  Single-, double- and triple-walled carbon nanotubes (SWNTs, DWNTs and TWNTs)
have been controlla- bly synthesized by an arc discharge method using asphalt
as carbon source. The morphology and struc- ture of three kinds of products
synthesized with Fe as catalyst were characterized by scanning electron
microscopy (SEM), high-resolution transmission electron microscopy (HRTEM),
Raman spectroscopy and energy dispersive X-ray spectroscopy (EDX). It was found
that different buffer gases strongly affect the number layers in the
synthesized nanotubes. In the He gas atmosphere only SWNTs were found to be
synthesized by arc discharge in contrast to the case in Ar gas atmosphere in
which only TWNTs were formed. In N2 atmosphere both SWNTs and DWNTs were
synthesized. Our findings indicate that asphalt is a suitable industrial carbon
source for the growth of different type nanotubes.
