New video showing the atom-by-atom growth of carbon nanotubes reveals they
rotate as they grow, much like the halting motion of a mechanical clock's second
hand. Published online this month by researchers at France's Université
Lyon1/CNRS and Houston's Rice
University, the research provides the first experimental evidence of how
individual carbon atoms are added to growing nanotubes.
"The key issue for realizing the potential of carbon nanotubes has always
been better control of their growth," said team lead Stephen Purcell of
the Université Lyon1/CNRS. "Our findings offer new insights for
better measurement, modeling and control of nanotube growth."
Carbon nanotubes are long, hollow cylinders of pure carbon. They are hair-like
in shape but are about 100,000 times smaller than human hair. They are also
about six times stronger than steel, conduct electricity as well as copper and
are almost impervious to radiation and chemical destruction. As a result, scientists
are keen to use them in superstrong, "smart" materials, but they need
to better understand how to produce them.
"The images from Dr. Purcell's lab show the atom-by-atom 'self assembly'
of a nanotube," said Rice co-author Boris Yakobson, professor in mechanical
engineering and materials science and of chemistry. "The video offers compelling
evidence of the rotational motion that accompanies nanotube growth. It brings
to mind Galileo's famous quote, 'And yet, it does turn.'"
In February, Yakobson offered a new theory suggesting that nanotubes grow like
tiny, woven tapestries, with new atoms attaching to twisting atomic threads.
The new video appears to support the theory, indicating that atoms are added
in pairs as the tube spins and grows.
To create the images, Purcell's team at LPMCN (Laboratoire de Physique de
la Matière Condensée et Nanostructures) used a field emission
microscope (FEM). A few atoms of metal catalyst were placed on the tip of the
FEM's needle-like probe, and carbon nanotubes grew atop the metal catalyst.
An electric current was passed lengthwise through the probe and nanotube, and
it projected a bright, top-down image of the nanotube onto a phosphor screen.
The bright spot was filmed by a video camera, which revealed the nanotube's
rotation during growth.
In one case, a nanotube turned approximately 180 times during its 11-minute
growth. A frame-by-frame analysis of the video showed that the rotation proceeded
in discrete steps -- much like the halting motion of the second hand on a mechanical
clock -- with about 24 steps per rotation.
"The results support our predictions of how nanotubes grow," Yakobson
said. "The video shows rotational movement during growth, as carbon atoms
are added in pairs to the twisting, chiral network of carbon atoms that comprise
Co-authors include Mickaël Marchand, Catherine Journet, Dominique Guillot
and Jean-Michel Benoit, all of Université Lyon. The research was supported
by the Programme en Nanosciences et Nanotechnologies of France's L'Agence Nationale
de Recherche, the National Science Foundation and the Air Force Research Laboratory.
here to watch the videos