Comparison study of catalyst nanoparticle formation and carbon nanotube growth: Support effect

A comparison study has been conducted on the formation of catalyst nanoparticles on a high surface tension metal and low surface tension oxide for carbon nanotube (CNT) growth via catalytic chemical vapor deposition (CCVD). Silicon dioxide (Si O2) and tantalum have been deposited as supporting layers before deposition of a thin layer of iron catalyst. Iron nanoparticles were formed after thermal annealing. It was found that densities, size distributions, and morphologies of iron nanoparticles were distinctly different on the two supporting layers. In particular, iron nanoparticles revealed a Volmer-Weber growth mode on Si O2 and a Stranski-Krastanov mode on tantalum. CCVD growth of CNTs was conducted on irontantalum and iron Si O2. CNT growth on Si O2 exhibited a tip growth mode with a slow growth rate of less than 100 nmmin. In contrast, the growth on tantalum followed a base growth mode with a fast growth rate exceeding 1 μmmin. For comparison, plasma enhanced CVD was also employed for CNT growth on Si O2 and showed a base growth mode with a growth rate greater than 2 μmmin. The enhanced CNT growth rate on tantalum was attributed to the morphologies of iron nanoparticles in combination with the presence of an iron wetting layer. The CNT growth mode was affected by the adhesion between the catalyst and support as well as CVD process.