Controlled synthesis of single-chirality carbon nanotubes

ROM 2014-12
Instrument: LT STM

Single Walled Carbon nanotubes (SWCNTs) are materials with extraordinary properties. They have received a significant attention during the past two decades because of their potential applications in numerous fields such as light detectors, photovoltaics, field effect transistors or sensors. Many of the SWCNTs properties depend sensitively on their structure, i.e. on the diameter and the arrangement of the carbon atoms in the lattice, which is characterized by the chiral index (n,m).
Electronic properties are particularly strongly affected with subtle structural changes switching tubes from metallic to semiconducting with various bandgaps. Therefore, in order to obtain SWCNTs with defined physical properties, it is necessary a synthesis technique to fabricate them with atomic precision. Monodisperse single-chirality (single (n,m) index) SWCNTs are thus needed to fully exploit their technological potential. Controlled synthesis of SWCNT (catalyst engineering, cloning strategies, tube sorting) have delivered SWCNT samples with narrow distributions of tube diameter and a large fraction of a predetermined tube type, but an effective pathway to truly monodisperse SWCNTs remains elusive.
The use of template molecules to unambiguously dictate the diameter and chirality of the resulting nanotube holds great promise in this regard, but has hitherto had only limited practical success. The results presented here show that this bottom-up strategy can produce targeted nanotubes. The synthesis methodology consist in the utilization of a molecule (P1) specifically designed to produce a (6,6) SWCNT cap that will be used as seed (S1).This step requires the complete dehydrogenation of the molecule (CDH). To achieve this purpose, P1 was deposited on a platinum surface (in this case Pt (111)). The annealing of the sample to 770K yields the complete dehydrogenation of the molecule, producing the required SWCNT seeds. We proved that those seeds can be elongated by exposing them to a carbon feedstock such as ethanol or ethylene at temperatures of 670 to 770 K. The elongation produces controlled single-chirality and essentially defect-free (6,6) SWCNTs with lengths up to a few hundred nanometers as revealed by STM and Raman.

Juan Ramon Sanchez-Valencia(1)†, Thomas Dienel(1), Oliver Gröning(1), Ivan Shorubalko(2), Andreas Mueller(3), Martin Jansen(3), Konstantin Amsharov(3), Pascal Ruffieux(1) and Roman Fasel(1,4)

(1) nanotech@surfaces Laboratoy, Empa, Swiss Federal Laboratories for Materials Science and Technology, Switzerland
(2) Laboratory for reliability Science and Technology, Empa, Swiss Federal Laboratories for Materials Science and Technology, Switzerland
(3) Max Planck Institute for Solid State Research, Germany
(4) Department of Chemistry and Biochemistry, Switzerland
† Nanotechnology on Surfaces Laboratory, Instituto de Ciencia de Materiales de Sevilla, Sevilla

Name and email of corresponding author
(1, †) Juan Ramon Sanchez-Valencia,