How Nanotubes Grow: A theory that has nothing to do with reality

Tubes, spirals, rings,
and decorative loose ends

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From “Controversial new theory for nanotube growth”,
a news article about the paper
“Dislocation theory of chirality-controlled nanotube growth”
F Ding, AR Harutyunyanb, and BI Yakobson, Proceedings of the National Academy of Sciences (USA),
PNAS Early Edition, 6 Feb 2009.

Today I read a report of a controversy about the growth of carbon nanotubes. There’s an entirely bogus theory involved, two scientists using harsh words, and another scientist taking the hit. Behind the controversy is another theory that I think is almost certainly correct. The real story, though, is in the reporting itself. [See update below — the information flow had other currents, too.]

The story starts with a theory of carbon nanotube growth presented by Boris Yakobson and his colleagues in a recent PNAS paper. The central actor of the story is a (nonexistent) theory suggested by the correct, vivid, and potentially misleading diagram to the right. The result is a news report titled “Controversial new theory for nanotube growth” presented in Chemistry World, a news publication of Britain’s Royal Society of Chemistry.

Nanotube growth: From reality to unreal theory

First, some background to the science: In most nanotubes (the chiral kinds) the rows of atoms form spirals, and the ends of the spirals inevitably make an open tube-end jagged; it can’t form a smooth ring. In their PNAS paper, Boris Yakobson and his colleagues propose that as nanotubes grow, new carbon atoms are added at the end of these spirals. This makes a lot of sense, because it parallels the way that crystals usually grow. I find it hard to imagine that they are wrong about this, and the paper shows evidence that, under a wide range of growth conditions, tubes with more steps (more growth points) grow proportionately faster. A nice result.

Why, then, do we find two other nanotube researchers (Nicole Grobert and David Tománek) quoted in Chemistry World as saying that Yakobson’s theory “has nothing to do with reality”, and that it “contradicts common sense”? These are strong words. Has Yakobson in fact lost his common sense, setting him adrift in unreality, perhaps on the verge of claiming that nanotubes are knitted from yarn by elves with tiny fingers? Inquiring minds want to know!

Elf-theories from the Land Beyond Science

The key to the mystery is close at hand: The reporter quotes Tománek as saying that the theory contradicts common sense “in claiming that a couple of yarns, representing monoatomic carbon chains, should nicely attach to each other to form a hollow tube”. Now we can be pretty sure what the reporter told what was somehow communicated to Grobert and Tománek, before they had an opportunity to read the Yakobson paper — she told them that the information led them to believe that Yakobson had proposed what amounted to an elf-theory.

Tománek and Grobert were right: The preformed-strand theory violates scientific common sense and has nothing to do with reality. But the theory had nothing to do with the paper, either, it was an intrusion from from the land beyond science, masquerading as a scientist’s opinion.

[In the following, the small-yet-consequential failings I attributed to “the reporter” should be attributed in a more diffuse and ambiguous way.] The reporter [?] misunderstood the actual theory in seemingly a small way, thinking that carbon atoms form strands before binding to the tube (as the diagram above inadvertently suggests), when in fact, carbon atoms link into rows directly, as part of the tube itself. From a scientist’s perspective, though, this “small” misunderstanding is enormous. It makes the difference between a theory that is almost obvious when explained, and a silly idea that no competent scientist would entertain for more than an instant. (I’m reminded of the small-yet-enormous misunderstanding about atomically precise fabrication, the mistaken idea that it implies picking up and putting down individual atoms, when positioning and orienting reactive molecules is quite sufficient, and often done today by enzymes.)

I assume that this elvish media mischief has done little damage to anyone’s reputation. The problem is in a single press report, not a thousand, no one is in the wrong (even the reporter is excusable), and I would guess that Grobert and Tománek find the article as embarrassing as Yakobson does. Besides, in a case of confusion like this, anyone can read the original PNAS paper and see that there are no elf-fingers in the theory, just a description of how known phenomena can combine to produce orderly arrangements of atoms. (The link to the Yakobson PNAS paper is above, in the first paragraph.)

24 February update: The reporter wrote to tell me that part of the information flow to the scientists was more direct, through a press release — part of the reporting process, but none of her doing. She quite properly emphasizes that the body of the article contains a clear and accurate statement of Yakobson‘s theory, free of any misunderstanding. These added facts nicely round out a picture of the ambiguity and systemic nature of this sort of problem, in which well-motivated explanations and metaphors mutate, somewhere in the chain of human communication, into misunderstandings of what was originally mean, with harsh judgments following — and no one at fault.

Tagged as: nanomaterials, Nanoscience, Nanotechnology