The role of the catalytic particle temperature gradient for SWNT growth   from small particles
  The Vapour-Liquid-Solid (VLS) model, which often includes a temperature gradient (TG) across the catalytic metal particle, is often used to describe the nucleation and growth of carbon nanostructures. Although the TG may be important for the growth of carbon species from large metal particles, molecular dynamics simulations show that it is not required for single-walled carbon nanotube growth from small catalytic particles. 
Feng Ding, Arne Rosen, Kim Bolton