Graphene: A Sandbox For Physicists, 1 Atom Thick
IRA FLATOW, host:
Earlier this week, two Russian scientists working in the U.K. got the Nobel Prize call, you know, the one that usually wakes them up in the morning, with the news that they had won this year's Nobel Prize in Physics for their work on a material called graphene.
It's a chicken-wire-shaped lattice of carbon atoms. It's similar to the stuff on your pencil, the graphite in there, but graphene is only one atom thick. It's the layer of only one atom thick.
So how do you peel off such a thin slice of carbon atoms? Well, these folks use Scotch Tape, believe it or not.
What's so special about thin pencil lead that it deserves the Nobel Prize? Joining me now to talk more about it is Joseph Stroscio. He is a fellow at the Center for Nano Science School and Technology at the National Institute of Standards and Technology in Gaithersburg, Maryland. Welcome to SCIENCE FRIDAY, Dr. Stroscio.
Dr. JOSEPH STROSCIO (Fellow, Center for Nanoscale Science and Technology, National Institute of Standards and Technology): Hi, Ira, it's a pleasure to be here with you today.
FLATOW: Thank you. Tell us what graphene this is a relatively new material, isn't it?
Dr. STROSCIO: Yes. Graphene was discovered 2004 by Geim and Novoselov, and graphene is essential a single atomic sheet of carbon atoms, as you described, and when you stack these sheets up, you get graphite, which was well-known before this. But no one really thought you could actually isolate a single sheet of the carbon atom.
FLATOW: Did they really do it using Scotch Tape?
Dr. STROSCIO: Yes, they did, and the way I can think of to describe it to you, it's something like: Have you ever played with phyllo dough when making baklava? You have these thin sheets of dough, which you have to peel from a stack, and then if the dough gets a little too sticky, you know, the sheets will break.
Instead of peeling it with their fingers, since graphene is so small, they used Scotch Tape, and when you touch the Scotch Tape to graphite and peel it off, and you look at the tape, you'll see like a sub-millimeter-thick layer of graphite on your tape.
But then you can repeat the process. You can take a clean piece of tape on top of that thin film and peel it off again, and you can continue repeating that process until you have exhausted all the layers in that thin piece, and you end up with single layers, double layers, triple layers of graphene on the tape.
Now the trick is to actually identify them, and they got lucky because they were interested in electric field effect. So they were naturally using these substrates, which consist of an oxidized wafer of silicon.
So they would put the graphene flakes from the Scotch Tape on top of this silicon oxide substrate, and if you look under an optical microscope, it turns out that the light waves have an interference effect between the graphene and the thickness of the silicon oxide, and that interference effect shows allows you to see a single layer in an optical microscope.
So if they didn't do that, if they used some other substrate, they would not have seen the graphene.
FLATOW: And this was worthy of a Nobel Prize?
Dr. STROSCIO: That in itself I don't think would have been enough. So the next step was the pass electrical current through the graphene. What they found was that the electrical transport properties was completely different from the past, you know, three decades of studies looking at electrical transport in these two-dimensional electrons.
FLATOW: All right, let me stop you there because it's really fascinating, the electrical and actually the heat properties, too, right, about what graphene can do. Our number, 1-800-989-8255 if you want to talk about graphene. You can tweet us, @scifri, @-S-C-I-F-R-I. So we'll talk more about this really incredible substance, graphene. Stay with us. We'll be right back.
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FLATOW: I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.
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FLATOW: You're listening to SCIENCE FRIDAY. I'm Ira Flatow. We're talking this hour about this year's Nobel Prize in Physics for graphene, a carbon substance called graphene, with my guest, Joseph Stroscio. He's a fellow, Center for Nanoscale Science and Technology at the National Institute of Standards and Technology in Gaithersburg, Maryland. Our number, 1-800-989-8255.
And Joe, when I interrupted you, you were telling us about the really unique properties of graphene, and one is that what happens when you put electricity.
Dr. STROSCIO: That's correct. So the electrons behave in graphene as if they have zero mass. And the thing that particles that typically have zero mass that you're familiar with are light waves. So the electrons in graphene behave as light waves and don't scatter the same way as electrons in regular materials.
And this gives them a very, like, large conductance. So they can travel in graphene much better than other materials. And the description of how electrons behave in graphene requires a new description of what we call a relativistic description of the electron system, and...
FLATOW: So it's basically not the way electrons travel on a piece of copper wire.
