The Origin of Chirality in Carbon Nanotubes

The Origin of Chirality in Carbon Nanotubes



‚ÄčThe 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 hard 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 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. In contrast, for pair of tubes (19,3)/χ=7.2o and (17,6)/χ=14.5o with
exactly same diameter d=16.405 Å, the larger helix angle is preferable. Abundances of either
pairs of tubes grown on polyhedral catalysts with certain structure and shape follow completely
different patterns. This finding distinguishes between chirality origination from carbon structure
and adjustment by catalyst features and suggests that the chirality is an intrinsic property of the
grown carbon nanotube. Our results have immediate implication for understanding of chirality
formation and reconcile existing models for chiral specific growth of nanotubes by revealing the
contributions of various parameters. It also provides new strategy for achieving chirality specific
growth of carbon nanotubes.


CNT25 Symposium, Tokyo, Japan
28 Nov 2016
Neal Pierce, Gugang Chen, Nam Hawn Chou, Avetik Harutyunyan