Effect of the State of Catalytic Nanoparticles on the Growth of Vertically Aligned Carbon Nanotubes

Abstract

In this study, vertically aligned carbon nanotubes (VA-CNTs) were grown from filler-added LB films with accumulated AlFe₂O₄ nanoparticles and palmitic acid (C16) as the filler molecule after different hydrogen reduction temperatures of 500^°C and 750^°C, and the grown VA-CNTs were compared and evaluated. As a result, VA-CNTs were approximately doubled in length after 500^°C hydrogen reduction compared to 750^°C hydrogen reduction when AlFe₂O₄ NPs were used. On the other hand, when the catalyst area ratio was decreased by using palmitic acid, i.e., the distance between CNTs was increased, VA-CNTs rapidly shortened after 500^°C hydrogen reduction, and VA-CNTs were no longer obtained even in the range where VA-CNTs were obtained in 750^°C hydrogen reduction. The inner and outer diameters of VA-CNTs decreased with decreasing catalyst area ratio at 750^°C hydrogen reduction and tended to increase at 500^°C hydrogen reduction. The morphology of the catalyst nanoparticles after CVD was observed to change significantly depending on the hydrogen reduction temperature and catalyst area ratio. These observations indicate that the state of the catalyst nanoparticles immediately before the CNT growth process greatly affects the physical properties of the CNTs.