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

Abstract

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 approximately 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 approximately 30 microm/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.

Data-driven understanding of collective carbon nanotube growth by in situ characterization and nanoscale metrology

“…This collective growth picture emerged in contrast to studies that explain CNT forest growth behavior based on mathematical modeling of the behavior of a single catalyst nanoparticle-CNT system. 9,36,87,88 As shown in Fig. 9(b), the mass kinetics exhibit an S-shaped curve, which is fitted by the Gompertz model of population growth.…”

“…15,34 Moreover, the growth mechanism was shown to shift between tip growth and base growth based on the diameter of the catalyst nanoparticle. 35 Previously, backscatter-electron imaging was used to show that there are no traces of metal nanoparticles on the top of grown CNT forests, 36 to confirm the base-growth process for Fe nanoparticle catalysts on aluminum oxide support layers. The rest of this article will focus on studying this catalyst system.…”

Simulation and modeling of carbon nanotube synthesis: current trends and investigations

“…(2009) [9] Carbon nanotube synthesis by fluidized bed chemical vapor deposition [15] CNT synthesis by the CVD process…”

“…Stadermann et al [9] presented a quantitative model that showed how accumulation of amorphous carbon patches at the catalyst particle surface and carbon diffusion to the growing nanotube perimeter causes an abrupt growth cessation. In their studies, the effect of partial pressures of ethylene and hydrogen on the driving force for ethylene decomposition was used to explain the nonlinear behavior of the growth rate as shown in Figure 3B.…”

“…Diffusion limited growth is the main attractive feature of the model developed by Stadermann et al [9] for the growth of nanotube arrays under controlled conditions. Hence, the tight control over CNT array dimension was possible, which is essential in their incorporation into micro electro mechanical system (MEMS) and nano electro mechanical system (NEMS) devices.…”