Synchrotron radiation spectroscopy/microscopy

Direct analysis 7.1 XRD, XRF, infrared spectroscopy (NIR and MIR), solid-state nuclear magnetic resonance (NMR), advanced spectroscopy using synchrotron radiation, neutron activation, fluorescence, and visible and electron microscopy... 

Although a number of secondary minerals have been predicted to form in weathered CCB materials, few have been positively identified by physical characterization methods. Secondary phases in CCB materials may be difficult or impossible to characterize due to their low abundance and small particle size. Conventional mineral identification methods such as X-ray diffraction (XRD) analysis fail to identify secondary phases that are less than 1-5% by weight of the CCB or are X-ray amorphous. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM), coupled with energy dispersive spectroscopy (EDS), can often identify phases not seen by XRD. Additional analytical methods used to characterize trace secondary phases include infrared (IR) spectroscopy, electron microprobe (EMP) analysis, differential thermal analysis (DTA), and various synchrotron radiation techniques (e.g., micro-XRD, X-ray absorption near-eidge spectroscopy [XANES], X-ray absorption fine-structure [XAFSJ). 

No analytical method is perfect. Spectral interpretation is still difficult, and standard spectra databases are scarce. The issues of quantification, comparison with data collected by other methods, and scale up are important, especially in spectromi-croscopy studies. Radiation damage and sectioning artifacts can make analysis of susceptible samples difficult. The biggest obstacle to widespread use of NEXAFS spectroscopy, microscopy, and spectromicroscopy in environmental studies remains the extremely limited number of such instruments. Typically, each beamline allocation committee receives 2 or 3 times as many requests for time as is available. Studies, when granted, are usually for 2-5 days every 4-6 months. Thus, scientists have to be very selective about the types of questions and samples that they choose to examine using these techniques. Continued pressure and education from the scientific community will be needed to increase the number of beamlines suitable for NOM studies in the future, even as new synchrotron facilities are planned or built. 

Ade, H., and Urquhart, S. G. (2002). NEXAFS Spectroscopy and microscopy of natural and synthetic polymers. In Chemical Applications of Synchrotron Radiation, Advanced Series in Physical Chemistry, Vol. 12, Sham, T. K., ed., World Scientific Publishing, River Edge, NJ, pp. 285-355. 

Lindau I, Spicer WE (1980) Photoemission as a tool to study solids and surfaces. In Winick H, Doniach S (eds) Synchrotron Radiation Research, Plenum Press, New York, p 159-221 Lindqvist-Reis P, Lamble K, Pattanaik S, Persson I, Sandstrocni. M (2000) Hydration of the yttrium(III) ion in aqueous solution. An X-ray diffraction and XAFS structural study. J Phys Chem 104 402-408 Lindqvist-Reis P, Munoz-Paez A, Diaz-Moreno S, Pattanaik S, Persson I, Sandstroem M (1998) The structure of the hydrated gallium(III), indium(HI), and chromium(III) ions in aqueous solution. A large angle X-ray scattering and EXAFS study. Inorg Chem 37 6675-6683 Liu C, Frenkel AI, Vairavamurthy A, Huang PM (2001) Sorption of cadmium on humic acid Mechanistic and kinetic studies with atomic force microscopy and X-ray absorption fine structure spectroscopy. Canadian J Soil Sci 81 (3, Spec. Issue) 337-348... 

For numerous questions related to the speciation of metal(loid) contaminants in natural and waste matrices, the combination of X-ray fluorescence, diffraction and absorption presented in this chapter offers a unique access to the problem. X-ray microscopy cannot compete with the atomic resolution offered by electron microscopy, but it offers a number of unique features. The chemical and structural information obtained by pSXRF and pSXRD can be used to identify the host solid phase by mapping the distributions of elements and solid species, respectively. Then the molecular-scale binding mechanism of trace elements by the host phase can be unraveled by pEXAFS spectroscopy. All these techniques can be applied with minimum preparation, minimizing any possible alteration of the sample. However, caution should be taken to not modify the initial form of the metal species by photon-assisted oxidation or reduction. This problem can be circumvented by decreasing the exposure time, photon density, or temperature. The polarization of the synchrotron radiation can be used to analyze anisotropic materials, which is important since many environmental minerals have a layered structure. 

Among the related methods, specific experimental designs for applications are emphasized. As in-system synchrotron radiation photoelectron spectroscopy (SRPES) will be applied below for chemical analysis of electrochemically conditioned surfaces, this method will be presented first, followed by high-resolution electron energy loss spectroscopy (HREELS), photoelectron emission microscopy (PEEM), and X-ray emission spectroscopy (XES). The latter three methods are rather briefly presented due to the more singular results, discussed in Sections 2.4-2.6, that have been obtained with them. Although ultraviolet photoelectron spectroscopy (UPS) is an important method to determine band bendings and surface dipoles of semiconductors, the reader is referred to a rather recent article where all basic features of the method have been elaborated for the analysis of semiconductors [150]. 

The application of AFM and other techniques has been discussed in general terms by several workers [350-353]. Other complementary techniques covered in these papers include FT-IR spectroscopy, Raman spectroscopy, NMR spectroscopy, surface analysis by spectroscopy, GC-MS, scanning tunnelling microscopy, electron crystallography, X-ray studies using synchrotron radiation, neutron scattering techniques, mixed crystal infrared spectroscopy, SIMS, and XPS. Applications of atomic force spectroscopy to the characterisation of the following polymers have been reported polythiophene [354], nitrile rubbers [355], perfluoro copolymers of cyclic polyisocyanurates of hexamethylene diisocyanate and isophorone diisocyanate [356], perfluorosulfonate [357], vinyl polymers... 

Ade H (1998) X-ray spectromicroscopy. In Samson JAR, Ederer DL (eds) Experimental methods in the physical sciences, vol 32. Academic Press, New York, pp 225-261 Ade H, Urquhart SG (2002) NEXAFS spectroscopy and microscopy of natural and synthetic polymers. In Sham TK (ed) Chemical applications of synchrotron radiation. World Scientific, Singapore, pp 285-355... 

Historically, the lack of imaging capabilities has hampered polymer characterisation by XPS. The combination of microscopy and spectroscopy has been the goal of a number of groups exploring photoelectron microscopy with X-ray or synchrotron radiation sources. The first real step towards imaging XPS (iXPS) was in 1988 (VG ESCAscope). The system allowed obtaining 2D spatial maps with a lateral resolution of < 10 /xm. The second generation of this instrument achieved a spatial resolution of approximately 2 /txm [764,769]. 

M. J. Tobin, M. A. Chesters, J. M. Chalmers, F. J. M. Rutten, S. E. Fisher, I. M. Symonds, A. Hitchcock, R. Allibone and S. Dias-Gunasekara, Infrared microscopy of epithelial cancer cells in whole tissues and in tissue culture, using synchrotron radiation, in Applications of Spectroscopy to Biomedical Problems, Faraday Disc. 126 2004, pp. 27-39. 

L. Miller, M. J. Tobin, S. Srichan, P. Dumas, About the use of synchrotron radiation in infrared microscopy for biomedical applications. In Biomedical Applications of FTIR spectroscopy, P. Harris, Editor,... 

XAS requires synchrotron radiation and a relatively large amount of material but no vacuum condition. On the other hand, EELS can be performed directly using an electron spectrometer fitted to a scanning transmission electron microscope (STEM). Here, the main advantage is the high spatial resolution attainable. (The incident electron beam can be as. small as I nm in diameter.) EELS can also be coupled with conventional transmission electron microscope (TEM) facilities and particularly high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS). 

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