Surface-extended X-ray absorption fine structure spectroscopy

SEXAFS — Surface-extended X-ray absorption fine structure (spectroscopy), a modified form of -> EXAFS adopted to the needs of surface and interfacial science for details see - EXAFS. 

In its surface sensitive adaptation, the method is called SEXAFS (surface extended X-ray absorption fine structure spectroscopy). 

S)EXAFS (Surface) Extended X-ray Absorption Fine Structure (Spectroscopy)... 

ARUPS) for the valence DOS features, and X-ray photoelectron spectroscopy (XPS) for the energy shift of a core band. Surface extended X-ray absorption fine-structure spectroscopy (SEXAFS) and impact-collision ion-scattering spectroscopy (ICISS) are also commonly used in the chemisorption studies. 

SEXAES Surface extended X-ray absorption fine-structure spectroscopy... 

All analytical methods that use some part of the electromagnetic spectrum have evolved into many highly specialized ways of extracting information. The interaction of X-rays with matter represents an excellent example of this diversity. In addition to straightforward X-ray absorption, diffraction, and fluorescence, there is a whole host of other techniques that are either directly X-ray-related or come about as a secondary result of X-ray interaction with matter, such as X-ray photoemission spectroscopy (XPS), surface-extended X-ray absorption fine structure (SEXAFS) spectroscopy, Auger electron spectroscopy (AES), and time-resolved X-ray diffraction techniques, to name only a few [1,2]. 

Electrons Auger Electron Spectroscopy, Extended X-Ray Absorption Fine Structure, Low-Energy Electron Diffraction, Scanning Electron Microscopy, Surface Extended X-Ray Absorption Fine Structure, Ultraviolet Photoelectron Spectroscopy, X-Ray Absorption Near Edge Fine Structure, and X-Ray Photon Spectroscopy. 

Another contribution to variations of intrinsic activity is the different number of defects and amount of disorder in the metallic Cu phase. This disorder can manifest itself in the form of lattice strain detectable, for example, by line profile analysis of X-ray diffraction (XRD) peaks [73], 63Cu nuclear magnetic resonance lines [74], or as an increased disorder parameter (Debye-Waller factor) derived from extended X-ray absorption fine structure spectroscopy [75], Strained copper has been shown theoretically [76] and experimentally [77] to have different adsorptive properties compared to unstrained surfaces. Strain (i.e. local variation in the lattice parameter) is known to shift the center of the d-band and alter the interactions of metal surface and absorbate [78]. The origin of strain and defects in Cu/ZnO is probably related to the crystallization of kinetically trapped nonideal Cu in close interfacial contact to the oxide during catalyst activation at mild conditions. A correlation of the concentration of planar defects in the Cu particles with the catalytic activity in methanol synthesis was observed in a series of industrial Cu/Zn0/Al203 catalysts by Kasatkin et al. [57]. Planar defects like stacking faults and twin boundaries can also be observed by HRTEM and are marked with arrows in Figure 5.3.8C [58],... 

Surface analytical techniques. A variety of spectroscopic methods have been used to characterize the nature of adsorbed species at the solid-water interface in natural and experimental systems (Brown et al, 1999). Surface spectroscopy techniques such as extended X-ray absorption fine structure spectroscopy (EXAFS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) have been used to characterize complexes of fission products, thorium, uranium, plutonium, and uranium sorbed onto silicates, goethite, clays, and microbes (Chisholm-Brause et al, 1992, 1994 Dent et al, 1992 Combes et al, 1992 Bargar et al, 2000 Brown and Sturchio, 2002). A recent overview of the theory and applications of synchrotron radiation to the analysis of the surfaces of soils, amorphous materials, rocks, and organic matter in low-temperature geochemistry and environmental science can be found in Fenter et al (2002). 

Fendorf, S.E.. et al.. Mechanisms of chromium(III) sorption on silica. 1. Cr(I]I) surface structure derived by extended X-ray absorption fine structure spectroscopy, Environ. Sci. Technol., 28, 284, 1994. 

In the last step the U(VI) desorbs from the surface as a uranyl ion, U02 +. Two oxygen ions from the Pb02 surface remain coordinated to the high valent uranyl. Recently Combes (1989) has shown by EXAFS (extended x-ray absorption fine-structure spectroscopy) that uranyl indeed forms bidentate surface complexes on goethite. The local coordination sites on a-FeOOH are structurally very similar as the Pb02 sites with a rutile structure. 

Dahn R, Scheidegger AM, Manceau A, Schlegel ML, Baeyens B, Bradbury MH, (2001) Ni clay neoformation on montmorillonite surface. J Synchrotron Rad 8 533-535 Dahn R, Scheidegger AM, Manceau A, Schlegel ML, Baeyens B, Bradbury MH, Morales M (2002a) Neoformation of Ni phyllosilicate upon Ni uptake on montmorillonite A kinetics study by powder and polarized extended X-ray absorption fine structure spectroscopy. Geochim Cosmochim Acta 66 2335-2347... 

Figure 3 Dominant surface structure of arsenate and arsenite on goethite, showing Fe(lll)-As bond lengths determined using extended x-ray absorption fine structure spectroscopy (EXAFS).

Among the current spectroscopic methods extended x-ray absorption fine structure spectroscopy (EXAFS) has received the most attention, however other methods such as FTIR, may be equally as promising. EXAFS is considered to provide definitive information on inner- vs. outer-sphere bonding and is suitable for determining mode of attachment to the surface (monodentate, bidentate, binuclear) but does not resolve questions of surface speciation since it is not sensitive to H atoms. In addition, examination of the same system by different researchers has in some instances resulted in different conclusions. 

Surface-extended X-ray absorption fine structure (analysis) spectroscopy Sum frequency generation Second harmonic generation Surface ionization Secondary ion mass spectroscopy Subtractively normalized interfacial Fourier transform infrared spectroscopy Single potential alteration infrared (spectroscopy)... 

Technical processes that employ ionizing radiation are widely applied in the polymer field, and include the production of crosslinked wire insulation and of heat-shrink food wrappings and tubings for electrical connections, the vulcanization of rubber tires and rubber lattices, and the curing of coatings and inks. Moreover, various X-ray methods can also be appUed for the characterization and analysis of polymers, especially of the polymer surfaces. Both, X-ray imaging and X-ray microscopy allow the derivation of quantitative composition maps of polymer surfaces. Notable in this context are also near-edge X-ray absorption fine structure spectroscopy (NEXAFS), extended X-ray absorption fine structure spectroscopy (EXAFS) and X-ray photoelectron spectroscopy (XPS). 

In general, several spectroscopic techniques have been applied to the study of NO, removal. X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR), nuclear magnetic resonance (NMR), extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES) are currently used to determine the surface composition of the catalysts, with the aim to identify the cationic active sites, as well as their coordinative environment. 

---