Fullerenes hit the small screen

Danish researchers film the growth of carbon nanofibres.

In spite of all the research on fullerenes and nanotubes, the process of making them has remained poorly understood. Now, for the first time, researchers in Denmark have succeeded in growing carbon nanofibres (multiwalled nanotubes) inside an electron microscope and recording a ’movie’ that shows how they grow.

Stig Helveg and his colleagues at the company Haldor Topsøe studied the deposition of carbon on a nickel nanocluster in an arrangement commonly used in the steam reforming process (where the growth of carbon fibres is an unwanted side reaction). By studying the process using in situ transmission electron microscopy, the researchers could observe in detail how the nickel cluster goes through a cycle of structural rearrangements. First it is wrapped up in cylindrical graphite sheets, which grow from the step edges of the metal particle. When the nickel has become a rod around four times longer than its width, it suddenly contracts to a compact shape. This sticks to the end of the now empty nanotubes and the cycle starts anew. For fibre growth to continue, it is important that the nickel surface remains in contact both with the gas phase and with the fibre.

The researchers recorded 16 different video sequences of these growth processes, with time resolution between two and 10 frames per second. Whether they show a general or a highly specific mechanism remains to be seen, however. As Pulickel M Ajayan warns in a commentary in Nature, the mechanism ’does not easily extend to smaller carbon nanotubes’.

Michael Gross