Effect of Structures and Morphologies of Catalyst on Growth of Carbon Nanotubes Synthesized by Chemical Vapor Deposition

This study carried out the synthesis of carbon nanotubes (CNTs) on glass and Si substrates at lower than 550°C by thermal CVD using CO and H2 gases at an atmospheric pressure. Prior to CNT synthesis, catalyst layers of an Invar (an Fe‐Ni‐Co alloy) alloy were vacuum‐annealed at different temperatures to change the crystal structures and morphologies in order to elucidate their effect on the growth of CNTs. Vacuum annealing changed the crystal structures of catalyst from the hexagonal phase to the cubic phase and resulted in larger grain sizes at higher temperatures. The CNT growth on vacuum‐annealed catalyst layers showed the distinct morphological change of CNTs at the annealing temperature of 500°C. Such evolvement of CNT morphologies was explained by grain size change rather than the crystal structure change with annealing temperatures.