Mechanism and Kinetics of Growth Termination in Controlled Chemical Vapor Deposition Growth of Multiwall Carbon Nanotube Arrays

• Published in: Nano letters 2009-02, Vol.9 (2), p.738-744
• Main Authors: Stadermann, Michael, Sherlock, Sarah P, In, Jung-Bin, Fornasiero, Francesco, Park, Hyung Gyu, Artyukhin, Alexander B, Wang, Yinmin, De Yoreo, James J, Grigoropoulos, Costas P, Bakajin, Olgica, Chernov, Alexander A, Noy, Aleksandr
• Format: Article
• Language: English
• Subjects: Catalytic methods; Chemical vapor deposition (including plasma-enhanced cvd, mocvd, etc.); Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Kinetics; Materials science; Methods of deposition of films and coatings; film growth and epitaxy; Methods of nanofabrication; Microarray Analysis; Microscopy, Electron, Scanning; Microscopy, Electron, Transmission; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Nanotubes; Nanotubes, Carbon - chemistry; Nanotubes, Carbon - ultrastructure; Physics; Volatilization
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/nl803277g

We have investigated growth kinetics of multiwall carbon nanotube (MWCNT) arrays produced by catalytic thermal decomposition of ethylene gas in hydrogen, water, and argon mixture. The MWCNT growth rate exhibits a nonmonotonic dependence on total pressure and reaches a maximum at ∼750 Torr of total pressure. Water concentrations in excess of 3000 ppm lead to the decrease in the observed growth rate. Optimal pressure and water concentration combination results in a reliable growth of well-aligned MWCNT arrays at a maximum growth rate of ∼30 μm/min. These MWCNT arrays can reach heights of up to 1 mm with typical standard deviations for the array height of less than 8% over a large number of process runs spread over the time of 8 months. Nanotube growth rate in this optimal growth region remains essentially constant until growth reaches an abrupt and irreversible termination. We present a quantitative model that shows how accumulation of the amorphous carbon patches at the catalyst particle surface and the carbon diffusion to the growing nanotube perimeter causes this abrupt growth cessation. The influence of the partial pressures of ethylene and hydrogen on the ethylene decomposition driving force explains the nonlinear behavior of the growth rate as a function of total process pressure.