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Methods of Investigating Structure and Chemical Composition
Published in Rishat G. Valeev, Alexander V. Vakhrushev, Aleksey Yu. Fedotov, Dmitrii I. Petukhov, A. N. Beltiukov, A. L. Trigub, A. V. Severyukhin, Nanostructured Semiconductors in Porous Alumina Matrices, 2019
Rishat G. Valeev, Alexander V. Vakhrushev, Aleksey Yu. Fedotov, Dmitrii I. Petukhov
Copper is introduced into zinc sulfide as the main electroluminescence activator. Copper can react with sulfur and form the inclusions of CuxS phase. At the same time, a lot of heterojunctions of ZnS/CuxS, on which the generation and radiative recombination of charge carriers take place during the electric field excitation, are formed in the phosphor volume. X-ray structural analysis allows detecting and attesting the structure of copper sulfide inclusions. Copper can form point defects of penetration, being the luminescence centers. The emission color depends on penetration type of copper and coactivators. Associates (copper in zinc node)–(copper in interstice) produce the emission of blue color, associates (copper in zinc node)–(chlorine in sulfur node)—the emission of green color.11 Thus, depending on the copper concentration, the predominance of one or another electroluminescence mechanism is possible. Furthermore, it becomes problematic to determine the position of copper atom in the zinc sulfide lattice and its chemical state by the method of X-ray structural state. In this case, it is possible to apply X-ray absorption fine structure (XAFS) methods for investigating the local atomic structure.
Detector Characterization
Published in Alan Owens, Semiconductor Radiation Detectors, 2019
X-ray Absorption Fine Structure measurements (XAFS) are routinely carried out at synchrotron facilities to probe both short- and long-range order in materials. XAFS is a generic term and can be broken down into structure originating far from an absorption edge and structure originating close to the edge, which arise from different processes. Extended X-ray Absorption Fine Structure (EXAFS) is a diagnostic of short-range order by means of which details in the local geometry (atom types, bond lengths and bond angles) around the photo-absorbing atom can be extracted from far-edge spectra. X-ray Absorption Near Edge Structure (XANES), on the other hand, is a diagnostic of long-range order through which details of atom types and how they are structured collectively (the coordination environment) can be extracted from near-edge spectra. XAFS measurements, both EXAFS and XANES, can also be applied to detector metrology. For example, several authors have noted the wide spread in the radiation detection properties of Cd1-xZnxTe crystals and have attempted to use the structural information embedded in XAFS to find a link between performance and structural perfection.
Established and Emerging Techniques for Characterising the Formation, Structure and Performance of Calcified Structures under Ocean Acidification
Published in S.J. Hawkins, A.L. Allcock, A.E. Bates, L.B. Firth, I.P. Smith, S.E. Swearer, P.A. Todd, Oceanography and Marine Biology, 2019
Susan C. Fitzer, Vera Bin San Chan, Yuan Meng, Kanmani Chandra Rajan, Michio Suzuki, Christelle Not, Takashi Toyofuku, Laura Falkenberg, Maria Byrne, Ben P. Harvey, Pierre de Wit, Maggie Cusack, K. S. Gao, Paul Taylor, Sam Dupont, Jason M. Hall-Spencer, V. Thiyagarajan
An alternative emerging technique for determining the mineral composition of marine skeletons is high-spatial resolution synchrotron X-ray photo emission electron microscopy (XPEEM) combined with X-ray absorption spectroscopy (XAS) (Fitzer et al. 2016). The benefits of the XPEEM and XAS over SEM is the high level of spatial resolution, as well as the fact that it can detect without the need for an energy filter by measuring the secondary electrons yield as a function of photon energy. This technique can be applied alongside EBSD to identify mineral phases throughout the shell structure (Fitzer et al. 2016). X-ray absorption near edge structure (XANES) and XPEEM techniques use the principles of X-ray absorption fine structure (XAFS), which interpret the scattering of photoelectrons emitted from an absorbing atom in a structure when excited by high-energy photons (Politi et al. 2008, Fitzer et al. 2016). XANES has been used as a tool to examine the phase transformation mechanisms of amorphous CaCO3 into calcite, particularly in sea urchin larval spicules (Politi et al. 2006, 2008, Gong et al. 2012). Recently, XPEEM combined with XAS has been used as a tool to examine amorphous CaCO3 in mussels reared under OA conditions (Fitzer et al. 2016) showing more induced amorphous CaCO3 with less crystallographic control over shell formation. This technique was applied to address the question of OA impact on biomineralisation and shell repair to determine the protective function of the shell under changing environments (Fitzer et al. 2016). The technique requires the embedding and fine-polishing of samples, similar to SEM-EBSD preparation (Politi et al. 2008, Perez-Huerta & Cusack 2009, Fitzer et al. 2016). XANES and XPEEM have the advantage of providing high spatial resolution to locate amorphous CaCO3 embedded within the shell structure when applied in combination with SEM techniques (Politi et al. 2008). Disadvantages include the high instrumentation cost and lengthy sample preparation time.
Remediation of Clay Soils Contaminated with Potentially Toxic Elements: The Santo Amaro Lead Smelter, Brazil, Case
Published in Soil and Sediment Contamination: An International Journal, 2018
L. R. P. de Andrade Lima, L. A. Bernardez, M. G. dos Santos, R. C. Souza
The X-ray absorption spectroscopy (XAS) includes the X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions. In the present case, soil samples were used to perform EXAFS at the Brazilian Synchrotron Light Laboratory (LNLS) on the XAFS2 beam line. The energy calibration was done using a Pb foil and the transmission was measured at the Pb-LIII edge (Manceau et al., 1996). The measurements were replicated two or three times. Seven pure Pb compounds were used as standards: Pb, PbS, PbSO4, PbCO3, PbO, PbO2, and Pb2O3. Samples of the contaminated soil were used to evaluate the Pb pollutants, and soil samples were used to perform a dynamic EXAFS. A tubular furnace with a controlled atmosphere, using injection of synthetic air or argon, was used. The X-ray absorption spectra were repeatedly collected after temperature stabilization at 25, 400, 600, 800, 900, and 1000 °C. The EXAFS data analysis was performed using the Athena XAS data processing program v.0.9.22 (Ravel and Newville, 2005). The pre-edge background was removed and the post edge continuum was modeled using fit procedures. The normalized EXAFS data (c) were converted into wave vector (k) and k2 weighted data (Ravel and Newville, 2005).
X-ray absorption study of oxide film formed on Alloy 600 in PWR primary water at 290°C with a decreased concentration of dissolved hydrogen
Published in Journal of Nuclear Science and Technology, 2023
Kenta Kakitani, Takaaki Kobayashi, Hiroaki Abe
To accomplish the above objectives, the valence state of Fe and local structure of the oxide film on Alloy 600 were analyzed by X-ray absorption fine structure (XAFS) measurements at the Fe K-edge. XAFS measurements provide a direct means to explore material properties; the valence state of a specific element can be resolved from the X-ray absorption near-edge structure (XANES) region, while the structural information such as bond length can be derived from the extended X-ray absorption fine structure (EXAFS) region [15].