That's a big slab of graphite. I can by using the scotch tape method peel pieces off

The way I think of it

Is that a single atomic layer of graphite is graphene. I knocked it around a bit this be?

Single molar mono layer by layer graphene where you've got two layers held together by these Van der Waals forces

That's got slightly different electrical properties and then you've got tri layer and when you get up to 50 layers the graphene starts looking black

It's you seem to note that

one model layer of graphene over a wide part of the electromagnetic spectrum

Absorbs about 2% of the light intensity

incident on it

So it's very transparent and that makes it an interesting material as well because you got a transparent conductor

Amazingly the absorbance of graphene is given by the fine-structure constant

Times pi. Now, if any of you up to sixty symbols, you know, I'm fascinated with the fine-structure constant

You could see a sixty symbols video on that Andrei Guymon costume Novoselov isolated

graphene from a lump of graphite and

For some electrical contacts on and so that had some very interesting

Electrical properties they made a little transistor out of it

What we're waiting for now is to make lots of transistors

Out to reverse a much more difficult job that it's very difficult to switch off the channel

because of a bit of quantum mechanics that the

Electrons in graphene of this curious band structure graphene does not have a bandgap

like silicon or germanium or gallium

Arsenide a band gap is a gap in energy

If you want to get the electrons flowing, you've got to put the Fermi energy which tells you the energy of

the energy of the highest energy electron

you

Don't want that in in the middle of in the middle of the gap because then you don't get any free electrons or free holes

So you guys are gonna push the chemical potential down into the valence band or up into the conduction band

they stand bandgap is crucial for being able to turn off your silicon or gallium arsenide field effect transistor because in the

band gap between the conduction band and the valence band

Any electronic state so you could get in there and you can't put them in there by putting in some impurities. Those states are

Evanescent they decay very rapidly in space. So the electrons can't propagate through it when you're in the conduction band

About above the bandgap of the valence band below the bandgap the electrons or the missing electrons call the hole called the holes

Can move very very freely and had pretty good velocities, especially in something like indium phosphide or gallium arsenite that's faster than silicon

But silica has got this fantastic property

You can oxidize its surface and make silicon oxide now in addition to that, of course in the latest bunch of transits

He's not using silicon oxide

As the barrier you want a higher dielectric material

So you got like a hafnium salts and oxides that can that can push up that and you get more more electrons in your channel

For a given gate voltage. What's so exciting about graphene from my kind of looking forwards point of view. Well whereas silicon

or germanium

Or indium phosphide or gallium arsenide has a structure like this

It's a very rigid structure

Basically, the diamond structure for silicon silicon is just like diamond except the silica is replacing the carbon atoms. It's a very rigid structure

And the electrons can move freely in all three direct dimensions

The surface for MOSFETs the interface between the silicon and the oxide or the hafnium oxide

At that surface

you've got to be very careful because once you break these bonds and you're changing the chemistry at the atomic level and

You can have charge on those on those surface States that charge can be very adverse in principle. You can scatter electrons

scattering electrons randomize your momentum

so if you're trying to get them to move down a channel with a high current as quickly as possible to make if you wanna

switch a device class off if they zigzagging and knocking off impurities and so on till

They take longer to go down the device their mobility as it says is reduced

So you want it's nice to have a clean surface now the point about graphene. Is that graphene?

This is a lump of graphite

It looks very black. Of course

But you could take graphite and thin it down by exfoliation

Using the scotch tape method and I I just did exfoliate a little bit of graphene

Earlier this surface underneath the sellotape. It's not beginning to look a bit dirty. And those are layers of

Multi-layer graphite it's not necessarily single layer graphite. They may be five six ten 20 layers, but amongst all that

There will be a single model layer of

Graphene, so having it thin that's really important

Well having it thin is is interesting from a physical point of view because now we've got the electrons moving in

a single mono layer and they move

first of all at a very high speed

About five times faster than they would in gallium arsenide or indium

Phosphide three of three to five times faster anyway at a 10 to the 6 meters per second

Which is actually one 300 through the speed of light curiously enough, which is pretty fast. The problem is

That things like silicon germanium gallium arsenide and so on

These have a energy gap between the conduction band and the valence band

Any electron in that gap which are many because there not many states in the gap those electrons tell you get stuck now with graphene

There's no energy gap. It's a problem for switching off a transistor. You can't you can't switch it off with a conventional potential so

What the Manchester group decided to do?

