Synthesis of carbon nanotube films by thermal CVD in the presence of supported catalyst particles. Part I: The silicon substrate/nanotube film interface

The interface between the silicon substrate and a carbon nanotube film grown by thermal CVD with acetylene (C2H2) and hydrogen at 750 or 900degreesC has been characterized by high resolution and analytical transmission electron microscopy, including electron spectroscopic imaging. Silicon (002) substrates coated with a thin (2.8 nm) iron film were heat treated in the CVD furnace at the deposition temperature in a mixture of flowing argon and hydrogen whereby nanosized particles of (Fe,Si)(3)O-4 formed. These particles were reduced to catalytic iron silicides with the alpha-(Fe, Si), alpha(2)-Fe2Si and alpha(1)-Fe2Si structures during CVD at 900degreesC, and multi-wall carbon nanotubes grew from supported particles via a base-growth mechanism. A limited number of intermediate iron carbides, hexagonal and orthorhombic Fe7C3, were also present on the substrate surface after CVD at 900degreesC. The reduction of the preformed (Fe, Si)(3)O-4 particles during thermal CVD at 750degreesC was accompanied by disintegration leading to the formation of a number of smaller ( < 5 and up to 10 nm) iron and silicon containing particles. It is believed that the formation of these small particles is a prerequisite for the growth of aligned multi-wall carbon nanotube films. (C) 2004 Kluwer Academic Publishers.