EXAFS spectroscopy: a new method for structural investigation

Abstract

Abslracl. W e have measured the pressure effects on the superconducting T, and the current density/, of the YBaCuO (123) phase and the BiSrCaCuO (2223) phase up to 10 kbar. We have found that for Bi ceramics the increase in J , with pressure is related to the T, change, while for YBCO it is due to the Josephson medium weak-link eflects. This result provides the evidence that in Bi compounds strongcurrent Josephson contacts are possible. The influence of high magnetic fields on the Josephson critical current is briefly discussed.

X-ray absorption spectroscopy study on SiC-side interface structure of SiO2–SiC formed by thermal oxidation in dry oxygen

“…The interatomic distance for the first nearest neighbor is obtained with an accuracy of 0.01 Å. 32) The peak positions of the first and second nearest neighbors, at 1.5 and 2.6 Å, respectively, for the Si-face agree with those for the SiC bulk, as shown in Fig. 4(a).…”

Atomic and Electronic Structure of Metal–Salen Complexes [M(Salen)], Their Polymers and Composites Based on Them with Carbon Nanostructures: Review of X-ray Spectroscopy Studies

“…Studies of EXAFS spectra with the energy region of EXAFS oscillations from 30 to ∼1500 eV above the absorption edge allows one to determine with sufficiently high accuracy distances and coordination numbers around a specific absorbing atom, thus providing probing of the local atomic structure of a polyatomic system near the absorbing atom (Figure 11a) [128]. At present, it can be considered clear that the main features of the EXAFS structure are caused by the processes of elastic scattering of a photoelectron wave by the potential relief of the nearest neighborhood of the absorbing atom in a polyatomic system [129,130]. This primary wave is scattered by neighboring atoms through acts of single backscattering of electrons and generates scattered waves that can interfere (constructively or destructively) with the primary wave (see Figure 12), which leads to the appearance of EXAFS oscillations [129].…”

“…where k is the wave number of the photoelectron wave, f j (k) is the amplitude of the backscattered electron wave by atoms of the coordination sphere, δ j (k) are phase shifts, N j is the number of neighboring atoms to atom j, R j is the distance to atom j, and σ j 2 is the Debye-Waller factor, characterizing the root mean square amplitude of the deviation of the distance to atoms of type j from the average value caused by structural and thermal disorder [130].…”

“…In view of the above, EXAFS spectroscopy is most often used to obtain primary structural information about new chemical compounds (chemical bond lengths, coordination numbers, and type of atoms surrounding the studied one) within the range of 4-5 Å (the first few coordination spheres). In this case, EXAFS spectroscopy is usually implemented for the 1s and 2p shells of elements with a charge number Z > 20 [128,130].…”

“…where k is the wave number of the photoelectron wave, fj(k) is the amplitude of the backscattered electron wave by atoms of the coordination sphere, δj(k) are phase shifts, Nj is the number of neighboring atoms to atom j, Rj is the distance to atom j, and σj 2 is the Debye-Waller factor, characterizing the root mean square amplitude of the deviation of the distance to atoms of type j from the average value caused by structural and thermal disorder [130]. In order to separate the contributions of individual coordination spheres from the overall function χ(k), spectral analysis methods are used by expansion of the function χ(k) into a Fourier integral (see Figure 13).…”