They decided to go vertical so by combining what you need to do is two switches current off

so this you make a vertical tunnel transistor and a key element of the vertical tunnel transistor is

By getting a sister material to graphi and colleagues agonal boron nitride

It's got exactly the same crystal structure as graphene except that alternate atoms

if all of these are carbon atoms in Boran light or this one it would be

Boron, this will be nitrogen. This will be boron

this will be the nitrogen and so on going around here and that creates a very very strong barrier very effective and

powerful barrier a barrier in fact at six electoral votes

so six times the value of the electron gap in the energy gap in in gallium arsenide and so

in this device the

Graphene layer has put on top of it boron nitride and then on top of that we have another

graphene layer and we mount that on silicon silicon oxide and use the silicon as a gate electrode and you use that to

Control the tunnel current through the layer and using that device we were able to make a transistor in which you could switch off

So we were very excited about that

That work was published in in science and we were even more surprised and pleased that six weeks off

I think six weeks after our paper came out the Samsung group came up with a very similar concept

And they managed to put about a hundred of these transistors on a chip

so I think at that point everybody thought wow, these vertical devices are gonna take off but

Things do seem to have that doesn't seem to have happened. I think the technology is very

Difficult we to remember that it took

You know many beers decades for silicon to go from just an interesting lab based material

Into a field effect transistor and then into these incredible integrated circuits with all these transistors on a single chip

It takes a lot of time and it takes understanding the physics and understanding the material science

but in parallel with with all this work on graphene, I want to emphasize the graphene is one of a large family of

similar

two-dimensional materials in which you clinics which can be

Exfoliated and there are about I believe it around the thousand of these

Materials and one material that we are working on here in Nottingham and Manchester interesting as well is indium selenide

Molybdenum disulphide is none materials

Remember your Mali slip used to probably put on the gears of your bicycle on the gear wheels

That's a similar material because the molybdenum disulphide sheets can slide over each other with almost no friction

So this isn't that very hot material as well

Now those materials have got an energy gap and an energy gap that depends on

the number of atoms you make the crystal out of the great thing about

These layered compounds. Is that when you break them apart you

Break the band of ours bonds

these these bonds

don't get charged don't trap and don't become defects it looks as if

You know

the electron just doesn't get scattered off that so that's that's an interesting aspect of these devices that people are playing around with and

indium selenide

This is again a

Manchester knot in collaboration

we produced a feel effect transistor that has some really very good very very nice properties and that

Was published a few years ago and people that that indium selenide 'sister coppers are making quite a big impact at the moment

people are working away on it because it's like gap semiconductor and

you can combine it you can switch it off with using a field effect and you can also put make or a nitride barriers and

Not only that but then take one band of ours crystal

And then it take another exfoliation one on top of it and make a multiple sandwich structure with lots of layers and bread and butter

and so on and

They're all sleeping between properties that these materials could have good ab, so could be the EM facility, but not no no, no

No silicon has got years to go heist

I quite like when I my PhD I was spent ages trying to put good electrical contacts on silicon

And eventually the French colleague put very good contacts on and we were a very nice paper on the electronic properties in bulk silicon

But that's forgotten in the history of silicon, but back in

1971-72

We looked at bonito photon resonance. Oh, I love silicon. I've got very got me interested in the field really and and curiously enough

I yes. I've almost forgotten this GC and Plessy were making very primitive

Feel effect transistors they were blimburn and reliable and we got our hands on some of these and we did some quite interesting

quantum experiments on the very first UK feel about transistors we couldn't get them from Germany or America, but

DC and Plessy were making material that materials. So no silicon is a great material. I'm not going to do it done

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