Near-edge fine structure

X-ray absorption spectroscopy combining x-ray absorption near edge fine structure (XANES) and extended x-ray absorption fine structure (EXAFS) was used to extensively characterize Pt on Cabosll catalysts. XANES Is the result of electron transitions to bound states of the absorbing atom and thereby maps the symmetry - selected empty manifold of electron states. It Is sensitive to the electronic configuration of the absorbing atom. When the photoelectron has sufficient kinetic energy to be ejected from the atom It can be backscattered by neighboring atoms. The quantum Interference of the Initial... 

EELS spectra showing the distinction between copper atom environments on the basis of the near edge fine structure of the CuL edge,... 

In solid state physics, the sensitivity of the EELS spectrum to the density of unoccupied states, reflected in the near-edge fine structure, makes it possible to study bonding, local coordination and local electronic properties of materials. One recent trend in ATEM is to compare ELNES data quantitatively with the results of band structure calculations. Furthermore, the ELNES data can directly be compared to X-ray absorption near edge structures (XANES) or to data obtained with other spectroscopic techniques. However, TEM offers by far the highest spatial resolution in the study of the densities of states (DOS). 

Fig. 7. Variations in the near-edge fine structure at the Pt Lm edge of a Pt/zeolite catalyst during CO oxidation exhibiting chemical oscillations [adapted from Hagelstein et at. (45)).

Synchrotron-based N K-edge X-ray absorption near-edge fine structure (XANES)... 

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. 

Extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge fine structure (XANES) have been used with great success to characterize highly dispersed supported metals. EXAFS can provide information on the local structure of highly dispersed metal on a support, such as alumina, and XANES, measured at the same time, provides information on the valence state of the metal. 

A few structures have been solved by x-ray adsorption near-edge fine structure (XANES), including oxygen on Ni(100)./16/ This technique is also known as near-edge x-ray adsorption fine structure (NEXAFS). 

Figure 7.26. Electron energy-loss spectroscopy (EELS) spectra. Shown (top) is a representative EELS spectrum of a nickel oxide sample. A typical EELS spectrum shows a zero-loss peak that represents the unscattered or elastically scattered electrons, the near-edge fine structure (ELNES), and extended energy-loss fine structure (EXELFS). Also shown (bottom) are the fingerprint regions of an EELS spectrum, just beyond the core-electron edges, which provide information regarding the detailed bonding and chemical environment of the desired element.

Garvie E. A. J., Craven A. J., and Brydson R. (1994) Use of electron energy-loss near-edge fine structure in the study of minerals. Am. Mineral. 79, 411-425. 

Fig. 3 Combining atomically resolved STEM EELS with modelling can reveal the bonding environment of individual atoms. DFT modelling of EELS near-edge fine structure shows that 3-fold coordinated Si impurities in graphene adopt a distorted, out of plane, geometry, while the bonding of 4-fold coordinated Si impurities is in-plane. Figure reprinted with permission from Q. M. Ramasse eta/.. Nano Lett., 2012, 13, 4989-4995. Copyright 2012 American Chemical Society.

Diffusion profiles across interfaces can also be extracted from EELS data provided that the effects of the probe size and shape are properly taken into account. An interesting comparison of the near-edge fine structure in EELS spectra from four Si-containing materials is shown in Figure 4. The differences in the shapes of these spectra, which can be replicated theoretically, are due to differences in composition as well as changes in the local chemical bonding (i.e., the local atomic environment). 

Phase Separation Using the Near-Edge Fine Structure... 

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