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But when they grow, basically these catalysts like iron,
carbon is somewhat soluble in these catalysts, okay?
So at these temperatures around 900 degrees is when you break
down your carbon source, like methane in this case, and
methane starts cracking, I think it cracks at like 980 or 950, so
usually you run between 890 and 950 here, so you start to crack
the methane, you get some free carbon, the carbon precipitates
onto this iron, preferentially, and these iron nano particles,
you have to use nanoparticles, right so these iron particles
are of the order of a few nanometers and the carbon forms
on either side and starts growing as a tube.
So it grows as a tube on the iron.
(female speaker). So will that shape then
determine the shape of the nanontube?
Like can the size of a nanoparticle determine
the size of a nanotube?
(Nadya). You know, I've not
been able to determine, it does to some
extent, it does to some extent, yes.
It does, but not fully, because these nanoparticles are actually
quite a bit bigger than the tubes, so the
tube is typically smaller than these.
So yes that's one thing, people have made bigger
nanoparticles and grown bigger tubes, or smaller when
they're growing smaller tubes.
There's a minimum diameter of the tubes, because at some point
you're bending, you get bending energies, so, It must be, it's
probably, 10, where's the, whoops, where's the nanotubes?
Anyway, so at some point, you bend, you can't bend things
enough that you actually form a defect right?
So it's probably 0.8 nanometers or something
is the minimum diameter of it.
And like I said, the particles are usually bigger than that, so
I'm not, they don't fully set at the size of it, but they do sort
of wed, and depending on something about the temperature
and the energy of the bonding right, they just
form and grow as tubes.
It's hard to know, I mean, for a while, there was a huge
controversy for years as to whether they grew, whether the
catalyst stayed where it was and the tubes grew above it, or
whether it grew underneath and now people think that the
catalyst stays at the top and it just continuously grows there.
It's actually, people didn't know this for a long time, so
it's still somewhat of an unknown process and not
entirely, you know.
So if you could grow graphene in an oven like this you would have
a billion papers right now.
So it's not so easy to do.
(female speaker). [unclear audio].
(Nadya). People don't usually
grow it, so they exfoliate it from graphite.
So you just buy graphite and scotch tape and
we put it on silicon.
Put it on silicon, silicon oxide.
Actually, the other thing about graphene is that the real key to
finding single layers was not just exfoliating it.
That's been done but it turns out that when you look at it
under a microscope and you have a 300 nanometer silicon oxide
layer under the graphene, you can actually see a difference
between one and two layers and more.
So if you don't have that, it's just some interference effect.
If you don't have that oxide layer, you just see lots and
lots of pieces of stuff and you have to do an AFM on all of them
to see the thickness and it's just impossible.
It too time-consuming, too many things.
But if you can actually optically see the graphene
candidates, then you can actually find it and manipulate
it and that was the big difference there.
It's sort of funny.
Usually it's on oxide.
You can only see it on these silicon oxide things.
Thanks.
[audience applause].
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