Ferric-sulfate-catalysed hot filament chemical vapour deposition carbon nanotube synthesis

This paper reports on the first use of a sulfur-containing substrate catalyst (ferric sulfate) in a hot filament chemical vapour deposition (HFCVD) reactor for carbon nanotube synthesis. The study combines three attractive features concerning catalysis, nucleation, and morphological control of nanotube growth in this context. First, it involves enhancement of iron's catalysis action by sulfur, proven effective previously in a similar capacity in chemical vapour deposition (CVD) studies not involving a hot filament. Second, it involves reduction of an iron compound with atomic hydrogen in the HFCVD reactor, which, through production of a fine dispersion of reduced substrate iron particles is a facilitating step in carbon nanotube nucleation. Third, for control of carbon nanotube morphology, it uses the CVD variables method, which uses the inherent capabilities of changes in CVD variables to control the growth morphology of carbon nanotubes. It is demonstrated in this report that the combination of these attractive features has enabled us to produce both randomly oriented and vertically aligned carbon nanotubes.