Abstract
Multi-walled carbon nanotubes (MWCNTs) were grown by plasma-enhanced chemical vapor deposition (PECVD) in a bell jar reactor. A mixture of methane and hydrogen (CH4/H2) was decomposed over Ni catalyst previously deposited on Si-wafer by thermionic vacuum arc (TVA) technology. The growth parameters were optimized to obtain dense arrays of nanotubes and were found to be: hydrogen flow rate of 90 sccm; methane flow rate of 10 sccm; oxygen flow rate of 1 sccm; substrate temperature of 1123 K; total pressure of 10 mbar and microwave power of 342 Watt. Results are summarized and significant main factors and their interactions were identified. In addition a computational study of nanotubes growth rate was conducted using a gas phase reaction mechanism and surface nanotube formation model. Simulations were performed to determine the gas phase fields for temperature and species concentration as well as the surface-species coverage and carbon nanotubes growth rate. A kinetic mechanism which consists of 13 gas species, 43 gas reactions and 17 surface reactions has been used in the commercial computational fluid dynamics (CFD) software ANSYS Fluent. A comparison of simulated and experimental growth rate is presented in this paper. Simulation results agreed favorably with experimental data.
Highlights
Since their discovery by Iijima in 1991 [1], carbon nanotubes have generated much interest due to their quasi one-dimensional structure and their unique combinations of electronic, field emission, mechanical and chemical properties coupled with the new ability to grow them aligned on a substrate
For microwave plasma-enhanced chemical vapor deposition (PECVD) nanotube synthesis we developed an experimental protocol composed by three steps: 1) thermal annealing of Ni/Si substrates, 2) hydrogenation of Ni catalyst, 3) nanotube growth
Atomic force microscopy (AFM) of the as produced by thermionic vacuum arc (TVA) Ni/Si substrates and annealed at 850 ̊C during 20 minutes hydrogenated with pure hydrogen plasma during 10 minutes was carried out to determine the surface morphology
Summary
Since their discovery by Iijima in 1991 [1], carbon nanotubes have generated much interest due to their quasi one-dimensional structure and their unique combinations of electronic, field emission, mechanical and chemical properties coupled with the new ability to grow them aligned on a substrate. This opened unlimited possibilities of applications such as field emitters, sensors, high-density energy storage devices, photonic crystals, active media for lasers, non-linear optical media etc. The addition of a controlled amount of a weak oxidizer as oxygen or water into the growth ambient of CVD was reported to significantly enhance the activity and lifetime of the catalyst resulting in efficient nanotubes growth [6] [7]
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