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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.
Materials Characterization Using Advanced Synchrotron Radiation Techniques for Antimicrobial Materials
Published in Peerawatt Nunthavarawong, Sanjay Mavinkere Rangappa, Suchart Siengchin, Mathew Thoppil-Mathew, Antimicrobial and Antiviral Materials, 2022
Chatree Saiyasombat, Prae Cbirawatkul, Suittipong Wannapaiboon, Catleya Rojviriya, Siriwat Soontaranon, Nuntaporn Kamonsutthipaijit, Sirinart Chio-Srichan, Chanan Euaruksakul, Nichada Jearanaikoon
X-ray absorption spectroscopy (XAS) is a synchrotron-based technique for structural characterization [1-2]. The method has proven powerful as structural information obtained from crystalline or non-crystalline materials and measurements are relatively simple. Samples could be measured in solid or liquid forms, and the measurement configuration is straightforward. Absorption is determined from the absorption coefficient, μ. Following the Beer-Lambert law. I = I0e-μx (7.1) where I is the intensity of transmitted X-rays, I0 is the intensity of incoming X-rays, and x is the sample thickness. The absorption is determined from the measurement of X-ray intensity before and after samples. The schematic of a typical absorption measurement is shown in Figure 7.1(a), Also shown in Figure 7.1(b) is the illustration of the photoelectric effect describing the phenomena where an atom is exposed to X-rays with energy higher than but in the proximity of the energy level of the core electrons. Because of the photoelectric effect, the absorption coefficient is modulated. The modulation originates from the interference between outgoing and backscattered photoelectrons [2]. Local structures of the interested atoms are thus revealed by analyzing these features. Figure 7.2 shows an example of XAS spectra measured at the Fe K-edge. The spectrum is divided into two parts. The XANES (X-ray Absorption Near-Edge Structure) part gives information regarding oxidation states and the local symmetry of the atoms of interest. The EXAFS (Extended X-ray Absorption Fine Structure) part provides quantitative information of their atomic local coordination environments. Many XAS data analysis programs are available, both free and commercial, including the widely used Demeter package [3], And as XAS spectra are unique to each local environment, they can be compared to measurements of reference compounds, and fingerprinting could be used for speciation in XANES or EXAFS.
Distinctive applications of synchrotron radiation based X-ray Raman scattering spectroscopy: a minireview
Published in Instrumentation Science & Technology, 2021
XRS spectroscopy is capable of measuring changes in coordination, oxidation and spin states, local molecular structure, and electronic structure by means of low energy excitations in element of interest. The spectroscopy has been commonly used to investigate light elements K-edges,[23–25] intermediate-Z elements L-edges[26,27] and as well as M-edges,[28,29] N-edges[30,31] and O-edges[32,33] of higher-Z elements. In addition to XANES measurements, extended X-ray absorption fine structure (EXAFS) studies can be conducted through XRS to investigate the local environment around a specific atom of interest.[34,35] Unlike XAS, the technique is not restricted to transitions following the dipole selection rule. At low momentum transfer values, where the dipole allowed transitions are dominant, XRS gives the same information as XAS experiments.[10] When momentum transfer is increased, dipole forbidden excitations dominate XRS spectra.[36,37] XRS has potential to access higher order electronic excitations such as octupole and triakontadipole transitions,[38,39] controlling the momentum transfer to photoelectron both in magnitude and direction.
Investigation of temperature and pressure effects on thermodynamic parameters of intermetallic alloy in EXAFS
Published in Cogent Engineering, 2020
Extended X-ray absorption fine structure (EXAFS) spectroscopy has developed into a powerful probe of atomic structure and the high-temperature thermodynamics of substances due to anharmonicity (Iwasawa et al., 2017; Rehr, 2000). Numerous methods have been developed to investigate how temperature affects the EXAFS cumulants, such as path-integral effective-potential theory (Yokoyama, 1999), the statistical moment method (V. v. Hung et al., 2010), the ratio method (Bunker, 1983), the Debye model (Beni & Platzman, 1976), the Einstein model (Frenkel & Rehr, 1993), and the anharmonic correlated Einstein model (ACEM) (N. v. Hung & Rehr, 1997). Several groups have applied ACEM theory to EXAFS to study how the thermodynamic properties depend on temperature with the effect of the material doping ratio (DR) (Duc et al., 2017; Hung et al., 2015; Kraut & Stern, 2000; Nafi et al., 2013). However, no reports to date have discussed how the thermodynamic parameters and the Debye–Waller factor (DWF) depend on temperature and pressure for Cu, Ag, and their intermetallic alloy CuAg72. A CuAg alloy contains the elements Cu and Ag, with the Ag atoms referred to as the substitution atoms and the Cu atoms referred to as the host atoms. CuAg72 has a ratio of 72% Ag and 28% Cu (±1%) and is also known as CuSil or UNS P0772 (note: CuSil should not be confused with Cusil-ABA, which has the composition 63.0% Ag, 35.25% Cu, and 1.75% Ti). It is an eutectic alloy and is used primarily for vacuum brazing (Nafi et al., 2013).