Morphological Evolution of Fe-Mo Bimetallic Catalysts for Diameter and Density Modulation of Vertically Aligned Carbon Nanotubes

FeMo bimetallic catalyst is a promising candidate for achieving efficient growth and fine structures of vertically aligned carbon nanotubes (VA-CNTs) by catalytic chemical vapor deposition (CVD). Understanding the surface morphological evolution of a bilayer metal film and accompanied changes in the resultant CNT structure is a key to modulating the VA-CNT growth. We correlate the growth rates and individual CNT structures with the FeMo catalyst morphological evolution. At CVD conditions, the layered bimetallic films evolve into entirely different ensembles of polydispersed nanoparticles depending on the ratio and stacking order between Fe and Mo. Specifically, Fe-on-Mo type pronounced bimodality in size than do Mo-on-Fe type nanofilm nanofilms develop to denser and smaller nanoparticles with more s, leading to better alignment and unique diameter distribution of resultant CNTs. Also, the decrease in the catalytic activity of Mo-rich Fe-Mo nanoparticles can contribute to the diameter, alignment, and density modulation of VA-CNTs.