What's the smallest material we can build with?

27 March 2018

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Question

What's the smallest material we can build things with?

Answer

Chris Smith put this question from listener Janet to material scientist Rachel Oliver, from Cambridge University. 

Rachel - Well the smallest building block of any material is an atom and I guess that’s the smallest thing you can build things with. You hear about splitting the atom; it’s totally true you can split an atom. But if you have a brick which is something you’re used to building things with and you split that brick, you kind of get two small bricks. If you split an atom into two pieces, it’s like splitting and brick and ending up with say two balls of cotton wool or something, you end up with something completely different.

So our smallest building block of material is a single atom and people do build things with single atoms. There are technologies whereby you can take a tiny tiny needle, really really sharp and essentially use it to push materials around. There’s some guys at IBM in the US, and they use single atoms on surfaces to build what they call quantum corrals. Now a corral, I guess is in old west terms is basically like a fence, so they build a fence out of atoms on a surface and you can actually look at pictures of them with every atom in a circle. They’re not enclosing little tiny cows, like a corral would have done in the old west, they’re enclosing electrons, which are negatively charged particles and then looking at how the electrons behave in that little fence they’ve built.

Chris - Why is it useful to be able to fiddle with atoms like this though? Is this actually going to help us in the future if we can engineer atoms in this way?

Rachel - Potentially. Everybody uses, I’m sure, laptops and tablet computers and all this kind of thing, and those computers have been getting smaller, and smaller, and smaller, and as they get smaller and smaller they get faster and faster. The reason the computing companies like IBM, Intel, anybody like that are really interested in building with atoms is they’re pushing the size of these little switches inside computers right down to the atomic scale; it’s a tough thing to do though. But there are, even now, companies out there who are developing industrial scale technologies building at the atomic scale.

Chris - Is it also relevant that - I think it was Chris McManus - who came on this programme; he wrote the book about being right and left handed and said that “asymmetry begets asymmetry”, so if you want to build something asymmetric you start with particles themselves that are asymmetric. So if you want to build a really strong component for a jet engine then you have to start with the right things in the right configuration down at the atomic scale so that you get something on the big scale that has those properties, it’s just amplified up to a big scale that we can see.

Rachel - Yeah. In terms of things like a jet engine you need exactly the right ingredients, but the metals that are used in jet engines they’re the important length scale there is very very tiny so down at what I would call the nanometre scale. People might be more happy in millimetres and a nanometre is like a millionth of a millimetre, and you have to engineer the structure of that material right down at that scale in order for the jet engines to work. The thing that’s tough about jet engines is that they have to keep working at really really high temperatures, and you can’t let the material get longer, expand by even very very small fractions at those high temperatures otherwise the blades of the jet engine will start bumping into the casing and the aeroplane goes slightly bang, which is not really what you want.

Chris - The claim that’s made by companies that make and engineer these jet engines is that the gas stream that’s running through the middle of that engine is about 1500 degrees centigrade. And the materials that the engine itself is made of will melt at less than that temperature so you’re actually containing and constraining and using a gas stream that’s at more than the melting temperature of the thing you’ve made your engine from and you have to engineer it to withstand that, which is just phenomenal work really, isn’t it?

Rachel - Yeah, it’s amazing. And there are different ways that materials can deform and expand and change shape, and some of those we have to worry about at normal room temperature, but some of them only start when you get close to the melting temperature. So that means that you have to really be very clever about how you engineer stretches right up at those very high temperature.

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