XAFS

For bulk structural detemiination (see chapter B 1.9). the main teclmique used has been x-ray diffraction (XRD). Several other teclmiques are also available for more specialized applications, including electron diffraction (ED) for thin film structures and gas-phase molecules neutron diffraction (ND) and nuclear magnetic resonance (NMR) for magnetic studies (see chapter B1.12 and chapter B1.13) x-ray absorption fine structure (XAFS) for local structures in small or unstable samples and other spectroscopies to examine local structures in molecules. Electron microscopy also plays an important role, primarily tlirough unaging (see chapter B1.17). 

From the above descriptions, it becomes apparent that one can include a wide variety of teclmiques under the label diffraction methods . Table Bl.21.1 lists many techniques used for surface stmctural detemiination, and specifies which can be considered diffraction methods due to their use of wave interference (table Bl.21.1 also explains many teclmique acronyms commonly used in surface science). The diffraction methods range from the classic case of XRD and the analogous case of FEED to much more subtle cases like XAFS (listed as both SEXAFS (surface extended XAFS) and NEXAFS (near-edge XAFS) in the table). 

EXAFS is part of the field of X-ray absorption spectroscopy (XAS), in which a number of acronyms abound. An X-ray absorption spectrum contains EXAFS data as well as the X-ray absorption near-edge structure, XANES (alternatively called the near-edge X-ray absorption fine structure, NEXAFS). The combination of XANES (NEXAFS) and EXAFS is commonly referred to as X-ray absorption fine structure, or XAFS. In applications of EXAFS to surface science, the acronym SEXAFS, for surface-EXAFS, is used. The principles and analysis of EXAFS and SEXAFS are the same. See the article following this one for a discussion of SEXAFS and NEXAFS. 

XAFS V, Proceeding of the Fifth International Conference on X-ray Absorption Fine Structure. (J. M. de Leon, E. A. Stern, D. E. Sayers, Y. Ma, and J. J. Rehr, eds.) North-Holland, Amsterdam, 1989. Also in Physica B. 158, 1989. Report of the International Workshop on Standards and Criteria in X-ray Absorption Spectroscopy (pp. 701-722) is essential reading. 

The experiments were performed at the energy dispersive absorption beam line of the DCI ring at LURE. In figure 1 we have plotted the XAFS and XMCD signals at the nickel K-edge. 

Figure 1. Thin line experimental XAFS at Ni K-edge in CsNi[Cr(CN)J,2H20 Thick line experimental XMCD spectra at Ni K-edge in CsNi[Cr(CN)gl,2H20...

XAFS (EXAFS and XANES) methods X-ray diffraction method Biological investigations Flydrolysis of [OrganotinllV)]" Cations Interactions of [OrganotinllV)]" with Biological Molecules... 

The X-ray absorption fine structure (XAFS) methods (EXAFS and X-ray absorption near-edge structure (XANES)) are suitable techniques for determination of the local structure of metal complexes. Of these methods, the former provides structural information relating to the radial distribution of atom pairs in systems studied the number of neighboring atoms (coordination number) around a central atom in the first, second, and sometimes third coordination spheres the... 

Figure 1. Schematic diagram of polarization-dependent total-reflection fluorescence XAFS.

Ylwasawa (ed.). X-ray Absorption Fine Structure(XAFS) for Catalysts and Surfaces, World Scientific, Singapore, 1996. 

Dynamic Structural Change of Pd Induced by Interaction with Zeolites Studied by Means of Dispersive and Quick XAFS 427... 

---