TITLE:
Theoretical Investigation of X-Ray Absorption near Edge Spectroscopy (XANES) Angular Dependence of Aligned Carbon Nanotubes Grown by DC HF CVD Process
AUTHORS:
Bridinette Thiodjio Sendja, Rolant Eba Medjo, Jeannot Mane Mane, Germain Hubert Ben-Bolie, Pierre Owono Ateba
KEYWORDS:
Angular Dependence, XANES, Normal Incidence, Grazing Incidence, Carbon Nanotubes, Intensity
JOURNAL NAME:
Materials Sciences and Applications,
Vol.6 No.5,
May
12,
2015
ABSTRACT: Carbon nanotubes (CNTs) grown on plain substrates SiO2/Si(100) by a direct current and hot filaments
catalytic chemical vapor deposition process have been studied by synchrotron X-ray absorption
near edge spectroscopy (XANES) technique to theoretically investigate the angular-dependence
of carbone (C) K-edge π* and σ* transitions. Experimental XANES spectra show that π*
resonance increases with the incidence angle from normal to grazing incidence angle while σ* resonance
decreases. This has been explained by the sine-square and cosine-square dependencies of
π* and σ* intensities, respectively. These results were confirmed by theoretical XANES curves of
highly oriented pyrolytic graphite (HOPG) and CNTs plotted versus incidence angle. It has been
shown that π* and σ* transitions strongly depend on the nature of polarized light (linearly or circularly).
At the linear polarized light, π* resonance is a preference as well as at right-circular polarized.
At the left-circular polarized light, σ* resonance is a preference. The π* intensities are high at
parallel orientation and the σ* intensities are low at normal orientation. The smallest π* intensity
is noticed at normal orientation, where the π* orbitals are supposed to be lying parallel to the surface
plane for perfectly aligned HOPG or CNTs. This explains the incomplete extinction of π* intensity.
We noticed at parallel orientation a region where any π* and σ* transitions did not expect because
of the lack of polarization light.