Massimo Perucca, PhD - Diad Group: Nano-electro mechanical devices by assembly of nanotubes with same chirality

As-produced single-walled carbon nanotubes (SWCNTs) come in a mix of "chiralities" (or handedness) with varying electronic properties. However, the nanotubes all need to be of the same chirality if they are to be employed in device applications.  A team of researchers led by Ralph Krupke at the Karlsruhe Institute of Technology (Germany) may now have overcome this problem by using a "polymer wrapping" technique that produces arrays of tubes in which the carbon atoms are arranged in the same way. The devices might be used in high-performance electronics, sensing and nanoelectromechanical systems (NEMS). A SWCNT is a sheet of carbon just one atom thick that has been rolled up into a tube with a diameter of about 1 nm. The atoms in the sheet are arranged in a hexagonal  lattice and the relative orientation of the lattice to the axis of the tube (its chirality) determines whether the tube is a metal or a semiconductor. SWCNTs are ideal for use in a host of applications, such as sensors and transistors, thanks to their extremely high surface area and excellent charge transport properties but to make such devices, the tubes all need to be produced with the same chirality – something that is costly and difficult to achieve.

Ralph Krupke and colleagues have now obtained single-chirality nanotubes by using a polymer (poly(9,9-di-n-octylfluorenyl-2,7-diyl)), which selectively disperses certain SWCNT chiralities in solution. The sorted nanotubes are then assembled into arrays and devices are manufactured by use of dielectrophoresis  and by capacity coupling technique with application of specific bias. When applying the non uniform electric field, the dielectrophoretic force attracts the sorted nanotubes so that they deposit between the arrays electrodes, so bridging them to form devices.

The arrays consist of up to 90% of nanotubes with the same chirality, but researchers claim that reaching almost 100%  can be  possible  by improving the purity of the pre-sorting process. A large number of  nanotube devices have been characterized by  Raman and photoluminescence spectroscopy on a statistically basis and it was proven that the all the arrays have identical physical and electronic properties.

Further information available in: A. Vijayaraghavan, F.Hennrich, N. Stürzl, M. Engel, M. Ganzhorn, M. Oron-Carl, C.W. Marquardt, S.Dehm, S.Lebdkin, M.M.Kappes, R. Krupke
ACS Nano (2010), 10, 121