An investigation of the plasma composition in plasma-enhanced hot filament catalytic chemical vapor deposition of carbon nanotubes

International audienceA mixture of acetylene, hydrogen and ammonia (C2H2/H2/NH3) is used to produce carbon nanotubes (CNTs) by a plasma-enhanced catalytic chemical vapor depo- sition process either without (PE CCVD) or with hot filaments-assistance (PE HF CCVD). A mathematical model based on Chemkin computer package is used for analyzing specific conditions of nanotube synthesis. Simulations are compared with optical emission spectroscopy (OES) measurements. Morphological and structural investigations on the grown carbon nanostructures are also performed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was shown that the significant change in the density and the morphology of the CNTs grown in the presence of NH3 could be mainly explained by the gas phase formation of CN and HCN. Both species display a high etching activity, whereas the species C, CH, CH2, CH2(S), C2 and C2H are expected to be the most probable carbon nanotube precursors

Gas phase and surface kinetics in plasma and hot filament-enhanced catalytic chemical vapor deposition of carbon nanostructures

International audienceSimulations of the gas phase chemistry (C2H2/H2) coupled with surface reactions for the catalytic growth of carbon nanostructures (nanotubes/nanofibers), using different activation modes of catalytic chemical vapor deposition (CCVD) process, are presented. Deposits issued from thermal CCVD, hot-filament CCVD, plasma- enhanced CCVD and plasma-enhanced combined with hot-filament CCVD are compared to simulations of the gas phase and surface kinetics. The influence of the activation elements is described in detail. According to these simulations taking into account optical emission spectroscopy data, gas phase composition and linear growth rate of tubular nanostructures are predicted in good agreement with the experimental observations

Synthesis of carbon nanbotubes by Plasma-enhanced CVD process: gas phase study of synthesis conditions

To support experimental investigations, a model based on ChemkinTM software was used to simulate gas phase and surface chemistry during plasma-enhanced catalytic CVD of carbon nanotubes. According to these calculations, gas phase composition, etching process and growth rates are calculated. The role of several carbon species, hydrocarbon molecules and ions in the growth mechanism of carbon nanotubes is presented in this study. Study of different conditions of gas phase activation sources and pressure is performed