h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Carbon nanotubes have the potential to be the next revolution in electronics, but there are major, show-stopping problems in making uniform samples with desired properties. Here's an idea I have to make uniform, controlled carbon nanotube samples.

It's well established that with almost any source of carbon, and a little heat, graphite will form on the surface of a transition metal single crystal surface in an ultra-high vacuum(UHV) chamber. You can even control the formation, by interrupting the reaction by quenching to liquid nitrogen (LN2) temperature. My idea is to start with a "seed" molecule, that has roughly the carbon nanotube shape, adsorb it onto a transition metal surface under UHV, then carry out the process to grow graphite. My idea is that the carbon atoms will add to the aromatic system of the seed molecule, and the sterics/shape of the seed will cause it to form the closed tube structure.

The seed molecule I'm thinking of would be the smallest possible unit of carbon nanotube. It would look like 2 crowns, fused together:

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If this worked, the growth should be very uniform (b/c of single xtal, UHV controlled conditions). ALso, it should be possible to dope the tubes, both homogenously and hetergenously (by changing the growth material from pure carbon to mixtures of Si/C, Ge/C, B/C, N/C...)

OK, it messed up my picture of the molecule. It was fine in preview, but not in the post. HEres another attempt.

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How about just adsorbing C60 onto the surface, then heating it util it bonds?

Also, what about bathing the adsorbate in UV light to activate new bond formation?

C60 was another idea a friend suggested. It's a good one too. I haven't looked in the literature yet about C60 adsorbing on a surface. I'm sure it adsorbs - the key is to get the chemical bonds to open. Maybe the UV light would be good for this. Another trick is one my Advisor came up with "collision induced adsorption". Adsorb the molecule on the surface. Smash an 80 kcal/mol neutral Xe atom into the molecule/surface. The energy can cause chemistry...

I've heard about x-rays and light inducing reactions - I just haven't heard or looked into it for graphite/aromatic formation. Could be a great idea

that should have read "I've heard about x-rays and light inducing reactions at surfaces" ... obviously light induces reactions in general. It's just less well understood/observed at surfaces under UHV.

When I was working on phthalocyanines, I built a furnace for purifying them, which was a glass tube in a temperature gradient. One simply put the Pc in at the hot end, and passed an inert gas stream over the substance. The Pc and impurities sublimed at different temperatures and formed bands of material.

Now, I thought that if one replaced the Pc with a carbon arc, the fullerene type molecules would get carried down the stream and subllime out. If one could activate bond breakage/reformation at certain zones in the tube, then one might be able to grow nanotubes in significant quantities

I see what you're saying, I think. Perhaps via a laser of UV lamp, focused on a section of the tube where you know that you're condenscing the desired starting material, you would induce the nanotube formation?

How about a He flow through the tube, and inducing an electrical discharge?

Are you still using the Pc as your starting material? Then using the He flow to carry it through the tube, with the electrical discharge occuring at a certain position downstream from the starting material?

Oh God, no. That was over 10 years ago! Anyhow, Pc's are pretty indestructible: that's why they make such good pigments.

People (here on the third floor) are using molecular sieves (3 or so nm diameter) as a cast form to make multi-wall CNTs...

HELL

that's cool. I thought the pores weren't straight in the sieves...maybve they are? Or isn't it a problem? Or are they getting shorties?

The thingus is called MCM-41, it's baiscally glass with cylindrical holes (ranging from 2-4nm) arranged hexagonally. They grow it on a metal surface, which acts as a sortofa catalyst for the CNTs. Electron micrographs show the entire thing, after the CNT synthesis, looks like a small surface with pots and long hair (the CNTs) growing out of it. The CNTs are quite long, µm-size IIRC. The big drawback is that they have not figured out everything about the mechanisms (synthesis condistions and so on) yet. The CNTs are not very uniform, different wall strength (unfortunately no sw-CNTs), different wrap-around planes, n'stuff... But it's nice having nano-sushi from those porous molecular sieves anyways. It's also (IMO) more efficient than the usual voodoo.

HELL