Linking growth mode to lengths of single-walled carbon nanotubes

Abstract

International audienceElucidating the key factors that determine the lengths of single-walled carbon nanotubes (SWCNTs) is of great importance for understanding the origin of chiral selectivity. We use transmission electron microscopy to thoroughly investigate as-grown SWCNTs. The lengths and growth modes of SWCNTs were decided by bright-field imaging. Their respective chiral angles were calculated on the basis of nanobeam diffraction patterns. Systematic investigations reveal that there is no correlation between the SWCNT length and its chiral angle. Instead, it shows that SWCNT lengths depend more on their growth mode, i.e. the link between SWCNT and its seeding catalyst particle. Atomistic computer simulations demonstrate that low carbon fractions in the catalyst lead to so-called tangential growth, with a partial wetting of the metal in the tube, where metal catalyst tends to be deactivated by graphite layer encapsulation and results in short SWCNTs. In contrast, a high carbon concentration inside metal particle favors perpendicular growth modes, where only the tube lip is in contact with the catalyst. Catalysts adopting perpendicular mode could have a longer lifetime, thus catalyze the growth of long SWCNTs. Finally, the carbon concentration related growth mode was applied to interpret diverse SWCNT growth results

A Facile Synthesis of FeCo Nanoparticles Encapsulated in Hierarchical N‐Doped Carbon Nanotube/Nanofiber Hybrids for Overall Water Splitting

“…CNTs were still not observed when doubling the concentration of Fe and Co (FeCo@NC‐22) which might be due to higher NP density (∼twice compared to other samples) and relatively earlier encapsulation of NP. When the carbon fraction is low the strong adhesion energy will not allow the dewetting of NPs and subsequent tip‐growth of CNTs . Thus, it can be concluded with support from the investigations by Aguiar‐Hualde et al .…”

“…When the carbon fraction is low the strong adhesion energy will not allow the dewetting of NPs and subsequent tip-growth of CNTs. [27][28] Thus, it can be concluded with support from the investigations by Aguiar-Hualde et al [27] that FeCo in 1 : 1 and 1 : 2 are more favorable for the initial growth of CNTs. Moreover, the NF diameter decreased to 243 � 51 nm and 250 � 31 nm for FeCo@NC-11 and FeCo@NC-12, respectively, in comparison to 286 � 98 nm for the pristine NCNF, possibly due to the effect of conducting metal salts in the solution which electrostatically aids in nanofibers thinning during electrospinning.…”

Growth modes and chiral selectivity of single-walled carbon nanotubes

“…Tubes were grown at 1073 K using two different CVD reactors. The first one is a horizontal furnace, described in [25], that enables surface bound growth of SWNTs using Fe as a catalyst, and CO or CH 4 as carbon feedstocks. Catalyst preparation and experimental setups and protocols are described in section Methods.…”

Probing the role of carbon solubility in transition metal catalyzing single-walled carbon nanotubes growth

“…This is sometimes illustrated in the form of a so-called "volcano plot" showing that popular catalysts (Fe, Co, Ni) display a large enough affinity for carbon, to adsorb carbon precursor molecules in the surface layers and possibly dissolve some carbon inside the NP. Indeed, this carbon content favors the dewetting of the nanoparticle with respect to the sp 2 carbon wall, a necessary property to limit catalyst encapsulation and deactivation [9][10][11] . Despite such progresses, a notable lack of understanding of the roles played by carbon solubility in the catalyst during the SWNT growth process plagues our ability to optimize synthesis conditions and ultimately control the structure of the tubes.…”