Bombarding a carbon nanotube with electrons causes it to collapse with such
incredible force that it can squeeze out even the hardest of materials, much
like a tube of toothpaste, according to an international team of scientists.
Reporting in the May 26 issue of the journal Science, the researchers suggest
that carbon nanotubes can act as minuscule metalworking tools, offering the
ability to process materials as in a nanoscale jig or extruder.
use a variety of tools to manipulate and process
metals. For example, handy "jigs" control
the motion of tools, and extruders push or draw materials
through molds to create long objects of a fixed diameter.
The newly reported findings suggest that nanotubes
could perform similar functions at the scale of atoms
and molecules, the researchers say.
The results also demonstrate the impressive strength
of carbon nanotubes against internal pressure, which
could make them ideal structures for nanoscale hydraulics
and cylinders. In the experiments, nanotubes withstood
pressures as high as 40 gigapascals, just an order
of magnitude below the roughly 350 gigapascals of pressure
at the center of the Earth.
"Researchers will need a wide range of tools to
manipulate structures at the nanoscale, and this
could be one of them," says Pulickel Ajayan, the
Henry Burlage Professor of Materials Science and
Engineering at Rensselaer and an author of the paper. "For
the time being our work is focused at the level
of basic research, but certainly this could be
part of the nanotechnology tool set in the future."
The current paper is the latest result from Ajayan's
longtime collaboration with researchers at Johannes
Gutenberg University in Mainz, Germany; the Institute
for Scientific and Technological Research (IPICyT)
of San Luis Potosi, Mexico; and the University of
Helsinki in Finland. Florian Banhart of the Institute
of Physical Chemistry at Johannes Gutenberg University
is the lead corresponding author of the May 26 Science
Carbon nanotubes have been hailed as some of the
lightest, strongest materials ever made, and they
are beginning to find use in a wide variety of materials.
Yet while many of their distinctive properties have
been studied in detail, the strength of carbon nanotubes
against large internal pressures has yet to be fully
explored, according to the researchers.
research builds on the team's earlier findings
detailing how bombarding electrons at carbon "onions" --
tiny, multilayered balls of carbon -- essentially
knocks the carbon atoms out of their lattice.
Surface tension then causes the balls to contract with
great force, which allows carbon onions to act as high-pressure
cells for creating diamonds.
In the new report, the team discovered that the
same thing happens with nanotubes, producing enough
pressure to deform, extrude, and even break solid
materials that are encapsulated within.
The researchers filled carbon nanotubes with nanowires
made from two extremely hard materials: iron and iron
carbide. When irradiated with an electron beam, the
collapsing nanotubes squeezed the materials through
the hollow core along the tube axis, as in an extrusion
process. In one test, the diameter of iron carbide
wire decreased from 9 nanometers to 2 nanometers as
it moved through the tube, only to be pinched off when
the nanotube finally collapsed.
These jigs could be perfect nanoscale laboratories
to study the effects of deformation in nanostructures
by observing them directly in an electron microscope,
the authors suggest. An electron microscope from
Johannes Gutenberg University was used for the experiment,
which allowed the researchers to watch the extrusion
process proceed in real-time at high resolution.
Ajayan received funding for the project from a National
Science Foundation Division of Materials Research
grant to facilitate inter-American collaboration
between Rensselaer and the group at IPICyT, which
is headed by Mauricio Terrones, another lead author
of the paper.
Nanotechnology at Rensselaer
In September 2001, the National Science Foundation selected Rensselaer as one
of the six original sites for a new Nanoscale Science and Engineering Center
(NSEC). As part of the U.S. National Nanotechnology Initiative, the program
is housed within the Rensselaer Nanotechnology Center and forms a partnership
between Rensselaer, the University of Illinois at Urbana-Champaign, and Los
Alamos National Laboratory. The mission of Rensselaer's Center for Directed
Assembly of Nanostructures is to integrate research, education, and technology
dissemination, and to serve as a national resource for fundamental knowledge
in directed assembly of nanostructures. The five other original NSECs are
located at Harvard University, Columbia University, Cornell University, Northwestern
University, and Rice University.
Rensselaer Polytechnic Institute, founded in 1824, is the nation's oldest technological
university. The university offers bachelor's, master's, and doctoral degrees
in engineering, the sciences, information technology, architecture, management,
and the humanities and social sciences. Institute programs serve undergraduates,
graduate students, and working professionals around the world. Rensselaer
faculty are known for pre-eminence in research conducted in a wide range
of fields, with particular emphasis in biotechnology, nanotechnology, information
technology, and the media arts and technology. The Institute is well known
for its success in the transfer of technology from the laboratory to the
marketplace so that new discoveries and inventions benefit human life, protect
the environment, and strengthen economic development.