Nucleation and Growth of Single-Walled Nanotubes: The Role of Metallic Catalysts

Abstract

We present a review of experimental and theoretical results on the nucleation and growth of single-walled nanotubes, with particular emphasis on the growth of nanotube bundles emerging from catalyst particles obtained from evaporation-based elaboration techniques. General results are first discussed. Experiments strongly suggest a root-growth process in which carbon, dissolved at high temperatures in catalytic particles, segregates at the surface at lower temperatures to form tube embryos and finally nanotubes through a nucleation and growth process. A theoretical analysis of the reasons carbon does not always form graphene sheets to wrap the particles suggests analogies with other surface or interface instabilities, in particular, with those found in epitaxial growth. In the second part, detailed experimental results for nickel-rare earth metal catalysts are presented. By using various electron microscopy techniques, it is shown that carbon and the rare earth metal co-segregate at the surface of the particle and form carbide platelets, providing nucleation sites for nanotubes growing in directions perpendicular to the surface. A simple theoretical model is then presented in which the role of the rare earth metal is just to transfer electrons from metal to carbon. The graphene sheet is shown to become unstable; pentagons and heptagons are favored, which can explain the occurrence of local curvatures and of tube embryos. Finally, a brief discussion of some recent atomistic models is given.

Recent Progress on the Growth Mechanism of Carbon Nanotubes: A Review

“…The catalyzed synthesis of nanocarbon is the most popular synthesis technique, as it enhances the overall conversion of the carbon precursor and offers the possibility to improve the selectivity of the reaction by tuning the catalyst as well as the reaction conditions. [47][48][49][50][51] In addition, it benefits from existing knowledge, gained from surface science, on the interaction of hydrocarbons with transition metal surfaces, and from the pioneering work of Baker, Oberlin, and Endo on the growth of carbon fibers. [52][53][54][55][56][57][58][59][60] CNTs have been known for several decades, [56] and singlewalled carbon nanotubes (SWCNTs) since 1993.…”

“…[47][48][49][50][51][61][62][63][64][65][66][67][68][69][70][71][72] The Reviews of Moisala et al [50] and MacKenzie et al [51] provide a relatively complete list of works carried out on CCVD.…”

Simulations on the mechanism of CNT bundle growth upon smooth and nanostructured Ni as well as θ-Al2O3 catalysts

“…The formation of SW CNTs mainly requires the presence of transition-metal element or alloy catalysts (Co, Ni, Fe, Y, etc. [6][7][8]). Both separated nanotubes and their bundles were synthesized via the interaction of metal catalyst nanoparticles with carbon or hydrocarbon vapor at relatively high temperature.…”

“…In other cases, particularly in high-temperature synthesis, the nanotubes grow perpendicularly to the surface [8]. Several arguments based on classical nucleation and growth thermodynamic models have been put forward to understand how this can happen [21,22].…”

All-Electron DFT Modeling of SWCNT Growth Initiation by Iron Catalyst

“…However, Jost et al [9] discovered that in the CCVD approach both cap and circumference growth occur. An empirical model of nucleation [10] in a CCVD process assumes that carbon supersaturates melted catalyst particles and a curved graphene sheet begins to form, which evolves into a SWCNT cap and subsequently lifts off the catalyst surface. The results of molecular dynamics simulations [2,11,12] of carbon nanotube growth from carbon dissolved in a catalyst particle are in agreement with this model.…”