Synchrotron-based characterization

Advanced synchrotron based characterization techniques of solid state applied to macromolecules are reported in Chapter 4. After an introduction to the physics and principles of NEXAFS and XPS spectroscopy, the main features of these techniques that allow a non conventional assessment of the electronic and chemical structure are depicted. The study of macromolecular organization and self-assembly can be nicely obtained by these spectroscopic tools. For example the formation of SAMs (Self Assembled Monolayers) of a variety of molecules arranged in supramolecular assemblies can be detected as well as the behaviour of biomolecules bound to surfaces mimicking biological substrates. Many examples of macromolecules studied with NEXAFS and XPS highlight the potential of these spectroscopic methods to give insight into the molecular and supramolecular structure which in turn determine the most desired properties. 

MCB MCC MINEQL MOX MSWI p,-SXRF MW Microwave burn-out Materials Characterization Center Mineral equilibria (computer program) Mixed-oxide (fuel) Municipal solid waste incinerator Synchrotron-based X-ray microfluorescence Magnox waste glass (British Nuclear Fuel Public Ltd. Company)... 

Techniques of microscopic XRF ( j,-XRF) developed in the last 20 years provide 2D images and elemental maps of each element present in the target material. Portable/in situ p-XRF, j,-XRF spectrometers synchrotron-based ( -SRXRF) and micro-x-ray absorption spectroscopy/micro-x-ray absorption near-edge structure spectroscopy (XAS/ J,-XANES) have improved the mineralogical characterization, as well as the elemental and chemical imaging of samples at the submicrometer scale [61]. 

The table is organized as follows Column 2 lists methods used to complement the XRD experiments. It is obvious from the analysis of the literature that most investigations have required (within the same report) the availability of complementary data for the interpretation of the XRD results. By far the most common complementary techniques are EXAFS and XAS to characterize the evolution of short- and long-range ordering simultaneously. The pairing of this very important basic information about the constitution of a catalyst has even led to the construction of a combined synchrotron-based experiment whereby both techniques were used with catalysts in complex reaction atmospheres (Clausen et al., 1993 Dent et al., 1995 Grunwaldt and Clausen, 2002 Sankar et al., 2000). 

To date, standard bulk XAFS has been the most widely used synchrotron-based technique used to characterize heavy metals in environmental samples. However, in soils and sediments, microenvironments exist that have isolated phases in higher concentrations relative to the average of the total matrix.53 For example, the microenvironment of oxides, minerals, and microorganisms in the rhizosphere has been shown to have a quite different chemical environment compared to the bulk soil.60 Often these phases may be very reactive and of significance in the partitioning of... 

Figure 2 shows synchrotron based X-ray fluorescence micro-analyses, which reveal the distribution of sulphated polysaccharides within the Goniastrea walls and septa (Fig. 2a). The EMZ regions are characterized by high concentrations of...

NEXAFS is a synchrotron-based spectroscopic tool routinely used as a complementary technique with XPS for surface characterizations. This method probes the adsorption of X-rays by the excitation of core (K-shell) electrons into unoccupied electronic states near the ionization limit. Subsequent emission of Auger electrons results in the formation of an NEXAFS electron yield the observed spectmm. Because the source of Auger electrons can extend only up to 10 nm and the spectral peak positions and intensities are directly related to the nature of unoccupied electronic states, NEXAFS spectroscopy provides an important tool for studying stmctural and chemical features of various surface thin films and coatings (Hemraj-Benny et al., 2006 Hahner, 2006). 

In the past years advanced characterization techniques such as synchrotron-based X-ray tomography have allowed to accurately determine the structure of the GDL materials including the effects of compression in the cell [4]. In combination with electrochemical methods [5, 6], this has lead to accurate determination of the effective diffusion coefficients as defined in Eq. 2. in dry GDL, depending on the compression and the direction (in- or through-plane), is in the range between 0.6 and 0.2 times the diffusion coefficient in the free volume (see Fig. 3). 

This chapter will highlight Li-ion battery research using 2D and 3D synchrotron based X-ray imaging techniques and show examples from characterizations of full electrodes as well as single particles. We will give a brief introduction into the available techniques and designated set-ups to make room for the results that... 

XRD is an excellenr, nondestructive method for identifying phases and characterizing the structural properties of thin films and multilayers. It is inexpensive and easy to implement. The future will see more use of GIXD and depth dependent measurements, since these provide important information and can be carried out on lab-based equipment (rather than requiring synchrotron radiation). Position sensitive detectors will continue to replace counters and photographic film. 

Chouparova, E. Lanzirotti, A. Feng, H., et al., Characterization of Petroleum Deposits by Synchrotron Radiation-Based Microanalyses. Energy Fuels, 2004. 18 pp. 1199-1212. 

Up to 1999, only metal atoms [1-5], metal clusters [6,7], metal nitrides [55-57], and noble gas atoms [58-60] were observed to be encaged inside C60, C70, or various sizes of higher fullerenes. The experimental evidence for carbon atoms or metal-carbon compounds (carbides) being encapsulated inside fullerenes had not yet been observed. In 2000, Shinohara et al. succeeded in the first production, isolation, and spectroscopic characterization of a scandium carbide endohedral fullerene (Sc2C2) C84. Following this, the first experimental evidence based on synchrotron X-ray diffraction was presented and revealed that the Sc carbide is encapsulated in the form of a lozenge-shaped Sc2C2 cluster inside the D2d-C84 fullerene [8]. 

In spite of numerous studies on Nd-carboxylate-based catalyst systems a mechanistic understanding of the formation and the chemical structure of the active species is far off. By the application of new analytical methods some progress has recently been achieved. Kwag and co-workers applied synchrotron X-ray absorption in combination with UV-VIS-spectroscopy. These authors succeeded to characterize the reaction product obtained by the pre-formation of the catalyst components NdV HV9/TIBA/DEAC. The following essential features are reported about the reaction product (1) Nd-C bonds (bond length = 1.41 A) with covalent and ionic character, (2) Nd- Cl bonds... 

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