Buckyballs form by shrink wrapping

The word ‘Buckyball’ may be part of common language, but so far there has been little understanding of how these nanoscale cages of carbon atoms form. Scientists at the Sandia National Laboratories and Rice University have now shown how it is done with the aid of a video and computer simulations.

Still images from a electron microscope video showing a giant fullerene shrinking inside a carbon nanotube, leaving a C60 molecule known as a Buckyball

Buckyballs are known to form at high temperatures, and the longstanding and popular ‘hot giant’ hypothesis suggests that their constituent carbon atoms first assemble by the thousands into flat graphite sheets. Heat distorts the sheets, effectively shrink wrapping them into smaller and smaller shapes, the most stable of which is the C60 Buckyball.

“This ‘hot evolution’ is so rapid that it was nearly impossible to prove or disprove it by experimental observation,” says Rice University materials scientist Boris Yakobson. “Sandia’s Jianyu Huang solved this problem by creating an ingenious, controllable heat bath inside a 10-nanometre-wide nanotube. That allowed him to capture video of giant fullerenes gradually shrinking.”

Huang’s video shows a giant fullerene molecule comprising around 2,000 carbon atoms shrinking, and it confirms predictions made by Yakobson’s team using detailed computer simulations.

“This vividly shows the shrink wrap process destroying a giant fullerene, and proposes a believable model for what is happening to the fullerene,” says Robert Curl, who in 1996 won a third share of the Nobel Prize in Chemistry for the discovery of Buckyballs. “I was thrilled to see this process postulated long ago by induction actually taking place before my eyes.”

The researchers say that it may be possible to exploit the findings to control the fullerene formation process, and tailor the particles for a variety of applications. “Carbon cages are extremely strong containers,” says Yakobson. “If we learn how to put stuff in, they can carry other substances such as radioactive isotopes for cancer treatment, or liquid dense hydrogen for energy storage applications.”

Further reading: Real Time Microscopy, Kinetics, and Mechanism of Giant Fullerene Evaporation, Huang et al., Phys. Rev. Lett. 99, 175503 (2007).

Figure: Still images from a electron microscope video showing a giant fullerene shrinking inside a carbon nanotube, leaving a C60 molecule known as a Buckyball. The scale bar is 10-nm wide (source: Jianyu Huang).

Article first published in Nanomaterials News.