Effects of carbon content in iron catalyst coatings on the growth of vertically aligned carbon nanotubes on smooth silicon surfaces by thermal chemical vapor deposition

Carbon content in sputter coated iron catalyst was found to be an important parameter for the successful growth of vertically aligned carbon nanotubes on smooth silicon surfaces by means of thermal chemical vapor deposition (CVD). Pre-saturation of iron catalyst nanoparticles with carbon reduced the difference in the induction time for the growth of carbon nanotubes. This allows neighboring carbon nanotubes to support each other from its initial growth phase and thus effectively prevent them from growing into randomly oriented carbon nanotube networks on smooth silicon substrates. Cast iron containing carbon was found to be an effective sputtering target for achieving the growth of vertically aligned carbon nanotubes on smooth silicon surfaces. On the contrast, pure iron sputtering target was found to be ineffective. Correlation of in-situ measured sheet resistance of sputter coated iron catalyst with the alignment of carbon nanotubes revealed the optimal control of the amount of carbon containing iron catalyst coatings for the growth of vertically aligned carbon nanotubes on smooth silicon surfaces. The optimal catalyst coating was when the in-situ measured sheet resistance vs. sputtering time was near the transitional zone between that with rapidly declining sheet resistance and that with slow declining sheet resistance with respect to sputtering time. Co-sputtering of an iron target partially covered by graphite sheets as well as sequential sputtering of pure iron and graphite were also applied to confirm the effectiveness of carbon content in iron coatings for the growth of vertically aligned carbon nanotubes.