X-ray emission studies of the valence band of nanodiamonds annealed at different temperatures

X-ray emission spectroscopy has been applied to examine the electronic stru cture of onion-ne carbon (OLC) generated by the annealing treatment of nano diamonds (ND). The C K alpha spectra of OLC produced in the temperature ran ge of 1600-1900 K were found to be markedly different from the spectrum of particles formed at 2140 K and to be characterized by better ordering of gr aphitic shells. The latter spectrum was shown to be very similar to the C K alpha of polycrystalline graphite, while the former ones exhibited a signi ficant increase of the high-energy maximum that might be caused by the defe ct structure of graphitic networks forming at the intermediate temperatures . The experimental spectra were compared with the theoretical spectra from quantum-chemical semiempirical AM1 calculation of several models: a fullere ne molecule, C-240, having icosahedral structure, a C-240 molecule incorpor ating a greater number of nonhexagonal rings, and a holed structure formed by removing pentagons from the icosahedral molecule. The density of high-en ergy electronic states in the valence band of the graphitic cage was found to be practically invariant to a change in ring statistics but to significa ntly increase because of localization of electrons on the zigzag sites of a hole boundary.