Interplay of Catalyst Size and Metal−Carbon Interactions on the Growth of Single-Walled Carbon Nanotubes

Abstract

Single-walled carbon nanotubes grow by decomposition of a carbon-containing precursor gas over metal nanocatalysts. It is known that the shape, size, and chemical nature of the catalysts play significant roles in the nucleation and growth processes. Here, we use reactive molecular dynamics simulations to analyze how the catalyst particle size and the strength of adhesion between the surface and nascent carbon structures may affect the growth process. As a result, we determine if the process leads to cap lift-off or if it causes graphitic encapsulation and, therefore, poisoning of the catalyst. In agreement with the Hafner-Smalley model, our MD simulation results illustrate that the work of adhesion must be weak enough so the curvature energy of a spherical fullerene is less favorable than that of a single-walled carbon nanotube with the same diameter, thus allowing the cap-lifting process to take place. Moreover, we propose that a simple model combining curvature energy and kinetic effects may help to identify regions of single-walled carbon nanotube growth in the phase space defined by work of adhesion, temperature, and catalyst size.

Thermodynamic and Energetic Effects on the Diameter and Defect Density in Single-Walled Carbon Nanotube Synthesis

“…This correction depends on the number of carbon atoms around the perimeter of the cap, which is proportional to d. On a per carbon atom basis, this correction is proportional to d −1 since the number of carbon atoms in the cap is proportional to d 2 . On the basis of previous reports, 45,47,48 these corrections may be on the same order of magnitude as the strain energy.…”

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

“…This hypothesis is further supported by DFT results obtained by Bolton's group [131][132] as well as recent MD calculations of Yakobson's group. [133][134] The latter showed that the catalyst particle either grows a SWCNT or gets encapsulated, depending on an interplay of the curvature energy and the work of adhesion of carbon to the metal particle. In the early stages of the reaction, as the carbon cap forms, the curvature energy plays a decisive role.…”

Simulation and modeling of carbon nanotube synthesis: current trends and investigations

“…The system with a CNT attached to a pure Ni cluster was found to be energetically favored compared with a system containing the same CNT attached to nickel carbide. Burgos et al [43] used reactive MD simulations to analyze how the catalyst particle size and the strength of adhesion between the surface and the nascent carbon structures may affect the growth process. The MD simulations results illustrated that the work of adhesion must be weak enough so that the curvature energy of a spherical fullerene is less favorable than that of a SWCNT with the same diameter, to allow the cap-lifting process to take place.…”

“…The salient feature of this approach is that it directly gives the total energy and local adhesion energy of the system. Burgos et al [43,44] used the most suitable potentials for different types of interactions involved, in their simulations. By this, the realistic modeling of the most important interactions in the synthesis process was possible, which provided a close insight over reaction pathways and at the nucleation and the initial stages of growth.…”