By Boon K. Teo
The phenomenon of prolonged X-Ray Absorption superb constitution (EXAFS) has been recognized for it slow and used to be first taken care of theoretically via Kronig within the Thirties. fresh advancements, initiated through Sayers, Stern, and Lytle within the early Nineteen Seventies, have resulted in the popularity of the structural content material of this method. while, the provision of synchrotron radiation has significantly more suitable either the purchase and the standard of the EXAFS info over these accessible from traditional X-ray resources. Such advancements have confirmed EXAFS as a robust software for constitution stories. EXAFS has been effectively utilized to a variety of major clinical and technological structures in lots of varied fields resembling inorganic chemistry, biochemistry, catalysis, fabric sciences, and so on. this can be very priceless for structures the place single-crystal diffraction ideas are usually not with no trouble appropriate (e.g., fuel, liquid, resolution, amorphous and polycrystalline solids, surfaces, polymer, etc.). although the EXAFS process and purposes have matured enormously during the last decade or so, no introductory textbook exists. EXAFS: easy ideas and knowledge research represents my modest try to fill this kind of hole. during this publication, I target to introduce the subject material to the amateur and to aid alleviate the confusion in EXAFS information research, which, even if changing into increasingly more regimen, remains to be a slightly tough activity and will, every now and then, discourage the beginners.
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Additional resources for EXAFS: Basic Principles and Data Analysis
Qualitative rationalization of the absence and presence, respectively, of EXAFS in a monatomic gas such as Kr (a and c) and a diatomic gas such as Br2 (b and d). Figures (a) and (b) are taken from the work of Kincaid and Eisenberger (1975). 3) In order to relate x(E) to structural parameters, it is necessary to convert the energy E into the photoelectron wavevector k via Eq. 2. 4) J Here F j (k) is the backscattering amplitude from each of the N j neighboring atoms of the jth type with a Debye-Waller factor of Uj (to account for thermal vibration (assuming harmonic vibration) and static disorder (assuming Gaussian pair distribution) and at a distance rj away).
This assumption is generally valid if one considers that multiple scattering processes can be accounted for by adding all scattering paths that originate and terminate at the central atom (absorber). Each of these processes then behaves like sin (2kr eff) where 2r elf is the total scattering path length which is much larger than that of the direct backscattering from the nearest neighbors. Thus, multiple scattering will give rise to rapidly oscillatory waves in k space which tend to cancel out.
2b and d). the outgoing photoelectron can be backscattered from the neighboring atoms thereby producing an incoming wave which can interfere either constructively or destructively with the outgoing wave near the origin, resulting in the oscillatory behavior of the absorption rate (cf Fig. 2b). I. vs E depends on the type (and bonding) of the neighboring atoms and their distances away from the absorber, respectively. This simple picture of EXAFS has been formulated into the generally accepted short-range single-electron single-scattering theory (Stern, 1974; 1/ I Stern, Sayers, and Lytle, 1975; Ashley and Doniach, 1975; Lee, et ai, 1975, 1977).
EXAFS: Basic Principles and Data Analysis by Boon K. Teo