Dr. STROSCIO: That's correct.
FLATOW: It's a whole different thing. And is it more conductive than copper or even silver?
Dr. STROSCIO: It's about the same. You can achieve about the same conductivity, even though you have, you know, a single atomic sheet of carbon atoms.
Dr. STROSCIO: And the applications then come from having, you know, the flexibility of graphene. So you can think of it as almost like a Saran Wrap. You can, you know, stretch it. You can put it over any kind of substrate, and it will follow the contours and imperfections but still have complete connectivity with the electrical transport properties. So you can think of flexible displays.
FLATOW: Right, and it's very strong, too.
Dr. STROSCIO: Yes.
FLATOW: Right? How strong is graphene?
Dr. STROSCIO: Graphene is stronger than, you know, a piece of steel the same thickness. And this comes from the very short carbon-carbon bonds. So the carbon bonds in graphene are only 1.4 angstroms apart. And, you know, typically that's maybe, you know, in a metal system, you might have it would be a factor of two or more larger.
So because it's so tightly held together, that gives it its high strength.
FLATOW: I'd heard comparisons that you could take the weight of a car and balance a pencil on it and still not puncture through this sheet. Is that accurate?
Dr. STROSCIO: I haven't done that calculation.
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FLATOW: You might break the pencil.
Dr. STROSCIO: Yes.
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FLATOW: But it's still very, very strong.
Dr. STROSCIO: It's strong, yeah, for its size. So when you compare anything of that size scale, it wins out.
FLATOW: And how's it different than, say, a carbon nanotube.
Dr. STROSCIO: So it's essentially if you cut a carbon nanotube in half and roll it out, you have graphene. So graphene is essentially the basic building block of carbon nanotubes, of the buckyballs that you've covered on your show, and graphite itself. So graphene is essentially the basic building block.
FLATOW: And it also has a very good heat-conducting property.
Dr. STROSCIO: Right, it can transfer heat, you know, maybe 10, 20 times that of copper. So the combination of all these both the unique physics is what attracted, you know, scientists like myself, who are always trying to learn something new. And, you know, when we see new physics that we can learn, we are attracted to that.
But then combined with all the applications, you know, for transistors, replacing silicon in transistors, displays, chemical sensors, this is what drive the, you know, Geim and Novoselov to get the Nobel Prize.
FLATOW: Yeah, you know, I understand, and now I understand why. And it's such a short time. It's just a few years to get obviously isn't been you can see, just as we speak, how important this kind of discovery is.
And it makes me wonder: Why do you get the prize in physics when it sounds like we're talking about chemistry here?
Dr. STROSCIO: Well, I see it as physics, but...
(Soundbite of laughter)
Dr. STROSCIO: No, it spans all the disciplines. It spans physics, chemistry and material science, and that's probably another reason why it got the prize.
FLATOW: Let me get a call or two in here. John(ph) in Columbia, Maryland. Hi, John.
JOHN (Caller): Hello, how are you?
FLATOW: Hi there. Go ahead.
JOHN: Yes, my name's John Leto(ph), and I'm actually president of a company called Borbeck Materials(ph). And we (technical difficulties) world's first actually commercial applications of graphene. So (technical difficulties).
FLATOW: I think his cell phone has just dropped out.
Dr. STROSCIO: Yes.
FLATOW: He's making commercial, it sounds like commercial applications of graphene. I imagine there are going to be a lot of them, Joe.
Dr. STROSCIO: Yes, and, you know, probably one of the first ones are maybe composite materials where you, you know, you take this high-strength properties of graphene, and you mix it with plastics or other materials to both induce higher strength properties, but at the same time, you could also induce new electrical properties.
FLATOW: Let me go to another quick call, Greg(ph) in Louisville. Hi, Greg.
GREG (Caller): Hello, Ira. I enjoyed your performance on "The Big Bang Theory." I only just watched it just the other day.
FLATOW: Thank you.
GREG: Good show. Two quick questions. One is: Can this be used for supercomputers like to increase the speed of computers many times? It seems like it could be.
And also the second thing is: I wonder if this could be woven into cable for something like the space elevator. I know there's research being done like in Arthur C. Clarke's book "The Fountains of Paradise" - if you've ever read that from the '70s - but to actually build a space elevator from the equator, equatorial areas into space.
And what they're looking for with this is a much stronger carbon-based material, and maybe this is it, I'm hoping.
