Near-Edge X-Ray

The shape of the edge itself examined by XANES (X-ray near-edge spectroscopy) can be employed to reveal information on d-band vacancy concentration vs. treatment. The oscillations at energies above the edge (EXAFS) ctui provide information on near-neighbor atom spacing tuid some limited information on the chemical environment. As we will show, the best way to use such tools is to use several at once, rather them only one. 

Surface analytical techniques such as Auger electron spectroscopy (27), X-ray photoelectron spectroscopy (28), and secondary-ion mass spectrometry (29) have been used to study LB films. Synchrotron radiation is a particularly powerful probe enabling X-ray near-edge structure and extended X-ray absorption fine structure to be measured. Angle-resolved photoemission studies (30) confirmed the existence of a one-dimensional energy band along the (CH2)jc chain in a fatty acid salt film. 

In many materials problems, for example at surfaces or interfaces, the chemical composition and nuclear coordinates are not fully known. Indeed, any information which can be obtained by theory on these basic structural properties will be useful, in conjunction with experiment. Spatially Resolved Electron Energy Loss Spectroscopy (SREELS), X-ray near-edge absorption (XANES) and emission, Mossbauer spectra, etc. provide site-specific probes which can be combined with theory to help resolve structures. 

Some recent investigations have applied advanced spectroscopic methods to nondestructively probe the associations between Fe oxides and other metals in Fe plaque with unprecedented spatial resolution. These techniques include x-ray fluorescence microscopy (XRF) and x-ray near-edge spectroscopy (XANES). Hansel et al. (2001) investigated the sequestration of Pb, Mn, and Zn to Fe plaque on the wetland plant Phalaris arundinacea (reed canarygrass) from a mine waste-contaminated site. They found that Pb was concentrated within the Fe plaque. However, extended x-ray absorption fine structure (EXAFS) data indicated that the Pb was not directly coordinated with the Fe oxides but was probably bound to organic matter in the form of a biofilm. Mn and Zn were also associated with Fe plaque, but chemically they appeared to exist as discrete carbonates. This work on Pb contrasts somewhat with that of Ye et al. (1998), who reported that Pb was not bound significantly to Fe plaque in Typha. 

XANES or X-ray Near Edge Structure is the fine structure very close to an X-ray absorption edge that is mainly dominated by multiple scattering effects. Also called NEXAFS for Near Edge X-ray Absorption Fine Structure. 

The Edge Region. - The X-ray near edge structure, or XANES, may be considered as a combination of two contributions. 

Interpreting the Friedel effect/law of inducing of an inversion center in a crystal (unit cell) structure by optical perturbation, in special due to the X-ray near-edge of absorption of characteristic spectra Connecting the physical perturbation of crystal S5mimetry with Curie principle that provides a practical receipt characterizing the system + perturbation common symmetry by considering their commonalities ... 

Transpassive dissolution of Cr and sputter deposited Cr oxides studied by in situ X-ray near edge spectroscopy. J Electrochem Soc 143 3997 005. doi 10.1149/l.1837327... 

In the purple film, both inclination of EDT-TTF(SCig)2 and disorder in the alkyl chains occurred. The value of the inclination angle of the TTF part was determined to be 24° by IR analysis. Isolated triiodide ions changed to chains, which was confirmed by resonance Raman spectra. The polyiodide anions exist parallel to the substrate from the X-ray near-edge structure, which was consistent with the short interlayer periodicity. 

Waychunas, G. A., Apted, M. J. Brown Jr, G. E. (1983) X-ray K-edge absorption spectra of Fe minerals and model compounds I. Near-edge structure. Phys. 

Figure 1 The L3 X-ray absorption spectrum of a Pt foil. Region I the pre-edge, II the X-ray absorption edge and near-edge structure (XANES) and III the extended X-ray...

The absorption edges in Fig. 10.10 are not perfectly sharp, but have a delicate fine structure ("Kossel35 lines") that was first explored in the 1930s. Since about 1970, this fine structure is now used in EXAFS (extended X-ray absorption edge fine structure spectroscopy) and in XANES (X-ray absorption near edge spectroscopy) the oscillations are due, again, to a chemical shift, which can be used to identify the local chemical environment of the emitting element in the sample. 

As the region near an X-ray absorption edge is scanned in energy, the ejected photoelectron sequentially probes the empty electronic levels of the material. Theoretically, interest in core-state excitation has developed considerably since the work of Mahan (179) and Nozieres and De Dominicis (219) on the singular response of the conduction electrons (in metals) to the sudden potential created by removal of a core electron. The resulting electron-hole pair excitations lead to a threshold edge asymmetry. 

XAFS - X-ray absorption edge spectroscopy XANFS - X-ray absorption near edge structure XAS - X-ray absorption spectroscopy Xg - a high-energy intermediate... 

The tunability of synchrotron radiation allows for data collection at or near the x-ray absorption edge of anomalous scatterers present in the protein or crystal to provide experimental phase information. Using techniques such as multi-wavelength anomalous dispersion (MAD) and single-wavelength anomalous diffraction (SAD) researchers are now able to solve macromolecular structures in a matter of days or weeks, a process that required months, or even years, a decade ago. 

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