Fine structure techniques

The Cu adsorbate structure was studied using STM and EXAFS (extended x-ray absorption fine structure) techniques, but it is not yet well understood. UPD-OPD transition is in the range —82 to —71 mV. Bulk fee Cu spacing is reached after deposition of about lOCu monolayers. Holzle et al. (72) have shown that UPD Cu deposition on Au(l 11) is a combined adsorption-nucleation and growth process. 

The Cu adsorbate structure was studied using STM and EXAFS (extended X-ray absorption fine structure) techniques, but it is not yet well understood. 

Extended X-ray Absorption Fine Structure) technique, concerning nanocrystalline materials, is reviewed. The potentialities of the technique to characterise hulk materials, thin films, and structural evolution during the preparation of nanoparticles using in situ set-ups are presented. 

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... 

A fine - structure technique (see EXAFS). Core holes are excited by monoenergetic electrons. The modulation in the excitation cross section as the beam energy is varied may be monitored through absorption, fluorescence, or Auger emission. 

Monoenergetic photons excite a core hole. The modulation of the absorption cross section with energy at 100 - 500 eV above the excitation threshold yields information on the radial distances to the neighbouring atoms. The cross section can be measured by fluorescence as the core holes decay or by attenuation of the transmitted photon beam. EXAFS is one of the many fine -structure techniques. 

A core hole is excited as in fine - structure techniques (see EXAFS, SEXAFS, ARPEFS, NPD, APD, EXELFS, SEELFS)... 

A fine - structure technique similar to EXELFS, except the incident electron is more surface - sensitive because of the lower excitation energy. 

EXELFS Extended X-ray Energy Loss Fine Structure A fine-structure technique similar to EXAFS, except that 60-300 KeV electrons rather than photons excite core-holes. Like EXAFS, this techniques is not explicitly surface sensitive. 

There are a large number of fine structure techniques, all based on the same physical principle. In all of these techniques an electron is ejected from an atomic core-level by incident photons or other particles. The different names refer to different experimental arrangements for the excitation and detection of core-holes. 

If there are different local geometries for source atoms, the different fine structures will be superimposed in the experimental spectrum, which will then be more difficult to interpret. Fine structure techniques are particularly useful when a chemisorbed atom is used as the source atom. 

Almost all of the existing quantitative data on surface structure was obtained through experimental techniques that involve the propagation and scattering of electrons in solids. This class of surface probes includes the whole range of fine-structure techniques, in addition to LEED and angle-resolved photoemission experiments. This chapter will provide a theoretical description of these techniques and the methods of analyzing the experimental data to determine surface structure. 

In the angle integrated mode, electrons emitted in many different directions are accumulated simultaneously. To an appreciable extent this averages out the structure-dependent effects of step 4, and therefore emphasizes the information arising from the primary and secondary events of steps 2 and 3, such as the radial distances determined in fine-structure techniques like SEXAFS. 

We next turn to the high-energy fine-structure techniques ... 

With the other fine-structure techniques (EXAFS, SEXAFS, EAPFS, etc.), the above mentioned approximations lead to the following general relationship for the intensity modulation at the detector /41,42,43/... 

By using non-invasive techniques, it is possible to determine the concentration and oxidation state of vanadium in living cells. In A. ceratodes, EXAFS (X-ray absorption fine structure) techniques showed that 90% of the vanadium is in the form of V(III), 10% is V(IV)84. In A. nigra, EPR (electron paramagnetic resonance) spectroscopy showed that 95% of the vanadium is in the V(III) form, and 5% is V(IV)85. ... 

Electron appearance EAPFS A fine-structure technique (see EXAFS). Core holes are excited by Atomic structure... 

Lytle, F. W., Sayers, D. E., and Stern, E. A. Extended X-ray-absorption fine-structure technique. II. Experimental practice and selected results. Phys. Rev., Bll, 4825-4835 (1975). 

X-ray scattering and extended X-ray absorption fine-structure techniques. Data indicate that the indium ion is coordinated by six water molecules, and the In—O bond distance in the first hydration sphere is 2.131(7) A. Changes in concentration or the anion had no influence on this... 

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