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Buckyballs were discovered at Rice in 1985, but understanding the
intimate details their formation has vexed scientists. Buckyballs form
at high temperatures, and one long-standing theory of their genesis is
the "hot giant" hypothesis, which suggests that the carbon atoms first
assemble by the thousands in flat graphite sheets. Heat distorts the
sheets, "shrink wrapping" them into ever-smaller shapes, and
buckyballs survive thanks to their perfect symmetry.
"This 'hot evolution' is so rapid that it was nearly impossible to
prove or disprove it by experimental observation," said study
co-author Boris Yakobson, professor of mechanical engineering and
materials science at Rice. "Sandia's Jianyu Huang solved this problem
by creating an ingenious, controllable heat bath inside a
10-nanometer-wide nanotube. That allowed him to capture video of giant
fullerenes gradually shrinking."
Huang, who performed the experiments while at Boston College and
analyzed the data at Sandia, said the results constitute the first
experimental evidence for the 'shrink-wrapping' and 'hot-giant'
fullerene birth mechanisms.
Huang captured the high-resolution images using a transmission
electron microscope (TEM). The video shows a large fullerene, with an
estimated 2,000 atoms of carbon gradually shrinking. It confirmed
predictions about the atomic mechanisms that Yakobson's team at Rice
had made based on detailed computer simulations.
"If heat is sustained, as it was when we took these images, the
fullerenes undergo a further shrinking and vanish," Huang said. "This
confirms an aspect of 'shrink wrapping' theory that was predicted by
Rice's Rick Smalley and Bob Curl made shortly after they discovered
fullerenes."
Huang and Yakobson said it may be possible to exploit the findings to
control the fullerene formation process and tailor fullerenes for a
variety of applications.
Co-authors of the research include research scientist Feng Ding and
graduate student Kun Jiao, both of Rice. The research was funded by
the Office of Naval Research and the Department of Energy's Center for
Integrated Nanotechnologies.
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