The x-ray fluorescence and absorption of highly oriented pyrolytic graphite have been measured using monochromatic synchrotron radiation. The spectra can be separated into contributions from~and oband components by measuring at different angles of incidence and at different emission angles. The shape of the x-ray fluorescence spectra varies dramatically with excitation energy near the C E edge.This dependence on excitation energy can be interpreted within a resonant-inelastic-scattering formalism. The results are compared with previously published band-structure calculations and photoemission results, and demonstrate the potential for using x-ray fluorescence to obtain symmetry-resolved band information.

X-ray fluorescence spectroscopy with monochromatic photon excitation is presented as a tool for studies of charge-transfer excitations in correlated systems, using CeO 2 and UO 3 as examples. Ce 4f ! 3d and U 5f ! 3d x-ray fluorescence, with excitation near the 3d thresholds, probes states as eigenvalues for the ground state Hamiltonian from the Anderson impurity model. Sweeping the excitation energy across 3d absorption edges enhances contributions of different electronic configurations to fluorescence so that observed resonances indicate the charge-transfer origin of the absorption satellites. [S0031-9007 (96)00691-6] PACS numbers: 78.70.En, 71.27. + a, 71.28. + d, 78.70.DmA degree of localization of the f states which can have both bandlike and localized character is a key point in the description of the electronic structure of rare-earth and actinide systems. While delocalized models based on band theory were proposed to explain ground state [1] and spectroscopic [2] properties, various transport and spectroscopic signs of electron correlation effects are observed even in "itinerant" materials and cannot be fully interpreted within one-electron formalism. As an alternative, localized approach the Anderson impurity model (AIM) is often used [3,4] which treats the f states of a rare-earth or actinide atom as a degenerate impurity level hybridized with the valence band, but neglects the interaction between f levels on different atoms. To describe the ground state, a model Hamiltonian is constructed which includes as parameters the energy of a localized state´f , delocalized states´y, the hybridization strength V , and the on-site f-f Coulomb interaction U ff . The parameters are optimized by fitting both high-energy spectroscopic and low-energy thermodynamic data [3]. However, these parameters may be renormalized in a different way in high-versus lowenergy experiments [5,6]. In this case, those experimental techniques become attractive which can be related to both high-energy and low-energy scale techniques such as valence band resonant x-ray fluorescence spectroscopy (RXFS). In the localized, many-body approach, RXFS is expected to probe the states as eigenvalues of the ground state Hamiltonian via creation or annihilation of a core or hole due to site and symmetry selectivity of RXFS. In this Letter, we explore a potential of RXFS in studies of so-called mixed-valency compounds where the anion 2p ! metal f charge-transfer excitations play an impor-tant role and the ground state can be described as a strong mixture of several electronic configurations. Using CeO 2 [4,7-11] and UO 3 [12-15] as systems with strong metal f O 2p hybridization we demonstrate that the localized, many-body approach is appropriate for the description of the resonant x-ray fluorescence (RXF) process and that RXF spectra can be interpreted within the framework of the AIM. We show that it is essential to include the RXF data in spectroscopic analysis for these systems in order to derive a unique set of model parameters.The measurements on...

Polarization-dependent x-ray absorption measurements were performed on crystalline ZnO three-dimensional arrays consisting of highly oriented microrods as well as on particulate thin films consisting of monodisperse spherical nanoparticles. Strong anisotropic effects have been observed for the highly oriented ZnO rods, but not for the isotropic spherical nanoparticles. Full-potential calculations of the orbital-resolved x-ray absorption of a ZnO wurtzite periodic crystal, including Zn 3d among the valence states, show very good agreement with the experimental findings. Comprehensive fundamental knowledge of the electronic structure of ZnO is obtained by probing and demonstrating the orbital symmetry of oxygen and its contribution to the conduction band of this important II–VI semiconductor.