Carbon Structure Originated Chirality in Carbon Nanotubes

Monday, 29 May 2017: 08:00
Churchill B1 (Hilton New Orleans Riverside)
A. R. Harutyunyan (Honda Research Institute USA Inc), N. Pierce, and G. Chen (Honda Research Institute USA Inc.)
The origin of single wall carbon nanotube chirality includes fundamental understanding on formation mechanism of tubular carbon topology and its interrelations with catalyst features. Elucidation of this mechanism is key for realizing untapped potentials of nanotubes, because nanotube chirality governs its physical properties. For more than two decades studies have revealed the essential contributions of a catalyst features (diameter, morphology, composition and structure) in chirality abundance of grown nanotubes. Thus, chirality origination by catalyst structure via an epitaxial relationship emerges as a dominant mechanism. However, it is easy to overlook the hypothesis that was speculated in early stages of nanotube discovery in which chirality originates from hemispherical fullerene end-cap. To address this long standing dispute, our strategy was to decouple grown carbon structure properties from the impact of catalyst features. To this end, we grew carbon nanotubes on liquid catalyst with isotropic surface and thereby eliminated the entire complex catalyst feature’s contributions mentioned above. We found that the tubes with chirality (11,1)/χ=4.31o grown on isotropic surface of catalyst, can be up to eightfold preferable than tubes with larger helix angle (9,4)/χ=17.48o, although having exactly same diameter d=9.156Å. Abundances of tubes grown on solid polyhedral catalysts with certain structure and shape follow completely different patterns. This finding suggests chirality origination in carbon nanotubes as an intrinsic property of carbon structure. It distinguishes between the chirality origination by carbon structure and amendment by catalyst and could lead to the comprehensive theory of chirality formation. The role and energetics of carbon flux density and the type of elementary carbon building blocks (dimers, trimers, chains, clusters …) that form the precursor for carbon nanotube cap, and thereby originate the chirality will be discussed.