Published on Thursday May 14, 2009
Carbon nanotubes, or CNTs-the diameter of only a few millionths of a human hair- are favored in nanotechnology research and applications for their unusual properties. To be able to use CNTs to create ever smaller electronic devices, a nanotube would have to be furnished with multiple transistors. To achieve this goal, one has to be able to fabricate uniform, large-scale, controllable patterns on CNTs at a few tenths of a nanometer scale, a difficult task which to date has not been successfully addressed.
Drexel researchers, led by Professor Li, have now demonstrated that it is possible to create periodic, alternating patterns on carbon nanotubes with a period of 12 nanometers by decorating carbon nanotubes with judiciously selected crystalline block copolymers (in this case polyethylene-block-poly(ethylene oxide)). Block copolymers are comprised of two chemically different polymer chains that are covalently linked together at one end. The trick is to select two blocks of the copolymer so that one has a strong tendency to crystallize on the carbon nanotube surface and the other block can then be brought to the vicinity of the carbon nanotube. The period of the pattern can be easily controlled to be ~10-100 nanometers by simply varying the molecular weight of the block copolymers.
"The polymer and gold patterns on these nanotubes are exciting and raise intriguing possibilities for further research," says Dr. Andrew J. Lovinger, Polymers Program Director in the Division of Materials Research at NSF. "This is beautiful work by Professor Li demonstrating the potential of polymeric materials in the nanoworld."
From a technological standpoint, achieving an alternating pattern on an individual carbon nanotube at an ~10 nm scale is groundbreaking. By controlling the electrical conductivity of the areas occupied by each block, or domains, multiple transistors can be fabricated along the length of the nanotubes. The small domain size allows the possibility for hundreds of transistors to be fabricated on a 10-micrometer tube. Li has also demonstrated that even gold nanoparticles can be periodically immobilized along nanotubes, replicating the ordered block copolymer structure. This provides an excellent structure for single electron devices, devices that exploit the quantum effect of tunneling to control and measure the movement of single electrons.
"While there is a long road toward the commercialization of such technology," says Professor Li. "We have clearly demonstrated that we have the capability of controlling the pattern at approximately a 10-nanometer scale, with the precision and regularity on a single nanotube that could lead to extreme device miniaturization in the future. Our method is also generic and should be applicable to other one-dimensional nanostructures."
News on Professor Li's groundbreaking research can be founded at NSF; physorg.com; nanovip.com; Nanotechnology Now; and The Triangle, Drexel University's student newspaper.