The effect of sulfur on the number of layers in a carbon nanotube

This study shows that S concentration in the Fe catalyst plays an important role in controlling the number of graphene layers during carbon nanotube (CNT) growth via chemical vapor deposition. Using different S concentrations, we have grown thin carbon nanotubes with from 1 to 5 layers. Single-walled carbon nanotubes growing from the active surface of an FeS–Fe eutectic were observed. A growth model basing on the HRTEM characterization and thermodynamic analysis is suggested in which the CNT nucleates and grows on the active surface area of the catalyst where S accumulates in the form of an FeS–Fe eutectic, and the S distribution on the catalyst particle surface determines the number of CNT layers.