Absorption fine structure

EXAFS Extended X-ray absorption fine structure spectroscopy. A spectroscopic technique which can determine interatomic distances very precisely. 

EXAFS Extended x-ray absorption fine structure [177, 178] Variation of x-ray absorption as a function of x-ray energy beyond an absorption edge the probability is affected by backscattering of the emitted electron from adjacent atoms Number and interatomic distance of surface atoms... 

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). 

Lee P A, Citrin P H, Eisenberger P and Kincaid B M 1981 Extended x-ray absorption fine structure—its strengths and limitations as a structural tool Rev. Mod. Rhys. 53 769-806... 

Iwasawa Y (ed) 1996 X-Ray Absorption Fine Structure for Cataiysis and Surfaces (Singapore World Scientific)... 

Stdhr J, Kollin E B, Fischer D A, Flastings J B, Zaera F and Sette F 1985 Surface extended x-ray-absorption fine structure of low-Z adsorbates studied with fluorescence detection Rhys. Rev. Lett. 55 1468-71... 

Zaera F, Fischer D A, Carr R G and Gland J L 1988 Determination of chemisorption geometries for complex molecules by using near-edge X-ray absorption fine structure ethylene on Ni(IOO) J. Chem. Rhys. 89 5335-41... 

Ingalls R, Crozier E D, Whitmore J E, Seary A J and Tranquada J M 1980 Extended x-ray absorption fine structure of sodium bromide and germanium at high pressure J. Appl. Phys. 51 3158... 

Fischer D, Marti A and Hahner G 1997 Orientation and order in microcontact-printed, seif-assembied monoiayers of aikanethiois on goid investigated with near edge x-ray absorption fine structure spectroscopy J. Vac. Sc/. Technol. A 15 (4) 2173-80... 

Wu S, Lipkowski J, Tyiiszczak T and Hitchcock A P 1997 Eariy stages of copper eiectrocrystaiiization eiectrochemicai and in situ x-ray absorption fine structure studies of coadsorption of copper and chioride at the Au(111) eiectrode surface J.Phys. Chem. B 101 10 310-22... 

Rehr J J, Mustre de Leon J, Zabinski S I and Albers R C 1991 Theoretical x-ray absorption fine structure standards J. Am. Chem. Soc. 113 5135-40... 

Rehr J J, Albers R C and Zabinski S I 1992 High order multiple scattering calculation of x-ray absorption fine structure Phys. Rev. Lett. 69 3397-400... 

Figure 8.34 Experimental method for extended X-ray absorption fine structure (EXAFS)...

Figure 8.38 Curve fitting of Mo extended X-ray absorption fine structure (EXAFS) for Mo(SC6H4NH)3, taking into account (a) sulphur and (b) sulphur and nitrogen atoms as near neighbours. (Reproduced, with permission, trom Winnick, H. and Doniach, S. (Eds), Synchrotron Radiation Research, p. 436, Plenum, New York, 1980)...

Surface Extended X-Ray Absorption Fine Structure and Near Edge X-Ray Absorption Fine Structure (SEXAFS/NEXAFS)... 

This chapter contains articles on six techniques that provide structural information on surfaces, interfeces, and thin films. They use X rays (X-ray diffraction, XRD, and Extended X-ray Absorption Fine-Structure, EXAFS), electrons (Low-Energy Electron Diffraction, LEED, and Reflection High-Energy Electron Diffraction, RHEED), or X rays in and electrons out (Surfece Extended X-ray Absorption Fine Structure, SEXAFS, and X-ray Photoelectron Diffraction, XPD). In their usual form, XRD and EXAFS are bulk methods, since X rays probe many microns deep, whereas the other techniques are surfece sensitive. There are, however, ways to make XRD and EXAFS much more surfece sensitive. For EXAFS this converts the technique into SEXAFS, which can have submonolayer sensitivity. 

Alternatives to XRD include transmission electron microscopy (TEM) and diffraction, Low-Energy and Reflection High-Energy Electron Diffraction (LEED and RHEED), extended X-ray Absorption Fine Structure (EXAFS), and neutron diffraction. LEED and RHEED are limited to surfaces and do not probe the bulk of thin films. The elemental sensitivity in neutron diffraction is quite different from XRD, but neutron sources are much weaker than X-ray sources. Neutrons are, however, sensitive to magnetic moments. If adequately large specimens are available, neutron diffraction is a good alternative for low-Z materials and for materials where the magnetic structure is of interest. 

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