Carbon-based nanostructures continue to attract a disproportionate share of research effort because of their wide range of properties. This research includes synthesis techniques and controlling the structure and morphology of nanomaterials, since for many applications tedious manipulations are often required. One of the problems faced in such a characterization is contamination. Carbon nanotubes (CNTs) have been synthesized by hot filament plasma enhanced catalytic chemical vapour deposition (HF PE CCVD) and investigated by x-ray absorption near-edge spectroscopy (XANES). The spectra showed that samples with a large surface curvature are less sensitive to thermal treatment. Among the contaminants, we find potassium, which may have come from the beam line.

We report a quantitative x-ray absorption spectroscopy (XAS) study of the orientation of carbon nanotubes (CNTs) grown on plain SiO2(thickness 8 nm)/Si(100) substrates by a catalytically enhanced dc hot filament chemical vapour deposition (CVD) process. The alignment and orientation of CNT films are generally provided in the literature by scanning electron microscope (SEM) and transmission electron microscope (TEM) images qualitatively. A very few other techniques have been used to more deeply study the alignment of CNTs grown by the CVD technique, such as x-ray diffraction (XRD) or grazing-incidence small-angle x-ray scattering (GISAXS). XAS recorded on the C K-edge provides information on the local environment around carbon atoms and helps us study the orientation of CNTs. We find spectral features very similar to those of HOPG, in agreement with the literature. Meanwhile, we do not observe any extinction of the π* band at grazing incidence. CNTs have an averaged direction perpendicular to the surface of the substrate.

X-Ray Absorption Spectroscopy (XAS) on the carbon K edge of carbon nanostructures (nanotubes, nanofibers, nanowalls) is reported here. They are grown on plain SiO2 (8 nm thick)/Si(100) substrates by a Plasma and Hot Filaments-enhanced Catalytic Chemical Vapor Deposition (PE HF CCVD) process. The morphology and the nature of these carbon nanostructures are characterized by SEM, TEM and Raman spectroscopy. According to conditions of catalyst preparation and DC HF CCVD process, carbon nanotubes (CNTs), carbon nanofibers (CNFs), carbon nanowalls (CNWs), carbon nanoparticles (CNPs) with different orientation of the graphene plans or shells can be prepared. From the angular dependence of the incident light and geometrical morphology of the nanostructures, wide variations of the C K-edge intensity of the transitions to the empty * π and * σ states occur. A full lineshape analysis of the XAS spectra has been carried out using a home-made software, allowing estimating the relative proportion of * π and * σ transitions. A geometrical model of the angular dependence with the incidence angle of the light and the morphology of the carbon nanostructures is derived. With normalization to the HOPG (Highly Oriented Pyrolytic Graphite graphite) reference case, a degree of alignment can be extracted which is representative of the localized orientation of the graphitic carbon π bonds, accounting not only for the overall orientation, but also for local defects like impurities incorporation, structural defects ... This degree of alignment shows good agreement with SEM observations. Thus CNTs films display degrees J. M. Mane et al. 967 of alignment around 50%, depending on the occurrence of defects in the course of the growth, whereas no special alignment can be detected with CNFs and CNPs, and a weak one (about 20%) is detected on CNWs.

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, O 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.

