Soft X-ray spectroscopy and quantum chemistry characterization of defects in onion-like carbon produced by nanodiamond annealing

The electronic structure of onion-like carbon (OLC) consisted of quasi-spherical and polyhedral nanoparticles and produced as a result of nanodiamond annealing at 1800 K and 2140 K has been probed by soft X-ray emission and X-ray absorption spectroscopy. The enhanced density of states in the vicinity of the Fermi level was revealed for OLC prepared at moderate temperature. Ab initio calculation on carbon models showed the only unpaired electrons at the zigzag edges of graphitic fragments can provide localized states observed in the X-ray spectra. With the increase of the annealing temperature the defects, which likely constitute the boundaries of incompletely closed onion shells, are healing. (c) 2006 Elsevier B.V. All rights reserved.