Why nanotubes grow chiral

Abstract

Carbon nanotubes hold enormous technological promise. It can only be harnessed if one controls their chirality, the feature of the tubular carbon topology that governs all the properties of nanotubes-electronic, optical, mechanical. Experiments in catalytic growth over the last decade have repeatedly revealed a puzzling strong preference towards minimally chiral (near-armchair) tubes, challenging any existing hypotheses and making chirality control ever more tantalizing, yet leaving its understanding elusive. Here we combine the nanotube/ catalyst interface thermodynamics with the kinetic growth theory to show that the unusual near-armchair peaks emerge from the two antagonistic trends at the interface: energetic preference towards achiral versus the faster growth kinetics of chiral nanotubes. This narrow distribution is inherently related to the peaked behaviour of a simple function, xe À x .

Chirality analysis of horizontally aligned single-walled carbon nanotubes: decoupling populations and lengths

“…19,20 The measured abundance of SWCNTs with a given chirality is determined by taking the product of the population and average length of each specic type. 18 Despite these efforts, an experimental analysis of the detailed chirality distribution is still required to obtain an improved understanding of chirality-controlled growth. In contrast, the screw dislocation model suggests that chiral SWCNTs with larger chiral angles have higher growth rates, 17 resulting in longer average lengths for near-armchair SWCNTs.…”

In situ tracking of defect healing and purification of single-wall carbon nanotubes with laser radiation by time-resolved Raman spectroscopy

“…Considering near-armchair tubes are more thermodynamically favourable and predominantly produced, 38 it is possible that the former are semiconducting (10,9) tubes and the latter are metallic (12,9) (Fig. 2b).…”

Entropy-driven stability of chiral single-walled carbon nanotubes

“…Detailed mechanisms underlying this selective growth are still debated, thus underlining the need for realistic growth models explicitly including the role of the catalyst. Existing models either focus on kinetics (10) , neglecting the role of the catalyst (11,12), but fail to calculate chiral distributions in line with experiments. Atomistic computer simulations emphasize on chemical accuracy (13,14), but need to be complemented with a model so as to provide a global understanding of the process.…”