Predicting the Chiral Enrichment of Metallic SWCNTs on Ni–Cu Bimetallic Surfaces

Abstract

Previous modeling and experimental studies have suggested that Cu-based metal catalysts can preferentially produce metallic carbon nanotubes. Here, we explain this selectivity by separately modeling nanotube cap nucleation and nanotube growth on Cu and Ni x Cu 1−x surfaces. Cap nucleation is modeled by invoking an epitaxial lattice matching criterion and comparing the binding strengths of different cap chiralities. Nanotube growth on various catalyst surfaces was studied by calculating differences in armchair and zigzag dangling bond energies, relative chemical activity ratios, and nanotube growth rates of different nanotube chiralities. All energies associated with nanotube cap nucleation and armchair and zigzag dangling bond energies were obtained using density functional theory (DFT). We find that certain armchair and zigzag nanotube caps exhibit higher binding strengths than chiral caps, and the stability of the caps on the various surfaces decreases as Ni > Ni 0.5 Cu 0.5 > Cu, in accordance with the respective carbon−metal adhesion strengths. Both the relative chemical activity ratios and the nanotube growth rates suggest that Ni x Cu 1−x bimetallic nanoparticles with increased bond length or lattice-strained surfaces are excellent candidates for preferentially producing metallic nanotubes.

Kinetics-Controlled Growth of Metallic Single-Wall Carbon Nanotubes from CoRex Nanoparticles

“…We can see that a high Re content, low growth temperature, low carbon source feed rate, and short growth time increase the selective growth of m-SWCNTs. Our result is consistent with Bhethanabotla et al ’s theoretical study, which shows that bimetallic Ni 0.5 Cu 0.5 nanoparticles with a large lattice strain or longer average bond length would lead to a significant increase in the growth rate of metallic SWCNTs …”

“…Our result is consistent with Bhethanabotla et al's theoretical study, which shows that bimetallic Ni 0.5 Cu 0.5 nanoparticles with a large lattice strain or longer average bond length would lead to a significant increase in the growth rate of metallic SWCNTs. 31 CONCLUSION Kinetics-induced selective growth of m-SWCNTs was realized by manipulating the binding energy between the SWCNTs and the CoRe x alloy catalyst and promoting the growth rate difference under quasi-static CVD conditions. Dispersed CoRe 4 nanoparticles with a mean diameter of 2.3 nm prepared by a BCP assembly method were used to grow SWCNTs by CVD.…”

“…Recently, the growth kinetics have been proposed to determine the abundance of SWCNTs grown with a particular chirality. ,− On the one hand, Wei et al reported that ultralong s-SWCNTs were preferentially obtained with a high growth rate of ∼80 μm/s, while the growth of m-SWCNTs was terminated earlier . On the other hand, (12, 6) m-SWCNTs were enriched at a relatively lower growth rate of less than 5 μm/min. ,,,, These results indicate that the type of SWCNTs is closely related to their growth rate, which is mainly determined by catalyst–SWCNT interaction and chemical vapor deposition (CVD) growth conditions, such as temperature and carbon feeding rate. , A catalyst particle may have different interfacial binding energies with SWCNTs with different charilities, − which leads to different SWCNT growth rates.…”