Atomic hydrogen-driven size control of catalytic nanoparticles for single-walled carbon nanotube growth

The effects of an atomic hydrogen (H_at) pretreatment of the catalyst layer on the low temperature growth of single-walled carbon nanotubes (SWCNTs) have been investigated using a modified catalytic chemical vapor deposition system. Well-defined and isolated individual Fe nanoparticles as a catalyst are successfully formed on the defects with high trapping energy which are created on the Al₂ O₃ surface by H_at pretreatment, yielding highly dense SWCNTs. The pretreatment mechanism of HH_at, compared to H₂, is also discussed. It was also found that the quality of SWCNTs can be enhanced when H_at is flowed with CH₄ during nanotubes growth at low temperature. In this case, the undesired carbon products and defects on catalyst seeds and nanotube walls can be selectively removed by H_at. Therefore it is essential to use H at in the pretreatment stage for increasing catalytic activity and to keep the size of nanoparticles in the nm range. H_at can also be employed in growth stage for enhancing SWCNTs quality and density at low temperature.