Temperature and time dependence of the growth of carbon nanotubes by thermal chemical vapor deposition

Multiwalled carbon nanotubes(CNTs) were synthesized on Ni-coated Si substrates by thermal chemical vapor deposition (CVD) with an acetylene as. Ni thin film with a thickness of 120 nm was prepared at 200 degreesC under a pressure of 3 x 10(-3) Torr by RF magnetron sputtering. The CNTs grown at a growth temperature of 650 degreesC were uniformly aligned with high tube density. We obtained relatively less aligned CNTs with lower tube density with increasing growth temperatures, in contrast to the general belief. This was explained by the change of the surface morphology of the metal layers, where with increasing the growth temperatures the metal grains were coalesced and thus the grain size became bigger, reducing the grain density. The length of the CNTs increased with increasing growth time and saturated at long growth time. The growth termination at large growth time is explained by the cap growth mechanism.