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Jagged edge

It's highly debatable whether these sharp-toothed ribbons will ever be put to use as blades for nanoscale saws. But the wonder is that they form at all. Made from semiconducting cadmium selenide (CdSe), they have one edge that is atomically smooth whereas the other traces out a sawtooth shape reminiscent of a graph of random noise.

These structures, just a few micrometres wide, are produced by evaporating CdSe powder in a furnace and using a flow of nitrogen to carry the vapour to a cooler region strewn with gold nanoparticles (C. Ma et al. J. Am. Chem. Soc. doi:10.1021/ja0395644; 2003). The gold particles act as catalysts for the regrowth of CdSe crystals as ribbon-shaped structures.

Ma et al. think that the asymmetry of the ribbon edges — one smooth, the other jagged — is caused by their differing chemical composition. The orientation of crystal planes in the ribbons means that their edges terminate in a layer of either cadmium or selenium. The former is more chemically reactive: in zinc oxide (which has the same crystal structure), a zinc-capped surface can act as a self-catalyst for further growth, resulting in comb-like structures (Z. L. Wang et al. Phys. Rev. Lett. 91, 185502; 2003). A similar process here at cadmium-terminated edges produces lateral growth with a rough profile, which resolves itself into the sawtooth profile.


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Ball, P. Jagged edge. Nature 427, 497 (2004).

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