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

Abstract

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 ∼0.3–0.5nm, 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 5nm were identified using transmission electron microscopy and Raman spectroscopy. A relatively higher deposition temperature (∼850°C) in conjunction with a controlled catalyst and rapid growth (&amp;lt;40s) allowed for the growth of well-graphitized, high areal density (∼1012-1013∕cm2) 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.