Synthesis of carbon nanotube films by thermal CVD in the presence of supported catalyst particles. Part II: The nanotube film

Carbon nanotube films have been grown at 750°and 900 °C by thermal chemical vapor deposition (CVD) with acetylene (C₂H₂) and hydrogen on silicon (0 0 2) wafers supporting preformed (Fe,Si)₃O₄ particles. The reduction of the (Fe,Si)₃O₄ particles during CVD at 750 °C was accompanied by a disintegration leading to the formation of a high density of smaller (predominantly 5-15 nm) iron silicide (α₁-Fe₂Si) particles that catalyzed the growth of a dense and aligned multi-wall carbon nanotube film. The tubes did not contain any inclusions apart from the catalytic particles present in the bottom part of the film, and it was concluded that the nanotubes grew via a "base-growth" mechanism. CVD at 900 °C resulted in a random growth of predominantly multi-wall carbon nanotubes. The film contained an increased number of amorphous carbon, or graphite, clusters containing particles that had been carbonized, the larger ones to cementite, θ-Fe₃C. Nanotubes were observed to grow from some of these clusters. Multi-wall carbon nanotube tips contained after CVD at 900 °C encapsulated θ-Fe₃C, or in a few cases α- or γ-Fe, particles.