Growth valley dividing single- and multi-walled carbon nanotubes: combinatorial study of nominal thickness of co catalyst

The relationships among the nominal thickness of Co catalysts, the structure of the catalyst particles, and the structure of carbon nanotubes (CNTs) growing from the catalysts were investigated. A gradient thickness profile of Co was prepared using a combinatorial method and then subjected to alcohol catalytic chemical vapor deposition at 700 °C. In the deposited sample, two active regions appeared on either side of an inactive region. In the active regions, mainly single-walled carbon nanotubes (SWNTs) or multi-walled carbon nanotubes (MWNTs) grew, depending on the nominal Co thickness (SWNTs grown at a Co thickness of about 0.1 nm, and MWNTs grown at a Co thickness of about 1.5 nm). However, neither SWNTs nor MWNTs grew efficiently at a moderate Co thickness (∼0.4 nm). This dependence of CNT growth on the initial Co thickness is explained by the different mechanisms of catalyst particle formation from sub-nanometer-thick and nanometer-thick Co films.