Dynamic observations of the effect of pressure and temperature conditions on the selective synthesis of carbon nanotubes

In situ transmission electron microscopy studies have been carried out to determine the effect of temperature and pressure on the growth of carbon nanotubes by the Ni-catalyzed chemical vapour deposition of acetylene. The temperature range explored was 450-650 degrees C and the acetylene pressure range was 0.8-20 mTorr. Our observations show that straight, single-wall, carbon nanotubes tend to form at higher temperatures and lower pressures while bent, zigzag, multi-wall carbon nanotubes form at lower temperatures and higher pressures. These results can be understood as the result of competition between the arrival rate of carbon and the nucleation rate of carbon hexagons (which increases at high pressure and low temperature), and the annealing rate of the 5-ring and 7-ring defects that are responsible for the nanotube curvature.