Band-structure and core-hole effects in resonant inelastic soft-x-ray scattering: Experiment and theory

Inelastic x-ray scattering has been observed in the hexagonal forms of carb on (graphite) and boron nitride (hBN), both above and below their K edges. For excitation energies below the core threshold, inelastic-loss features a re observed, which disperse linearly with excitation energy (Raman-like beh avior). However, above the threshold, emission features that move in a nonl inear fashion are observed. We show that these two scattering regimes, whic h have previously been thought of as separate processes, viz,, resonant x-r ay Raman scattering (below threshold) and resonant inelastic x-ray scatteri ng (above threshold), are described by the same theory for resonant fluores cence. Simulated spectra, with and without excitonic effects, are presented and compared with experiment. We conclude, based on this comparison, that excitonic effects influence these spectra in two ways. Primarily, the total fluorescence yields are enhanced or reduced simply because of changes in t he absorption cross sections. Second, excitonic effects on emission feature s can be pronounced near some excitonic resonances, and these changes are m ore significant for excitation further above the K edges, which we attribut e to the multiplicity of core-excited states being probed. Based on these f indings, we conclude that core-hole effects do not necessarily undermine an interpretation of the scattering in terms of a one-electron (noninteractin g) picture, and that resonant fluorescence spectroscopy may be successfully used to probe the band structure of solids. [S0163-1829(99)08911-0].