We report a quantitative Grazing Incidence Small Angle X-Ray Scattering (GISAXS) study of the alignment of mutually oriented carbon nanotubes (CNTs) grown by a catalytically-activated, a plasma direct current and hot filaments-assisted (DC HF CCVD) process. Metallic catalytic (Co) islands were dispersed on plain SiO 2 (5 nm thickness)/Si(100) substrates prior the growth of CNTs which can be considered as highly anisotropic 1D nanostructures. The GISAXS pattern analysis in the framework of the DistortedWave Born Approximation (DWBA) has been expanded to multilayered non-correlated surface science systems (non-correlated carbon nanotubes) and is based on the determination of carbon nanotubes density, characteristic lengths, atomic Co dispersion throughout the CNTs and roughnesses of the uncorrelated particles. Even dominated by envelope features of disordered objects, they provide noticeable information about CNTs films: both structural (orientation, size and length distribution) and correlation (density, mutual alignment) information. The results stand in rather good agreement with the Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) observations. Moreover, the GISAXS patterns could only be satisfactorily reproduced by adding a mixed C -Co contribution between the pure carbon and the metallic cobalt let on top of the CNT, inferring that cobalt continuously fills the nanotube in the course of the growth and that the CNTs experience a large tendency toward mutual alignment. The effect of variable X-ray incidence angles has been investigated. With a weak addition of ammonia (from 1% to 3% of the gas mixture) the density has been found to decrease by more than one order of magnitude.

Carbon nanotubes (CNTs) show exceptional properties which make them extremely attractive for many applications. The electronic structure of potassium adsorbed single-walled carbon nanotubes (SWCNTs) is investigated by x-ray near edge structure (XANES) spectroscopy. Gas molecules (H 2 O, O 2 , CO 2 , CO) and potassium (K) adsorbates showed non negligible sensitivity to the geometry, thermal annealing treatment, and hybridization. The SWCNT type is shown by transmission electron microscopy (TEM) whereas an aleatory arrangement of SWCNTs and the spherical iron particles along carbon nanotubes are observed by scanning electron microscopy (SEM). XANES shows that the charge transfer effect in K-doping SWCNTs increases the conductivity to 62.7%. The adsorption study demonstrates that the adsorption mechanism to remove potassium from aqueous solutions using SWCNTs is assimilated to the ion exchange process. The functional groups OH − , C=O and C≡C are involved in the adsorption process. They are correlated to the assignment of the adsorbates given by XANES.

We report on a quantitative Grazing Incidence Small Angle X-ray Scattering (GISAXS) study of the angular dependence of oriented carbon nanotubes (CNTs) grown by a catalytically activated, plasma direct current or plasma enhanced and hot filaments-assisted catalytic chemical vapour deposition (dc HF CCVD or PE HF CCVD) process. To synthesize these CNTs, some transition metal (TM) particles were used as a catalyst and dispersed on plain SiO2 (thickness 5 nm)/Si(100) substrates prior to the growth of CNTs. Some morphological (diameter, height) and disorder parameters have been determined using the GISAXS technique in the framework of Effective Layer Born Approximation (ELBA) and Distorted-Wave Born Approximation (DWBA) on noncorrelated multilayer systems. The GISAXS patterns, although dominated by envelope features of disordered islands, provide important complementary quantitative information about CNT films. The results are compared to scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. Furthermore, the GISAXS patterns could only be acceptably reproduced by considering an inter-mixing C–Co contribution and the metallic cobalt let on top of the CNT. While monitoring the incidence angle, we found that the disorder parameter decreases with increasing incidence angle, showing that the in-plane system order increases from the surface to the inner layers.

The ability to control the nanoscale shape of carbon nanostructures during wide-scale synthesis process is an essential goal in research for Nanotechnology applications. This paper reports a significant progress toward that goal. Variant CVD has been used for the synthesis of the samples studied. Curvature, hybridization and contamination are analyzed using Electron Microscopies and XANES spectroscopy. The investigations of the results show that four types of samples are obtained. They are carbon nanotubes (CNTs), carbon nanofibers (CNFs), carbon nanowalls (CNWs) and carbon nanoparticles (CNPs). Almost all of them have catalyst nanoparticles (metal) on top in top growth model or on base in base growth model and encapsulated or adsorbed in sidewalls. The orientation of tubular carbon nanomaterials depends on operating parameters. They are classified in three groups: the poorly oriented, the medium oriented and the highly oriented. Their contamination (radicals, atoms and molecules) and hybridization are intrinsically related to the curvature of their graphene layers. XANES spectroscopy allows quantitative characterization of nanomaterials.