An Investigation of the Plasma Composition in Plasma-enhanced Hot Filament Catalytic Chemical Vapor Deposition of Carbon Nanotubes

Abstract

A mixture of acetylene, hydrogen and ammonia (C 2 H 2 /H 2 /NH 3 ) is used to produce carbon nanotubes (CNTs) by a plasma-enhanced catalytic chemical vapor deposition 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 NH 3 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, CH 2 , CH 2 (S), C 2 and C 2 H are expected to be the most probable carbon nanotube precursors.

Plasma‐Assisted Approaches in Inorganic Nanostructure Fabrication

“…CH x radicals and H atoms are often observed [59,67] and their presence is further confirmed by numerical simulation. [68,69] In the NH 3 /C 2 H 2 growth system, some nitrogencontaining species such as CN and NH radicals are also recognized. [59,66] Combining the OES and MS techniques, Woo et al extensively studied the CNT growth process in the CH 4 / NH 3 /H 2 system and tried to correlate the growth behavior to the plasma diagnostics results.…”

“…[61,[100][101][102][103] The excited neutrals including atoms, radicals, and molecules at excited electronic states consist of the majority of growth species in many materials systems. [69,85,[104][105][106] New chemistry can be introduced by these excited species, leading to chemical reactions at lower temperature or even thermodynamically forbidden conditions. [57,87,89,142] The nucleation, growth, and crystallization behavior of the nanostructures can be tuned due to the new chemistry equilibrium induced by the excited species at the plasma/solid interface.…”

High-quality single-walled carbon nanotubes synthesis by hot filament CVD on Ru nanoparticle catalyst

“…These results indicate that high quality SWCNTs can be effectively grown with hot filament assistance. The CH 4 pre-decomposition into carbon radicals and hydrocarbon species when it passed through the filament leads to an increased concentration of reactive carbon species on the catalyst particles [10,30]. This may explain the higher yield of SWCNTS on the surface, the enhanced growth rate and the lower number of defaults of the resulting nanotubes.…”

The CVD Modes of Carbon Nanotubes Growth Studied by Gas-Phase Investigations and Modelization

“…As a result of this study the simulated growth rate for all conditions and types of C CVD is calculated and compared with a rather fair agreement with the experimental measured ones, while this growth rate is varying by several orders of magnitude. The concentration of more than 40 species (including charged species) produced by decomposition of a C2H2/H2/NH3 mixture is presented and compared to the relative concentration acquired by optical emission spectroscopy of the plasma [6] . The role of the different gas phase species and their participation on the CNTs synthesis in the way of activation, nucleation, growth or poisoning of catalytic particle is discussed.…”