Effects of pre-treatment and plasma enhancement on chemical vapor deposition of carbon nanotubes from ultra-thin catalyst films

• Published in: Diamond and related materials 2006-04, Vol.15 (4), p.1029-1035
• Main Authors: Cantoro, M., Hofmann, S., Pisana, S., Ducati, C., Parvez, A., Ferrari, A.C., Robertson, J.
• Format: Article
• Language: English
• Subjects: Chemical vapor deposition; Chemical vapor deposition (including plasma-enhanced cvd, mocvd, etc.); Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Methods of nanofabrication; Nanofibers; Nanoscale materials and structures: fabrication and characterization; Nanotubes; Physics; Plasma CVD
• ISSN: 0925-9635; 1879-0062
• DOI: 10.1016/j.diamond.2006.01.007

We report a detailed study of surface-bound chemical vapor deposition of carbon nanotubes and nanofibers from evaporated transition metal catalysts exposed to ammonia diluted acetylene. We show that a reduction of the Fe/Co catalyst film thickness below 3 nm results into a transition from large diameter (> 40 nm), bamboo-like nanofibers to small diameter (∼ 5 nm) multi-walled carbon nanotubes. The nanostructuring of ultra-thin catalyst films critically depends on the gas atmosphere, with the resulting island distribution initiating the carbon nucleation. Compared to purely thermal chemical vapor deposition, we find that, for small diameter nanotube growth, DC plasma assistance is detrimental to graphitization and sample homogeneity and cannot prevent an early catalyst poisoning.