Near-Edge X-Ray Absorption Fine Structure NEXAFS

4 Near-Edge X-Ray Absorption Fine Structure (NEXAFS) 

NEXAFS is generally characterized by spectral features near to an X-ray absorption edge and contains information about the electronic and structural properties of the adsorbing atom. This is distinct from the extended X-ray adsorption fine structure (EXAFS), which is typically observed in the region 50-1000eV above an 

The parameter used to describe the absorption of photons by a medium is the absorption coefficient a, defined according to 

The probability of exciting an electron from an initial state x r, to a final state can be described in terms of the X-ray absorption cross section, a, which is defined as the number of electrons excited per unit time divided by the number of incident photons per unit time per unit area [152]. By applying Fermi s golden rule and using the dipole approximation, can be written as 

CO Adsorption on Ni(100) As noted in Section 3.4.1.4, the polarization dependence of NEXAFS is an excellent method for determining the orientation of a small molecule on a surface. A good example of this is the adsorption of CO on Ni(lOO) [161]. The measurement is illustrated schematically on the right-hand side 

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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. 

Nd YAG Q-switched laser, in fine art examination/ conservation, 11 413 N-donating ligands, complexation with uranium, 25 434-436 Near-edge X-ray absorption fine structure (NEXAFS), 24 72... 

Lithium intercalation in VeOis has been studied by Stallworth et al. ° Variable-temperature Li NMR indicated considerable mobility for Li+ in the intercalated materials. The Li NMR data were compared with ESR spectra and near-edge X-ray absorption fine structure (NEXAFS) data on the same materials, and a correlation between vanadium oxidation state (from NEXAFS data) and NMR shift was observed. The authors explained the shifts in terms of different coupling mechanisms between the and shifts. The shifts were, however, extracted from static NMR experiments, and it is possible that some of the different local environments, typically revealed in a MAS spectrum, were not seen in this study. 

Although the occupied orbitals are of main importance, since they are directly involved in the formation of the chemical bond, the unoccupied states also provide complementary information. In X-ray absorption spectroscopy (XAS), often denoted Near Edge X-ray Absorption Fine Structure (NEXAFS), we excite a core electron to the empty states above the Fermi level [3,4,13]. There is a close connection between XES and XAS where the former gives information on the occupied orbitals while the latter relates to the character and symmetry of the unoccupied levels. Both are governed by the dipole selection rule and the localized character of the core orbitals allows a simple atom-specific projection of the electronic structure the major difference is in the final states. In XAS the empty electronic states are probed... 

Fig. 6.113. Models for (a) 6-mercaptohexadecanol and (b) 22-mercap-todecosanoic acid, adsorbed on gold substrates investigated by near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and X-ray photoelectron spectroscopy. (Reprinted from O. Dannenberger, K. Weiss, H. J. Himmel, B. Jager, M. Buck, and Ch. Woll, Thin Solid Films 307 183, copyright 1997, Fig. 6, with permission from Elsevier Science.)...

Obviously, it is important to extend the fundamental information, obtained on the single crystal model surfaces, to the more realistic powder materials. In principle, the comparison of the electronic properties of these two systems can be achieved by using the near-edge X-ray absorption fine structure (NEXAFS) technique, which can be applied to investigate the properties of both single crystals and powder materials. The catalytic properties of the model and powder carbide materials can also be compared if the relevant reactions are carried out for both systems. 

S., and Jacobsen, C. (2005). Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy for mapping nano-scale distribution of organic carbon forms in soil Application to black carbon particles. Global Biogeochem. Cycles 19, GB1013. 

This paper will discuss the use of Near-Edge X-ray Absorption Fine Structure (NEXAFS) Spectroscopy to study the unoccupied n molecular orbital (MO) structures of polymers and polymer-metal interfaces. A collection of systematic NEXAFS and EELS studies of simple organic compounds by J. Stohr and others (1-10) has led to recent advances in the understanding and interpretation of this technique. It s application to complicated polymers and polymer-metal interactions has only begun, but NEXAFS spectroscopy promises to be an important complement to other photoelectron spectroscopies. 

XPEEM is a spectromicroscopy technique utilizing near edge X-ray absorption fine structure (NEXAFS) contrast. XPEEM probes the surface chemistry by detection of photoelectrons emitted from the surface. XPEEM was performed at the PEEM2 microscope at the bending magnet beamline... 

In this article, we summarize our recent results on this topic using Near Edge X ray Absorption Fine Structures (NEXAFS) spectroscopy at the C12p edge (200 eV), with, precisely, a particular emphasis made on the description at a molecular level of the chemical state of hydrogen chloride. 

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