XAS study of the orientation of oriented carbon nanotube films

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.