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Growing identical carbon nanotubes

Tailor-made organic precursors are the key to making atomically precise structures.

Single-walled carbon nanotubes (SWCNTs)—graphene sheets wrapped into hollow cylinders 0.5–2 nm in diameter—have inspired a vast range of proposed applications based on their many extraordinary properties (see, for example, the article by Phaedon Avouris, Physics Today, January 2009, page 34). But those properties depend on a SWCNT’s exact atomic structure, defined by its diameter and the angle between the tube’s axis and the graphene lattice vectors (see the article by Cees Dekker, Physics Today, May 1999, page 22). No method is known for creating bulk quantities of SWCNTs with identical structure. But Konstantin Amsharov (now at the University of Erlangen-Nuremberg in Germany), Roman Fasel (Swiss Federal Laboratories for Materials Science and Technology), and colleagues have now taken a big step toward that goal by synthesizing, for the first time, a small quantity of SWCNTs with a particular predefined structure. The result is a triumph for both organic chemistry and surface science. To start, the researchers implemented a 10-step chemical synthesis to create the precursor molecule shown at left in the figure. They deposited the precursors on a flat platinum surface and induced them to fold into the cap-shaped seed structure shown in the center. Then, using ethylene or ethanol gas as a source of new carbon atoms, they grew the seeds into longer SWCNTs, as shown at right. Raman spectroscopy and scanning tunneling microscopy imaging verified that the growing SWCNTs always adopted the structure of the seeds. The researchers are now working on scaling up their process to produce larger quantities and on developing precursors to other SWCNT structures. (J. R. Sanchez-Valencia et al., Nature 512, 61, 2014.)

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