Carbon K-shell near edge structure calculations of graphite using the multiple scattering approach

The ability of electron energy loss spectroscopy (EELS) to accurately determine chemical compositions from inner-shell loss edges is well known. In addition to elemental concentrations, each characteristic absorption edge exhibits structure which provides information on the atomic environment of the absorbing atom. The strong oscillations which occur within about 40 eV of the Fermi energy as known as near edge structure (NES) and reflect the local density of unoccupied states. In the present work, the near edge absorption fine structure of carbon in graphite has been calculated using the multiple scattering approach. The effects of both a neutral carbon absorber and taking into account the effect of the core hole by using a nitrogen (Z+1) absorber atom are considered. The best agreement with experiment was obtained for the case of the nitrogen absorber and a cluster of 150 atoms, with the calculated NES containing the main features observed experimentally. A splitting near the onset of the σ* peak similar to that seen experimentally, was found to occur in the calculated NES for one of the two in equivalent carbon atoms in the graphite structure. This splitting was not observed in the calculated NES for a single sheet of graphite supporting the proposition that it only occurs in well ordered graphite. This result supports the proposition that the splitting originates from a sharp σ* peak and a dipole allowed bandlike contribution associated to the Γ2- branch of the free-electron-like interlayer states