Portland, Ore. -- Carbon nanotubes are the strongest material on earth, more stable and rigid than diamond. But once that strength is fractured, nanotubes can be collapsed into sheets of diamond. The force that is released is enough to extrude even the strongest metals. By virtue of the controlled collapsing of metal-filled nanotubes, researchers at Rensselaer Polytechnic Institute (Troy, N.Y.) hope to harness the power of diamonds to machine nanoscale pins and posts for microelectromechanical systems.
"We were basically envisioning nanotechnology tools for extrusion/compression of nanostructured materials," said professor Pulickel Ajayan in RPI's Materials Science and Engineering department. "For example, if metals can be encapsulated into closed capsules, then it could act like a jig, which needs to be explored in more detail."
Jigs rely on precisely placed pins and posts to bend and form metal wires and other structures that create microelectromechanical systems (MEMS). The researchers believe they have discovered a way to create such metal-working tools at the nanoscale. Because nanotubes collapse with a force equal to that which forms diamond from graphite in nature, the researchers also believe that they have found a method of characterizing nanoscale materials.
"One could think of a lot of experiments where deformation at the nanoscale can be carried out with these tools inside electron microscopes to observe the atomic-scale deformation mechanisms in these nanostructures," said Ajayan. "This information is very important for developing structure-property correlations."
Ajayan performed the work with professor Florian Banhart of the Institute of Physical Chemistry at Johannes Gutenberg University (Mainz, Germany), and other researchers at Johannes Gutenberg University, the Institute for Scientific and Technological Research of San Luis Potosi, Mexico, and the University of Helsinki (Finland).
Ajayan and Banhart first discovered carbon's powerful forces in 1996 when they experimented with "super-fullerenes." Fullerenes, or buckyballs, are named for Buckminster Fuller, who invented the geodesic dome.
Subsequently, scientists speculated that the dome could be a template for a new form of carbon, which until then had been found only in diamond and graphite. But fullerenes proved to be another stable structure for carbon molecules. Officially carbon-60, the structure places 60 carbon atoms at the vertexes of a geodesic dome.
Ajayan and Banhart were experimenting with concentric carbon shells that began with a 60-atom core, but formed dozens of larger outer shells too. They found that by heating these super-fullerenes to 700°C and bombarding them with enough high-energy electrons, they could fracture the dome structures, collapsing them with enough force to nucleate pure diamond at their cores.
Next they want to harness these gigantic forces to study the precise placement of pins in jigs for fabricating future MEMS at the nanoscale. In their current experiment, they were able to create precisely tapered pins by extruding them from nanotubes that were collapsed by electron bombardment.