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Li and C 1s core-electron excitation spectra of electrochemically prepared stage-II and stage-I lithiated graphite were investigated by means of inelastic X-ray scattering spectroscopy. The near-edge structure is discussed, and the spectral features are interpreted using ab initio calculations. Our results confirm the invariance of the excitation threshold for transitions from C 1s core-states to empty pσ states upon Li intercalation for stage-I and show this invariance also occurs for the second stage of intercalation. A systematic shift of the rσ excitation threshold to lower energies with the Li content was observed. The Li core spectra reveal an ionic character of the intercalated Li in stage-I and in stage-II. The present results provide further valuable information for forthcoming in situ studies of lithiation/delithiation processes in graphite anodes by inelastic X-ray scattering spectroscopy. [ABSTRACT FROM AUTHOR]

Abstract: An experimental and theoretical study of electronic excitations in MgB2 covering the domain of large energy and momentum transfers is reported. Energy-loss spectra for several values of momentum transfers were measured in a polycrystalline sample by means of inelastic X-ray scattering spectroscopy. Ab initio calculations of the dielectric function as well as the energy-loss function were performed in the frame of the time-dependent local density approximation with inclusion of crystal local-field effects. We obtained very good agreement between the experimental and the theoretical energy dispersion of the peak maximum of the loss function. We found that crystal local-field effects are responsible for this agreement at large momenta. Fine structure observed in the measured spectra was interpreted in terms of strong interband transitions predicted by the calculations in the and directions. The theoretical dispersion of these features is in good accordance with the experimental data. Further spectral features in the measured spectra due to Mg 2s and 2p core electron excitations are also discussed. [Copyright &y& Elsevier]

A high-resolution spectrometer aimed at performing experiments of inelastic X-ray scattering by electronic excitations is described. The spectrometer has been installed at the D12A-XRD1 beamline of the National Synchrotron Light Laboratory (LNLS), in Campinas, Brazil. Synchrotron radiation is monochromated to about 6 kev and focused horizontally onto the sample by a sagittally focusing Si(lll) double-crystal monochromator in non-dispersive setting. The spectrometer operates in Rowland circle geometry and is based on a focusing Si(333) analyses in near-backdiffraction geometry for energy analysis of inelastically scattered photons. The analyses works at a fixed Bragg angle, so energy transfers are obtained by varying the incident photon energy. A relative energy resolution of the whole spectrometer of ∼1.5 x 10-4 at 5.93 kev has been achieved. As an example of application, inelastic X-ray scattering by plasmon excitation in polycrystalline Be was measured. Test results demonstrate that inelastic X-ray scattering experiments with eV energy resolution and an acceptable counting rate are feasible at the LNLS when focused on plasmon and particle-hole excitations. [ABSTRACT FROM AUTHOR]