X-ray absorption spectroscopy
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X-ray absorption spectroscopy (XAS) is a widely used technique for determining the local geometric and/or electronic structure of matter.[1] The experiment is usually performed at synchrotron radiation facilities, which provide intense and tunable X-ray beams. Samples can be in the gas phase, solutions, or solids.[2]
Background
XAS data is obtained by tuning the
There are three main regions found on a spectrum generated by XAS data which are then thought of as separate spectroscopic techniques (Figure 2):
- The absorption threshold determined by the transition to the lowest unoccupied states:
- the states at the arc tangent shape;line-shape (they occur in a pre-edge region at energies lower than the transitions to the lowest unoccupied level);
- the bound core excitons in insulators with a Lorentzian
- the states at the
- The X-ray absorption near-edge structure (XANES), introduced in 1980 and later in 1983 and also called NEXAFS (near-edge X-ray absorption fine structure), which are dominated by core transitions to quasi bound states (multiple scattering resonances) for photoelectrons with kinetic energy in the range from 10 to 150 eV above the chemical potential, called "shape resonances" in molecular spectra since they are due to final states of short life-time degenerate with the continuum with the Fano line-shape. In this range multi-electron excitations and many-body final states in strongly correlated systems are relevant;
- In the high kinetic energy range of the photoelectron, the scattering cross-section with neighbor atoms is weak, and the absorption spectra are dominated by XAFS.
XAS is a type of
XAS methodology can be broadly divided into four experimental categories that can give complementary results to each other:
The most obvious means of mapping heterogeneous samples beyond x‐ray absorption contrast is through elemental analysis by x‐ray fluorescence, akin to EDX methods in electron microscopy.[5]
Applications
XAS is a technique used in different scientific fields including
- Amorphous solids and liquid systems
- Solid solutions
- Doping and ion implantation materials for electronics
- Local distortions of crystal lattices
- Organometallic compounds
- Metalloproteins
- Metal clusters
- Catalysis
- Vibrational dynamics[9]
- Ions in solutions
- Speciation of elements
- Liquid waterand aqueous solutions
- Used to detect bone fracture
- Used to determine the concentration of any liquid in any tank
See also
References
- ISBN 978-1-118-67616-5, retrieved 2020-09-28
- PMID 19653117.
- PMID 29547333.
- ISBN 978-0-89118-857-5. Retrieved 2020-09-24.
- )
- ^ Tangcharoen, T., Klysubun, W., Kongmark, C., & Pecharapa, W. (2014). Synchrotron X‐ray absorption spectroscopy and magnetic characteristics studies of metal ferrites (metal= Ni, Mn, Cu) synthesized by sol–gel auto‐combustion method. Physica Status Solidi A, 211(8), 1903-1911.https://doi.org/10.1002/pssa.201330477
- ^ Tangcharoen, Thanit, Wantana Klysubun, and Chanapa Kongmark. "Synchrotron X-ray absorption spectroscopy and cation distribution studies of NiAl2O4, CuAl2O4, and ZnAl2O4 nanoparticles synthesized by sol-gel auto combustion method." Journal of Molecular Structure 1182 (2019): 219-229.https://doi.org/10.1016/j.molstruc.2019.01.049
- ^ Rawat, Pankaj Singh, R. C. Srivastava, Gagan Dixit, and K. Asokan. "Structural, functional and magnetic ordering modifications in graphene oxide and graphite by 100 MeV gold ion irradiation." Vacuum 182 (2020): 109700.https://doi.org/10.1016/j.vacuum.2020.109700
- S2CID 119210376. Retrieved 21 April 2023.
External links
- Zhang M (15 August 2020). "XANES - Theory". LibreTexts Project.
- Newville M (25 July 2008). "Fundamentals of XAFS" (PDF). Chicago, IL: University of Chicago.