The purification of single-walled carbon nanotube (SWCNT) samples was analysed using a multi-technique approach, with structural as well as spectroscopic probes, in order to characterize the samples and to identify important factors for improvement of SWCNT sample quality. The first dry oxidation step (air at 365°C) is shown to have only a weak selectivity for the removal of the amorphous carbon or weakly organized graphitic species as well as resulting in a partial consumption of the SWCNTs. The functionalization of the SWCNTs is highly specific with formation of carboxyl, hydroxyl and carbonyl groups. On the other hand this oxidation step is highly efficient for the oxidation of the catalytic impurities (Ni, Y) which can be easily removed by subsequent acid treatment. A final high temperature treatment indicates some incomplete restoration of the quality of the SWCNT surface.

Optical emission spectroscopy (OES) is used as the main experimental tool for comparison with simulations of the plasma and gas phase composition during plasma-enhanced hot filament catalytic chemical vapor deposition (PE HF CCVD) growth of carbon nanotubes (CNTs). Calculated concentration of more than 45 species in model of the CVD reactor is acquired by Chemkin™ software. Study of different conditions is performed and a close relationship can be found between the nature and the growth rate of carbon nanostructures and the concentration of the active gas phase species. Moreover it is shown that significant changes in the density and morphology of the CNTs grown in the presence of NH3 could be mainly explained by the gas phase formation of CN and HCN.

Simulations 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.

In this paper, the growth of thin and dense films of vertically aligned carbon nanotubes (CNTs) on Fe–Co/TiN/Si(100) substrates is reported. Special attention is held to the preparation of the TiN buffer layers. This layer is deposited by pulse laser deposition at high temperature with a high texturation according to [TiN(100)//Si(100)]. Further ammonia heat treatment is performed at 623 K to control a Ti:N stoichiometry and remove oxygen impurity. Fe and Co as catalysts are subsequently deposited at high temperature (923 K) at the monolayer level with two ultrahigh vacuum evaporator cells. The growth of CNTs is performed by a direct-current plasma-enhanced and hot filaments-assisted catalytic chemical vapor deposition (dc HF CCVD) process. Highly dense films of CNTs, are obtained with only 0.5 nm Fe(Co) evaporated. Observations by transmission electron microscopy show that most of the CNTs display sizes in the 2.5–6 nm range, most of them with a double-wall (DW). This is in agreement with spectral features of the Raman radial breathing modes (RBM) in the 70–130 cm−1 range. Generally, these large-diameter DWCNTs display a high defect density with morphologies partially collapsed into flattened twisted shapes.

To support experimental investigations, a model based on Chemkin (TM) 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.

Growth of carbon nanofibers and nanotubes by combination of aerosol synthesis and plasma-enhanced catalytic chemical vapor deposition with alcohol as carbon precursor is presented. Only a hollow cathode glow discharge (HCGD) is used as gas activation process without any specific heating of the substrate. Specially designed hollow cathode enables the evaporation of catalyst directly on the substrate for catalytic growth. Product of physical vapor deposition process was examined by energy dispersive X-ray spectrometer (EDS). Spectroscopic features of the plasma were monitored by optical emission spectroscopy (OES). Carbon deposition was examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Catalytic nanofibers and multi-walled carbon nanotubes with outer diameters 20–60nm have been observed.

A mixture of acetylene, hydrogen and ammonia C2H2/H2/NH3 is used to produce carbon nanotubes (CNTs) by a plasma-enhanced catalytic chemical vapor deposition process with hot-filaments assistance (PE HF CCVD). The investigation of gas phase and surface chemistry is performed by CHEMKIN™ software. The concentration of gas phase species on the substrate is presented. Based on this study the role of various hydrocarbon and hydrogen species in the growth of carbon nanotubes is described. The role of hot-filaments in CNTs formation is presented. The synthesized nanotubes were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

A mixture of acetylene, hydrogen and ammonia (C2H2/H2/NH3) 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 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.

Functionalization of multi-walled carbon nanotubes (MWNTs) surface by sulfonated poly (ether ether ketone) SPEEK chains using a direct attachment reaction was investigated. A two step method was performed. MWNTs were oxidized by a nitric acid treatment to generate carboxyl groups on their surface. The grafting reaction of sulfonated groups of SPEEK with carboxyl groups present on the surface of oxidized MWNTs readily proceeds by using hexane diamine as an interlinking molecule. Transmission electron microscopy (TEM) shows that tubes are wrapped by polymer chains. Near edge X-ray absorption fine structure spectroscopy (NEXAFS) at the C K-edge, 0 K-edge, and N K-edge and X-ray photoelectron spectroscopy (XPS) were used to give evidence of covalent functionalization of MWNTs by SPEEK macromolecules.