Aligned multi-walled carbon nanotubes on different substrates by floating catalyst chemical vapor deposition: Critical effects of buffer layer

Aligned multi-walled carbon nanotubes (MWCNTs) were synthesized by floating catalyst chemical vapor deposition on two types of substrates, with emphasis on the effects of an aluminum buffer layer. It has been revealed that the presence of the aluminum buffer layer on insulating/semiconducting silicon oxide/silicon wafer resulted in a higher growth rate, narrower diameter distribution, neater morphology and improved crystalline quality of MWCNTs. When an aluminum buffer layer is deposited on electrically conductive carbon paper, high yield CNTs can be achieved while no CNTs can be observed without this buffer layer. Morphology, structure and chemical states of the products were examined by field-emission scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The generation of alumina from the aluminum buffer layer is thought to play an important role in promoting the nanotube growth. Detailed growth mechanism of MWCNTs was also discussed.