Tunable self-assembly of carbon nanotubes on silica surface

We report here self-assembly behaviors of carbon nanotubes on planar silica substrates, tunable with a catalytic chemical vapor deposition (CVD) approach. In this CVD process, different from several approaches reported, the catalyst (from ferrocene) and carbon (from xylene) are introduced simultaneously via the vapor phase; thus the ratio of catalyst/carbon in the vapor phase can be adjusted, which tunes the assembly behavior and growth pathways of nanotubes. Depending on this ratio, carbon nanotubes organize themselves into growth units of crystal-like, spherulite-like and honeycomb networks, at the early growth stages. Prolonged deposition leads to the nanotubes films of different morphologies, developed from these units. Our study provides the first ever glimpse of early stages of nanotubes growth and possible pathways through which nanotubes assemble and grow into continuous films.