Fourier transformation of EXAFS

Figure 2. Fourier transforms of EXAFS data of (a) the chloride salt of 1, (b) Mo/NaY, (c) sample (b) treated in flowing He at 373 K and (d) sample (b) treated in flowing He at 573 K.

Fig. 10 a Co K-edge XAS spectrum for CoP collected in transmission mode, showing the approximate regions where XANES and EXAFS features are observed and the assignment of dipolar and quadrupolar transitions, b EXAFS (x) vs. k curve, c Fourier transform of EXAFS... 

Figure 3. X-ray absorption data analysis of Fe EXAFS data for Rieske-like Fe S cluster. A) EXAFS data B) Fourier transform of EXAFS data showing peaks for Fe—S and Fe-Fe scattering. Thin vertical lines indicate filter windows for first and second shell.

Fig. 12a and b. Fourier transform of EXAFS data, and structure model for a 2.5 ML Pt/Si(lll) compared with a local (i.e. first and second shell) PtjSi configuration b PtSi silicide... 

Figure 1 shows Fourier transforms of EXAFS spectra of a few samples prepared. The radial distribution functions of these samples are different from that of nickel oxide or cobalt oxide [7]. All the Fourier transforms showed two peaks at similar distances (phase uncorrected) the peak between 1 and 2 A is ascribed to the M-0 bond (M divalent cation) and the peak between 2 and 3 A is ascribed to the M-O-M and M-O-Si bonds. The similar radial distribution functions in Figure 1 indicate that the local structures of X-ray absorbing atoms (Ni, Co, and Zn) are similar. No other bonds derived from metal oxides (nickel, cobalt and zinc oxides) were observed in the EXAFS Fourier transforms of the samples calcined at 873 K, which suggests that the divalent cations are incorporated in the octahedral lattice. 

Fourier transformation of EXAFS makes % k) a complex number, but often the FT is only represented by its amplitude, as shown in Figure 7.6. 

The radial distribution functions in Figure 7 represent the Fourier transform of EXAFS spectra. They display several peaks according to the nearest atomic shells surrounding the central Mn atoms. The first peak in the RDF allows the calculation of the Mn-O distance and the coordination number of the first shell. The second peak corresponds to the Mn-Mn distances. 

Fourier transformation of EXAFS data yields a function (R)... 

Figure 4.10 Effect of exposure of silica-supported ruthenium, ruthenium-copper, and copper catalysts to oxygen (1% oxygen in helium) at room temperature on the properties of the catalysts, as shown by Fourier transforms of EXAFS data at 100°K on the catalysts in the absence and presence of oxygen (31). (Transforms in the upper half of figure are for ruthenium EXAFS transforms in lower half are for copper EXAFS.) (Reprinted with permission from the American Institute of Physics.)...

Fig. 7. Fourier transform of EXAFS signal x( ) The reduction of Cu II) species to metallic Cu clusters starts with the bottom graph (rehydrated sample). For comparison see the FT of a Cu foil reference spectrum (dotted).

Figure 3. The radial distribution function (RDF) obtained from the Fourier transformation of EXAFS spectra for the underexchanged Cu-ZSM-5-59 (a) sample has been exposed to ambient air after ion exchange and calcination (b) sample was oxidized in dry air at 773 K and was cooled in dry air to room temperature (c) sample was auto-reduced in ultra-high purity He at 773 K and was cooled to room temperature in He.

At the present time, of all EXAFS-like methods of analysis of local atomic structure, the SEES method is the least used. The reason is that the theory of the SEES process is not sufficiently developed. However the standard EXAES procedure of the Fourier transformation has been applied also to SEES spectra. The Fourier transforms of MW SEES spectra of a number of pure 3d metals have been compared with the corresponding Fourier transforms of EELFS and EX-AFS spectra. Besides the EXAFS-like nature of SEES oscillations shown by this comparison, parameters of the local atomic structure of studied surfaces (the interatomic distances and the mean squared atomic deviations from the equilibrium positions [12, 13, 15-17, 21, 23, 24]) have been obtained from an analysis of Fourier transforms of SEES spectra. The results obtained have, at best, a semi-quantitative character, since the Fourier transforms of SEES spectra differ qualitatively from both the bulk crystallographic atomic pair correlation functions and the relevant Fourier transforms of EXAFS and EELFS spectra. 

Figure 19.4 XAFS (XANES and Fourier transforms of EXAFS) spectra of Ti/Si binary oxide thin films. Ti02 content (%) (a. A) 6.6, (b, B) 9.5, and (c, C) 50.1...

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