Iridium catalyzed growth of vertically aligned CNTs by APCVD

• Growth of uniform-diameter vertically-aligned multi-walled CNTs by APCVD.
• Use of high melting point low carbon solubility iridium nanoparticles as catalyst.
• Optimization of growth time for uniform sized, uniformly aligned CNTs.
• Growth model for the various features in the vertically aligned CNTs is proposed.

Vertically aligned carbon nanotubes (VA-CNTs) have been synthesized using high temperature catalyst nanoparticles of iridium. The catalyst layer was prepared by DC sputtering. Particle density, circularity and average particle size of the catalyst were analyzed using field emission scanning electron microscopy. The alignment, morphology and the length of the as-grown CNTs were analyzed using field-emission scanning electron microscopy. High resolution transmission electron microscopy was carried out to observe the layers of graphitic stacking which form the carbon nanotubes. Micro Raman measurement was used for the analysis of the graphitic crystallinity of the as-grown carbon nano structures. Effects of growth time variation on growth morphology and alignment have been studied. The alignment has been explained on the basis of the crowding effect of the neighboring nanoparticles.