Dynamic evolution of supported metal nanocatalyst/carbon structure during single-walled carbon nanotube growth.

Single-walled carbon nanotubes (SCWNTs) have outstanding properties that depend on structural features such as their chirality. Thus, developing a strategy to control chirality during SWCNT synthesis is critical for the exploitation of nanotube-based technologies in fields such as electronics and biomedicine. In response to this need, tuning the nanocatalyst structure has been envisioned as a means to control the nanotube structure. We use reactive classical molecular dynamics to simulate nanotube growth on supported Ni(32), Ni(80), and Ni(160) nanoparticles at various metal/support interaction strengths (E(adh)). The initial carbon ring formation is shown to correlate to the nanoparticle surface structure, demonstrating the existence of a "template effect" through a dominant occupation of hollow sites. The E(adh) strength alters the dynamic/structural behavior of the nanoparticle, in turn influencing the interplay between nanotube and nanoparticle structures. For example, the contact region between the nanoparticle surface and the growing nanotube decreases as E(adh) increases because capillary forces that raise the metal into the nanotube are counteracted by the strong metal/support interaction. The nanoparticle mobility decreases as E(adh) increases, eliminating a possible inverse template effect but hindering defect annealing in detriment of the nanotube/nanoparticle structural correlation. On the other hand, the contact between the nanoparticle and the nanotube increases with nanoparticle size. However, the heterogeneity of the nanoparticle structure increases with size, reducing the structural correlation. These results suggest that an appropriate combination of nanoparticle size and strength of the catalyst/support interaction may enhance the desired template effect and bias formation of specific nanotube chiralities.