  Kite growth is a process that utilizes laminar gas flow in chemical vapor
deposition to grow long, well-aligned carbon nanotubes (CNTs) for electronic
application. This process uses metal nanoparticles (NPs) as catalytic seeds for
CNT growth. However, these NPs remain as impurities in the grown CNT. In this
study, nanodiamonds (NDs) with negligible catalytic activity were utilized as
nonmetallic seeds instead of metal catalysts because they are stable at high
temperatures and facilitate the growth of low-defect CNTs without residual
metal impurities. Results demonstrate the successful growth of over
100-$\mu$m-long CNTs by carefully controlling the growth conditions.
Importantly, we developed an analysis method that utilizes secondary electron
(SE) yield to distinguish whether or not CNTs grown from metal impurities. The
absence of metallic NPs at the CNT tips was revealed by the SE yield mapping,
whereas the presence of some kind of NPs at the same locations was confirmed by
atomic force microscopy (AFM). These results suggest that most of the aligned
CNTs were grown from nonmetallic seeds, most likely ND-derived NPs, via the
tip-growth mode. Structural characterizations revealed the high crystallinity
of CNTs, with relatively small diameters. This study presents the first
successful use of nonmetallic seeds for kite growth and provides a convincing
alternative for starting materials to prepare long, aligned CNTs without metal
impurities. The findings of this study pave the way for more convenient
fabrication of aligned CNT-based devices, potentially simplifying the
production process by avoiding the need for the removal of metal impurities.
