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Exploring the origin of chiralty in carbon nanotubes

(Nanowerk News) The tremendous potential of carbon nanotubes is hindered by one key factor: nanotube properties are delicately reliant on their chirality, and yet there is no established technology for chiral selective production. The root of the challenge is deeply fundamental: understanding the origin of chirality.
In a paper in ACS Nano ("Intrinsic Chirality Origination in Carbon Nanotubes"), researchers study chirality abundances of carbon nanotubes grown on floating liquid gallium droplets, which excludes the influence of catalyst features, and compared them with abundances grown on solid ruthenium nanoparticles.
The observed results of growth on liquid droplets bolsters the intrinsic preference of carbon nuclei toward certain chiralities.
Schematic of the reactor for growth of single-walled carbon nanotubes on floating catalysts
Schematic of the reactor for growth of single-walled carbon nanotubes on floating catalysts. (© ACS)
As the team reports, for nanotubes grown on liquid catalyst droplets, nucleation kinetics can create chiral preference even for tubes with exactly the same diameter and similar nucleation energy barriers, despite a large variety of possible nuclei.
The scientists observe that preference toward certain chirality can be predicted by knowing the critical nuclei size, Zeldovich factor, and the number of atoms in a given carbon nuclei. Consequently, controlling these parameters can lead to chirality preferable growth of the tubes.
"We expect that revealed dualism in nanotube chirality origination would help to create a comprehensive theory of nucleation and growth by considering the role of nucleation kinetics in chirality distribution," the authors conclude their report. "It can ignite a strategy to achieve chiral selective/preferential growth based on liquid catalyst droplets, since unlike solid catalysts, in the case of a liquid catalyst, the number of variables are dramatically reduced."
This method implies that thorough control of catalyst diameter is critical, although this requirement is common among all reported methods aiming at chirality-controlled growth.
The authors believe that the exploitation of colloidal Ga clusters with predetermined dimeter (smaller is preferable) and narrow diameter distribution could be an effective approach. This method in combination with low-temperature and/or high-pressure synthesis conditions may lead to selective/preferential growth.
By Michael is author of two books by the Royal Society of Chemistry: Nano-Society: Pushing the Boundaries of Technology and Nanotechnology: The Future is Tiny.
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