Multiple-scattering approaches to carbon K-shell near-edge X-ray absorption fine structure of graphite

Abstract

The multiple-scattering cluster method was first employed to calculate the theoretical near-edge X-ray absorption fine structure (NEXAFS) spectrum of graphite. Studies on the polarization dependence on the incident vector E classify spectral features into pi and sigma resonances. Characterization of the carbon K-shell NEXAFS spectra of the species modelled by both a single layer and a multilayer has been performed. It reveals that a pi * resonance originally located at around 989 eV splits with the accumulation of the number of atoms included in the cluster. Multilayer calculation has little influence on the NEXAFS spectrum. Our calculation coincides with the experimental results fairly well. In addition, it has been found to be in good agreement with the final density of states derived from band-structure calculations.

Oscillations in the Photoionization Cross Section ofC60

“…Model B, despite being quite simple, is a more realistic one than model A, yet agrees equally well with the experimental results of Benning et al [3] and Wu et al [4]. Also, the potential parameters used in model B have reasonable values compared to the muffin-tin potential for carbon solids [9]. This seems to indicate that our conclusion regarding the origin of the variation of the photoemission partial cross section is, in principle, correct.…”

“…(8) one has to assign the potential parameters. Based on the muffin-tin potential used for carbon solids [9], the average half thickness of the deep potential shell containing the carbon atoms is estimated to be about d 0.5 Å, and the shallow potential in the hollow space to be 2U 00 27.2 eV. The remaining deep potential parameter U 0 is then adjusted to give a best fit to the six final state experimental energies at the photoemission cross section minima.…”

Nanoscale characterization of aircraft soot: A high-resolution transmission electron microscopy, Raman spectroscopy, X-ray photoelectron and near-edge X-ray absorption spectroscopy study

“…A second continuum of  symmetry starts above 291 eV, beginning with a sharp excitonic resonance at 291.8 eV [55], [56] followed by a * transition at 292.9 eV, a shape resonance related to the electron singlescattering between two adjacent carbons in the graphite hexagons [50], [57]. The series of broad resonances above 295 eV can be alternatively understood as excitations to high energy bands of the empty density of states (DOS) of graphite [50], [51] or as electron multiplescattering resonances within the carbon lattice of the graphene layer [58]. It is noteworthy that the NEXAFS spectrum of graphite is very close to that of substrate-decoupled graphene [59] and single-wall nanotubes [54], indicating that interlayer interactions have a negligible contribution in the spectrum of graphite.…”

Theoretical and experimental study of the graphite 1sx-ray absorption edges

“…This conclusion was contradicted by Weng et al, 26 who argued that the ground-state DOS accurately models the XAS spectrum, and whose arguments were used to explain newer experimental data. 14 Recent multiple scattering calculations give support to the results of Weng et al, 27 whereas a recent perturbation theoretical treatment of XAS and inelastic x-ray scattering used the assumption that core-hole effects were important, with reasonable success, 28 but came to no conclusions about the relative accuracy in describing experimental data after including core-hole effects. More recently another experimental probe, core level autoionization, 17 has given evidence that the original conclusion of Mele and Ritsko is correct, i.e., that the * threshold in graphite is strongly affected by excitonic effects.…”