The Role of a Mo Capping Layer on Fe/Al/Si in Controlling the Density and the Diameter of Carbon Nanotubes

Density- and diameter-controlled carbon nanotubes (CNTs) were synthesized on a Mo-capped Fe/Al/Si substrate by using a conventional thermal chemical vapor deposition. Scanning electron microscopy, transmission electron microscopy and Raman spectroscopy measurements consistently revealed that the density and the diameter of the CNTs could be simultaneously controlled by adjusting the thickness of the Mo capping layer (MCL) on the catalytic film. The density and the diameter of the CNTs were inversely proportional to the thickness of the MCL. X-ray photoelectron spectroscopy was used to explore the role of the MCL on a Fe/Al/Si substrate with regard to the synthesis of density- and diameter-controlled CNTs.