Influence of gas condition and growth time on the growth of a spin-capable multi-walled carbon nanotube

Spin-capable multi-walled carbon nanotube (MWCNT) forests that form webs, sheets, and yarns can play an important role in means for advancing various technologies. It is critical to understand the parameters that affect to grow spin-capable carbon nanotubes (CNTs) in a repeatable fashion. In this paper, we investigated the effects of carrier gases on the catalytic properties of iron (Fe) in the synthesis of CNT forest. We found that helium as carrier gas could effectively activate the Fe catalyst during the chemical vapor deposition (CVD) process, and increase the nucleation density of MWCNTs. Moreover, adding of hydrogen (H₂) gas is crucial for the synthesis of high-density MWCNTs. H₂ gas can suppress the agglomeration of Fe nanoparticles by Ostwald effect, which is useful for synthesizing high density. At the same time, it is also found that height of the CNT forest really depends on the growth time. A growth time of 5 min can achieve suitable sized nanoparticles with sufficient density to produce CNT forests with a higher areal density and a shorter tube spacing.