wouldn’t happen. The reason for this is to do with how transistors work. That’s a subject that I want to write more about in the future, but roughly speaking, a transistor is a switch that has an ‘on’ state where electrical current can flow through it, and an ‘off’ state where it can’t. The problem with graphene is turning it off: Current would always flow through! So this one isn’t happening.

Graphene electronics might still be useful though. For example, when your phone transmits and receives data from the network, it has to convert the analogue signal in the radio waves from the mast into a digital signal that the phone can process. Graphene could be very good for this particular job.

Claim three: relativistic physics in the lab

This one is a bit more physicsy so takes a bit of explaining. In quantum mechanics, one of the most important pieces of information you can have is how the energy of a particle is related to its momentum. This is the ‘band structure’ that I wrote about before. In most cases, when electrons move around in crystals, their energy is proportional to their momentum squared. In special relativity there is a different relation: The energy is proportional to just the momentum, not to the square. For example, this is true for light or for neutrinos. One thing that researchers realized very early on about graphene is that electrons moving around on the hexagonal lattice had a ‘energy equals momentum’ band structure, just like in relativity. Therefore, the electrons in graphene behave a bit like neutrinos or photons. Some of the effects of this have been measured in experiments, so this is true.

Claim four: Technological revolution

One other big problem that has to be overcome is that graphene is currently very expensive to make. And the graphene that is made at industrial scale tends to be quite poor quality. This is an issue that engineers and chemists are working really hard at. Since I’m neither an engineer or a chemist I probably shouldn’t say too much about it. But what is definitely true is that the fabrication issues have to be solved before you’ll see technology with graphene inside it in high street stores. Still, these are clever people so there is every chance it will still happen.

Footnote

Near the top, I said graphene simultaneously absorbs a lot of light and is almost transparent. This makes no sense on the face of it!! So let me say what I mean. To be specific, a single layer of graphene absorbs about 2.3% of visible light that lands on it. Considering that graphene is only one layer of atoms, that seems like quite a lot. It’s certainly better than any other material that I know of. But at the same time, it means that it lets through about 97.7% of light, which also seems like a lot. I guess it’s just a question of perspective.

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