X-ray spectroscopy characterization of carbon nanotubes and related structures

X-ray emission spectroscopy was applied for revealing the peculiarities in the electronic structure of different carbon nanotubes. The CKalpha-spectra of graphite and arc-produced multiwall carbon nanotubes (MWNTs) were shown to be similar in appearance indicating essentially no difference in the electronic state of carbon atoms constituting both materials. Slight changes detected in the spectrum of arc-produced single-wall carbon nanotubes (SWNTs) were attributed to the pi-system perturbation due to curvature of small diameter graphite shells. The CKalpha-spectrum of catalytic MWNTs showed the enhanced density of high-energy states that by the results of quantum-chemical calculations on various tube models could be caused by development of vacancies in the tube walls. The angular dependence of X-ray fluorescence from the samples of the oriented MWNTs was compared with that measured for graphite. The dependence can be used for qualitative characterization of tube alignment and definition of the width of occupied pi-band and defect structure of graphitic materials.