EXAFS
Extended X-ray Absorption Fine Structure · Also known as: EXAFS spectroscopy, X-ray absorption spectroscopy
Extended X-ray Absorption Fine Structure (EXAFS) is a synchrotron-based X-ray spectroscopy technique that measures the local geometric and electronic structure around a specific atom in any material, crystal or amorphous. Discovered by Sayers, Stern, and Lytle in 1971, EXAFS reveals interatomic distances, coordination numbers, and disorder in the atomic environment by analyzing oscillations in the X-ray absorption spectrum above an absorption edge.
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When to use it
Apply EXAFS to determine local atomic structure in materials where long-range crystallinity is absent or unimportant: amorphous catalysts, glasses, disordered alloys, and metal sites in proteins and enzymes. EXAFS is element-selective and probes the first and second coordination spheres. Requires access to a synchrotron beamline.
Strengths & limitations
- Element-specific: selects one atom type, avoiding interference from other elements
- No crystallinity required: works equally well for crystals, glasses, and amorphous materials
- Coordination geometry revealed: distances and coordination numbers extracted from a single scan
- Local structure information: probes 1-3 Ångströms around the absorbing atom
- Requires synchrotron radiation; beamline access is limited and expensive
- Low-Z elements (< Ca): EXAFS signals weaker; technique less sensitive for light atoms
- Interpretation ambiguous when similar atoms occupy nearby sites
- Multiple scattering at high energies complicates analysis for heavy atoms and extended distances
Frequently asked
What is the difference between EXAFS and XANES?
XANES (X-ray Absorption Near Edge Structure) probes the region within ~50 eV of the absorption edge and reveals oxidation state and local symmetry. EXAFS probes 50-1000 eV above the edge and reveals atomic distances and coordination numbers. XANES has lower spatial resolution but is faster to measure.
How does EXAFS determine coordination number?
The amplitude of oscillations in EXAFS is proportional to the number of scattering atoms at a given distance. Fitting theoretical models to the data yields the coordination number (number of neighbors) at each distance shell.
Can EXAFS distinguish between different atoms at the same distance?
Not perfectly, but elements with different atomic numbers scatter X-rays with different strengths and phase shifts. With careful analysis and comparison to reference compounds, one can partially distinguish neighboring atom types. X-ray diffraction provides definitive element identification.
Sources
- Sayers, D. E., Stern, E. A., & Lytle, F. W. (1971). New technique for investigating noncrystalline structures: Fourier analysis of the extended X-ray absorption fine structure. Physical Review Letters, 27(18), 1204-1207. DOI: 10.1103/PhysRevLett.27.1204 ↗
- Stern, E. A., Sayers, D. E., & Lytle, F. W. (1975). Extended x-ray-absorption-fine-structure technique. Physical Review B, 11(12), 4836-4846. DOI: 10.1103/PhysRevB.11.4836 ↗
How to cite this page
ScholarGate. (2026, June 3). Extended X-ray Absorption Fine Structure. ScholarGate. https://scholargate.app/en/spectroscopy/exafs
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