Increased CNT growth density with an additional thin Ni layer on the Fe/Al catalyst film

•Growth density of VA-MWNT forests could be controlled by a novel Ni/Fe/Al film.•The Fe particle density increased with diffusion of Ni in catalyst anneal process.•The Ni on Fe/Al catalyst films prevented agglomeration of fine Fe particles.•The fine Fe particles resulted in the growth of high-density MWNT forests.

Density of 3 × 1011/cm2 and diameter of CNTs of 9–12 nm were successfully controlled by using the multi-layered catalyst film consisting of an additional Ni layer on Fe/Al catalyst film. EDS analysis for the annealed catalyst films revealed that the increase of the density of Fe catalyst particles corresponded with the decrease of Ni in the films, which strongly suggested that the additional thin Ni layer on the Fe/Al multi-layered catalyst films prevented the fine Fe catalyst particles from agglomeration, resulting in the growth of high-density, and uniform diameter of CNTs.