Role of thin Fe catalyst in the synthesis of double- and single-wall carbon nanotubes via microwave chemical vapor deposition

Synthesis of vertically aligned small diameter (single- and double-wall) carbon nanotube films on thermally oxidized n(+)-Si(001) wafers, with acetylene diluted with ammonia gas mixture using a microwave plasma-assisted chemical vapor deposition technique, is reported. Experiments show that by continuous reduction in the thickness of the iron catalyst film to similar to0.3-0.5 nm, or alternately, smaller catalyst particles produces hollow concentric tubes with a fewer number of walls. Double- and single-wall carbon nanotubes with diameters ranging from 1 to 5 nm were identified using transmission electron microscopy and Raman spectroscopy. A relatively higher deposition temperature (similar to850degreesC) in conjunction with a controlled catalyst and rapid growth (<40 s) allowed for the growth of well-graphitized, high areal density (similar to10(12)-10(13)/cm(2)) nanotubes with reduced amorphous carbon and iron. Our results also indicate that the base growth is the most appropriate model to describe the growth mechanism for the nanotube films. (C) American Institute of Physics.