FLATOW: Yeah, we've thanks for calling, Greg. They kept talking about nanotubes not working. But would this be strong enough for a space elevator, or...?
Dr. STROSCIO: I don't know, but his first question was regarding high-speed applications, and that is one of the, one of the big niche areas for graphene. Because the electrons can move essentially unimpeded, because they have some unique quantum properties, the niche applications of high-speed transistors.
And in fact, you know, in the six years since the discovery, companies like IBM and other laboratories have demonstrated 100 gigahertz transistors already. And, you know, in the next, in the years to come, we'll probably those applications, will work in cell phones and things like that, where you'll need high frequencies.
FLATOW: How expensive is it to make and use graphene? Is it pretty cheap, or (unintelligible) get in on this?
Dr. STROSCIO: Well, if you make it yourself, it's cheap because you can just get graphite and do it yourself. If you want to buy it, it's expensive. So, you know, per gram, it's probably the most expensive element on the planet.
If you you know, there's a few companies that actually sell graphene for research applications.
FLATOW: A couple of more questions. Let's go to Bud(ph) in Nashville.
BUD (Caller): Hi.
FLATOW: Hi there.
BUD: I enjoy your show. You make science fun and interesting for laypeople, and it's a real service. Thank you.
FLATOW: Thank you.
BUD: Your guest I thought said something about it being a three-dimensional object, and I'm wondering if he could expand on that.
Dr. STROSCIO: So graphene is essentially in a planar system. So what we call that, it's two-dimensional. It doesn't have a third dimension. So the electrons are confined to that plane.
And when you confine electrons to a plane, new, you get new transport properties. And the first there was a Nobel Prize already awarded for that in 1985 for the quantum hall effect, and that was discovered in 1980 by von Klitzing, showing that when you confine electrons in a plane, you get completely new physical behavior.
And what graphene has done is shown that when it's in this particular hexagonal graphene lattice, you get a completely new physical electron transport property.
FLATOW: Let's see a call or two. Adam(ph) in Des Moines. Hi, Adam.
ADAM (Caller): Hello, great show.
FLATOW: Thank you, go ahead.
ADAM: My question is regarding, excuse me, graphene. It's I heard it could be used for touch screens and so forth. But considering the strength of it, could it be used for some sort of armor?
Dr. STROSCIO: Well, if you maybe make a composite material. I mean, one atomic layer thick, graphene itself is not, you know, it can be punctured easily. I mean, it's strong only relative to, you know, if you took steel and made it very thin, it's going to be stronger. But thin materials are still fragile.
So when but you could use it to enhance, you know, a material by mixing it with other materials.
FLATOW: Can you layer it like you would make plywood, you know, lots of layers and still hold its strength or its properties, or do they have to be separated?
Dr. STROSCIO: Well, actually, that's a good question. When you combine layers of graphene, you get different things. So another system that's very unique is two layers of graphene. When you put two layers of graphene together, we call that a bilayer system, and that, in itself, is completely different again, physical and electrical, from the single layer, and completely different from many stacks of graphene for graphite.
So you can get different electrical properties and different behavior, depending on how many layers you have.
FLATOW: And can you take other elements close to carbon and sort of do the same thing with them?
Dr. STROSCIO: So what - an area of research is to actually put elements in between the layers. So that's called intercalated graphite. And that was that's an area of study before even graphene was discovered. But you can you know, that alters a lot of the properties of the graphite by putting different elements in between.
FLATOW: Wow, it looks like there is just so much to learn still about this.
Dr. STROSCIO: Yes. And that's what fascinating to me and many other people is that, you know, we keep learning new things.
FLATOW: All right. Joe, thanks for taking time to be with us today. and I understand you're at a graphene conference. So...
Dr. STROSCIO: Yes. I'm at an electronic structure of graphene workshop right now at Princeton University, and here, we're trying to understand the nitty-gritty of how electrons behave in graphene. Because I mentioned you have to use these Dirac formulas to describe electron behavior in graphene, every time you look at it, you find something that you don't understand.
FLATOW: It's that quantum world, huh?
Dr. STROSCIO: Yeah. It's a quantum world. Yes.
FLATOW: All right. And now, I get it. Thanks for being with us, Joe.
Dr. STROSCIO: Oh, thank you.
FLATOW: Joseph Stroscio is a fellow at the Center for Nanoscale Science and Technology at the National Institute of Standards and Technology in Gaithersburg, Maryland.
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