XAS study of the orientation of oriented carbon nanotube films

Abstract

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.

Curvature, Hybridization and Contamination of Carbon Nanostructures Analysis Using Electron Microscopy and XANES Spectroscopy

“…This ratio calculated in Tables 2 and 3 for some CNTs samples is indicative of the orientation tendency of the graphite orbitals [22] and as consequence, the graphene layer's.…”

“…The curvature of the graphite sheet is also among those factors that were considered to explain the change of the electronic states in CNSs [36]. The carbon K-edge x-ray absorption spectroscopy [21,37,38] and TEM [21,22] revealed that the features of electronic states of the carbon atoms in the carbon nanostructures are very similar to those of graphite. Thus, the CNSs XANES spectra are very similar to those of graphite and almost identical with that of HOPG (High Oriented Pirolytic Graphite) measured at the magic angle (54.7˚), where no polarization dependence of π-type states occurs.…”

“…These main features of each CNS spectrum can be summarized in tables, as XANES spectra of CNTs in Tables 2 and 3 for normal incidence and grazing incidence respectively. There are some non-intrinsic features in XANES spectra, some disappeared or became weak after thermal annealing, among them are P, P' and P" resulting on potassium contamination [22,26]. This potassium present in samples might come from the beam line on the synchrotron station.…”

“…As a consequence of this specific dimensional particularity, every nanostructure synthesized has to be characterizing for fully mastering its proprieties and by the way, handle its applications [18][19][20][21][22]. Another specificity of nanostructures is their complex and heavy synthesis processes compared to other materials used in different domains of technology and their different methods of synthesizing [23][24][25].…”

A novel combined experimental and multiscale theoretical approach to unravel the structure of SiC/SiOx core/shell nanowires for their optimal design

“…49,50 The latter, in particular, revealed to be a powerful tool for investigating nanostructured materials and inner interfaces. 6,51 However, state-of-the-art computational investigations are limited to the crystalline phases of SiC nanowires, [52][53][54][55][56] while the SiC/SiO x interface is modeled only in the case of geometries as slabs or nanodots. 57,58 Furthermore, these models are not enough accurate and realistic for shedding light on the many electronic and structural information enclosed in XANES spectra, and to explain the absorption peak lineshape of several transitions arising from these structures.…”