The linearly polarized Cu L3-edge x-ray-absorption near-edge structure (XANES) of Bi2Sr2CaCu208+z has been measured and the spectra are interpreted by the full multiple-scattering approach in real space.The polarized spectra over a range of 20 eV can be predicted in terms of the one-electron dipole (Al =+1)transition Cu 2p~ed, probing the unoccupied d-like (1=2) density of states projected on the Cu site with orbital angular momentum m& =0, 1 in the E~~z spectra, and the mI=2, 1, and 0 in the Elc spectra. The oscillator strength for the dipole allowed transitions (Al = -1) Cu 2p~v s is shown to be a factor of 100 weaker than the 2p~3d transitions. The Coulomb interaction in the final state between the Cu 2p core hole and the excited Cu 3d electron is found to be 5.5 eV forming a bound state below the continuum threshold, the well-known Cu L3 white line. On the contrary, the core hole induces a nearly rigid redshift about 1 eV of the high-energy conduction bands.

The local atomic structure of an amorphous NiZr2 alloy was investigated using the anomalous wide-angle x-ray scattering (AWAXS), differential anomalous scattering (DAS) and reverse Monte Carlo (RMC) simulations techniques. The AWAXS measurements were performed at eight different incident photon energies, including some close to the Ni and Zr K edges. From the measurements eight total structure factor S(K, E) were derived. Using the AWAXS data four differential structure factors DSFi(K, Em, En) were derived, two about the Ni and Zr edges. The partial structure factors SNi-Ni(K), SNi-Zr(K) and SZr-Zr(K) were estimated by using two different methods. First, the S(K, E) and DSFi(K, Em, En) factors were combined and used in a matrix inversion process. Second, three S(K, E) factors were used as input data in the RMC technique. The coordination numbers and interatomic distances for the first neighbors extracted from the partial structure factors obtained by these two methods show a good agreement. By using the three-dimensional structure derived from the RMC simulations, the bond-angle distributions were calculated and they suggest the presence of distorted triangular-faced polyhedral units in the amorphous NiZr2 structure. We have used the Warren chemical short-range order parameter to evaluate the chemical short-range order for the amorphous NiZr2 alloy and for the NiZr2 compound. The calculated values show that the chemical short-range order found in these two materials is similar to that found in a solid solution.

The linearly polarized Cu K-edge x-ray-absorption near-edge structure (XANES) of Bi~Sr2CaCu20g+g (Bi 2:2:1:2)has been measured, and the spectra are interpreted by the multiple-scattering approach in real space. The polarized spectra can be predicted in terms of a one-electron dipole (hl =+1)transition Cu 1s~ep, probing the unoccupied p-like (l = 1) density of states projected on the Cu site with orbital angular momentum m, =O in the E~~z spectra, and the m&=1 in the Etc spectra. Therefore we show that the electronic structure of the high-energy conduction bands, beyond the Cu 3d band, are well described in terms of the one-electron approximation. Final-state eItects induced by the core hole have been studied and calculated. A satellite 7 eV above the main K-XANES peak in both polarizations is shown to be a multielectron shake-up excitation, and it is enhanced going into the insulating phase. Structural information on the copper site in Bi2Sr2CaCu208+z and in Bi2Sr2YCu208+z has been extracted from XANES spectra, providing evidence for the decrease of the Cu-0 distance in the metallic phase.

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A two-and, alternatively, a four-crystal monochromator were used for simultaneous measurements of the profiles backward (h) and forward (o) diffracted by a thin Si (111) crystal plate for diffraction angles up to exactly 90 ° at DCI-LURE (Orsay). It is shown that the set-up with a four-crystal monochromator allows the characterization of the back-diffraction region for any crystal plate reflection. Asymmetry and full width at half-maximum (FWHM) of the experimental backwarddiffraction profiles are analyzed. Possible simultaneous diffractions occurring near 90 ° incidence, giving extra peaks in the forward-diffracted profiles, are studied. The good contrast of the o-beam profiles suggests that the back-diffracted o beam could be used as a highly monochromatic beam.