Comparison of single-walled carbon nanotube growth from Fe and Ni nanoparticles using quantum chemical molecular dynamics methods

Metal-catalyzed SWCNT growth has been modeled using quantum chemical molecular dynamics (QM/MD) in conjunction with feeding of carbon atoms to C ₄₀-Fe₅₅ and C₄₀-Ni₅₅ model complexes at 1500 K. The rate of Fe₅₅-catalyzed SWCNT growth determined in this work was 19% slower than the Fe₃₈-catalyzed growth rate. Conversely, Ni₅₅-catalyzed SWCNT growth exhibited a growth rate 69% larger than of Fe₅₅-catalyzed SWCNT growth, a fact consistent with excellent performance of Ni in laser evaporation and carbon-arc experiments. Ni₅₅-catalyzed growth was preceded by the formation of extended polyyne chains at the base of the SWCNT, and so differed fundamentally from Fe₅₅-catalyzed growth. These polyyne chains usually persisted for 10-30 ps. Subsequent polyyne ring condensation resulted in carbon polygon addition at the SWCNT base. The relative stabilities of the Cn carbon cluster moieties on the Fe₅₅ and Ni₅₅ surfaces were consistent with the relative strengths of the Fe-C, Ni-C and C-C interactions. The presence of smaller carbon moieties on the Fe₅₅ surface led to the dissemination of surface iron atoms, and subsequent iffusion of short C _n units through the subsurface region of the catalyst particle. Conversely, the Ni55 catalyst particle was observed to be more stable, remaining intact to a greater extent.