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  • Graphene: everybody's talking about it. When hearing some of its basic properties, you

  • might have wondered if people were confusing it with some kind of substance only found

  • in comic books. It's one atom thick, conducts electricity better than silver, conducts heat

  • better than diamond, and it's stronger than steel. It would take the focused force of

  • an elephant balancing on a pencil point to pierce through a piece of graphene as thick

  • as plastic wrap.

  • And yet, graphITE is made of the same stuff. And yeah, that crumbly stuff used to make

  • your pencil is a lot less impressive. So what's up? Graphene is made of carbon, and carbon

  • has only two naturally occurring crystalline structures; graphite, which is just stacks

  • and stacks of graphene piled on top of each other, and diamond, which is a network of

  • carbon atoms arranged into tetrahedrons one after the other. For being composed of entirely

  • the same element, those two things don't seem to have a lot in common. Diamond is clear,

  • graphite is black. Diamond is a nearly-perfect electrical insulator, while graphite is both

  • a great conductor of heat and electricity.

  • The differences between these substances all come down to the arrangement of their atoms.

  • Carbon has four outer electrons. In diamond, all four of those electrons bond to carbon

  • atoms around it, forming those tetrahedrons. This makes for an extremely rigid and strong

  • crystal. It's an insulator, because there are no electrons left over to carry a current,

  • and it's clear because light can't easily excite electrons that are tied up in such

  • stable bonds, which is where they'd otherwise be absorbed. Graphite, on the other hand,

  • is a crystalline form of carbon in which each atom is only bonded to three other carbon

  • atoms. Those atoms form a two-dimensional sheet of hexagons in which each atom has one

  • unpaired electron left over. And those electrons will go flying across the matrix of atoms

  • if you apply an electric current, allowing it to readily conduct electricity. They also

  • gobble up any photons coming their way, which is why graphite is black.

  • But while graphite is a great conductor, its natural form consists of layers of those sheets.

  • So if a current is applied to it, those free electrons have lots of different directions

  • they can go in, taking tangents up and down and left and right and so on. But if you strip

  • away just a single layer, forming graphene, then you have what amounts to an electron

  • super highway, a flat matrix of carbon atoms for that current to fly across. And those

  • sheets of carbon are pretty easy to separate because they're not molecularly bonded to

  • each other. That's why graphite is so soft. Instead, they're held together by Van Der

  • Waal's bonds, kind of a weak, electrostatic bond that's the same force that makes sticky

  • tape sticky. And in fact, graphene was only discovered in 2004 when two physicists at

  • the University of Manchester, Andre Geim and Konstantin Novoselov, decided to use sticky

  • tape to peel off thinner and thinner layers from a slab of graphite. Eventually, they

  • got a layer just one atom thick.

  • So that's what it is, but what is it good for? Because of its terrific conductive properties,

  • scientists are excited by the possibility of using graphene as the replacement for silicon

  • in microchips. Not only can electrons move faster across graphene, they're also subjected

  • to less noise. That means the electron can move from one side of the sheet to the other

  • in a straight line without detouring around a whole lot of atomic potholes. Scientists

  • think that graphene transistors could operate at frequencies of up to a thousand gigahertz.

  • That's ten times the maximum of silicon.

  • Another proposed use of graphene is in touch screens. The topmost layer of a touchscreen

  • has to be an excellent conductor of electricity, so the device can sense your fingertip. The

  • material we use now is indium tin oxide, but it's both rare and brittle. Even ground into

  • powder, graphene retains many of it's extraordinary properties, so it could replace graphite or

  • other forms of carbon in anything from car tires to double-A batteries to make them stronger

  • or more conductive.

  • The biggest problem with graphene though is how hard it is to make. I mean, peeing off

  • a tiny sheet at a time with sticky tape isn't really scaleable. We can grow graphene sheets

  • by hitting up a sheet of hydrocarbons like methane until the hydrogen separates, leaving

  • only the carbon behind, but the graphene we get from this is mostly low quality.

  • Basically, it's hard to create a one atom thick sheet of anything. And it's also really

  • hard to get a completely pure sample of anything, and here we're trying to do both. But then

  • again, the silicon industry faced the same purity problem fifty years ago, and we eventually

  • solved that problem with time and some money. So in some more time, and some more money,

  • I'm sure we'll do the same thing for graphene.

  • Thanks for watching this SciShow dose. If you'd like to help us keep exploring the frontiers

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グラフェン:次の大きな(しかし薄い)もの (Graphene: The Next Big (But Thin) Thing)

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    李顯章 に公開 2021 年 01 月 14 日
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