The extended x-ray absorption fine structure (EXAFS) has been measured at both the K edges of cadmium and tellurium in CdTe, from liquid helium to room temperature, in order to investigate the local thermodynamic behaviour. The temperature dependences of the structural parameters obtained from the separate analysis of the two edges are perfectly consistent. The positive contribution to the thermal expansion due to the bond stretching and the negative contribution due to the tension effects are disentangled and quantified in terms of the bond thermal expansion and the perpendicular mean square relative displacement. The comparison with previous EXAFS results for Ge and CuCl shows that relevant correlations can be established between a number of local parameters measured by means of EXAFS and the properties of the lattice negative thermal expansion of tetrahedrally bonded semiconductors. The effective force constants derived from the EXAFS are compared with the force constants of a valence force field model.

The evaluation of uncertainty in temperature-dependent EXAFS measurements is discussed, considering the specific case of a recent experiment performed on CdTe. EXAFS at both Cd and Te K-edges was measured at different times and at different beamlines in a temperature range from 5 to 300 K. Attention is focused on the nearest-neighbours parameters: bond thermal expansion, parallel and perpendicular mean-square relative displacements and the third cumulant. Different causes of uncertainty, a comparison of experimental results with theoretical models, the difference between EXAFS and crystallographic thermal expansions and the meaning of the third cumulant are discussed.

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.

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.