Extended X-ray absorption spectroscopy EXAFS

EXAFS Extended X-ray absorption spectroscopy FT Fourier transform... 

Linear absorption measurements can therefore give the first indication of possible alloy formation. Nevertheless, in systems containing transition metals (Pd-Ag, Co-Ni,. ..) such a simple technique is no longer effective as interband transitions completely mask the SPR peak, resulting in a structurless absorption, which hinders any unambiguous identification of the alloy. In such cases, one has to rely on structural techniques like TEM (selected-area electron diffraction, SAED and energy-dispersive X-ray spectroscopy, EDS) or EXAFS (extended X-ray absorption fine structure) to establish alloy formation. 

Thus, it becomes possible to obtain supported Rh catalysts containing very small Rh particles. In samples of Rh(T0A)/y-Al203 (1% (w/w)) the Rh particle sizes are around 1.1 nm, as indicated by HRTEM analysis (Figure 8). EXAFS (Extended X-ray Absorption Fine Spectroscopy) studies performed on the same samples give 0.7-1.0 nm as a better estimate of the value [24]. It is noteworthy that the... 

Single-crystal X-ray determination, elemental analysis, and mass-spectroscopy are used for the characterisation of complexes and products. Cyclic voltammetry, EXAFS (Extended X-ray Absorption Fine Structure Spectroscopy), NMR, UV-vis spectroscopy, and IR can also be used to determine electronic properties of the ligands and their complexes [7],... 

Figure 1.1 The electiomagnetic spectrum, showing the different microscopic excitation sources and the spectroscopies related to the different spectral regions. XRF, X-Ray Fluorescence AEFS, Absorption Edge Fine Structure EXAFS, Extended X-ray Absorption Fine Structure NMR, Nuclear Magnetic Resonance EPR, Electron Paramagnetic Resonance. The shaded region indicates the optical range.

Table 5.2 Summary of selected analytical methods for molecular environmental geochemistry. AAS Atomic absorption spectroscopy AFM Atomic force microscopy (also known as SFM) CT Computerized tomography EDS Energy dispersive spectrometry. EELS Electron energy loss spectroscopy EM Electron microscopy EPR Electron paramagnetic resonance (also known as ESR) ESR Electron spin resonance (also known as EPR) EXAFS Extended X-ray absorption fine structure FUR Fourier transform infrared FIR-TEM Fligh-resolution transmission electron microscopy ICP-AES Inductively-coupled plasma atomic emission spectrometry ICP-MS Inductively-coupled plasma mass spectrometry. Reproduced by permission of American Geophysical Union. O Day PA (1999) Molecular environmental geochemistry. Rev Geophysics 37 249-274. Copyright 1999 American Geophysical Union...

EXAFS (Extended X-Ray Absorption Fine Structure). Characterization of the surface of metal nanoparticles had been limited to chemical methods, e.g., chemisorption of hydrogen and carbon monoxide. In 1970s, the situation was surprisingly changed due to the advances in x-ray absorption spectroscopy, especially extended x-ray absorption fine structure (EXAFS), Advances in this method have been achieved with the use of synchrotron radiation, which runs effectively at Tsukuba (Japan), Grenoble (France), etc. Now it is one of the most valuable tools to get structural information on bimetallic nanoparticles. 

A non exhaustive description of the history of X-ray Absorption Spectroscopy (XAS) can be found in Ref. 1. The modem EXAFS (Extended X-ray Absorption Fine Structure) technique began in the early seventies of the last century. It corresponds to the concomitance of both theoretical and experimental developments. Between 1969 and 1975, Stem, Sayers and Lytle succeeded in interpreting theoretically the X-ray Absorption Structures observed above an absorption edge [2], while during the same period, the advent of synchrotron radiation (SR) sources reduced drastically the acquisition time of a spectrum if compared to data obtained with conventional X-ray tubes. XAS provides essential information about the local atomic geometry and the electronic and chemical state of a specific atom, for almost any element of the periodic table (Z>5). This prime tool for... 

Technique abbreviations AES = Auger Electron Spectroscopy EXAFS = Extended X-Ray Absorption Fine Structure ISS = Ion Scattering Spectroscopy SIMS = Secondary Ion Mass Spectroscopy UPS = Ultraviolet Photoelectron Spectroscopy XANES = X-Ray Absorption Near Edge Structure XPS (or ESCA) = X-Ray Photoelectron Spectroscopy bAnalysis type C = chemical, E = elemental... 

Acronyms abound in photoelectron and related spectroscopies but we shall use only XPS, UPS and, in Sections 8.2 and 8.3, AES (Auger electron spectroscopy), XRF (X-ray fluorescence) and EXAFS (extended X-ray absorption fine structure). In addition, ESCA is worth mentioning, briefly. It stands for electron spectroscopy for chemical analysis in which electron spectroscopy refers to the various branches of spectroscopy which involve the ejection of an electron from an atom or molecule. However, because ESCA was an acronym introduced by workers in the field of XPS it is most often used to refer to XPS rather than to electron spectroscopy in general. 

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. 

EXAFS — Extended X-ray absorption fine structure spectroscopy. X-ray spectroscopy close and slightly above the X-ray absorption edge. See surface analytical methods. 

P. aer. = Pseudomonas aeruginosa A. den. = Alcaligenes denitrificans MCD = magnetic circular dichroism EPR = electron paramagnetic resonance XAS = X-ray absorption spectroscopy NMR = nuclear magnetic resonance EXAFS = extended X-ray absorption fine structure. 

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