2. AR
Acronym
• XAFS X-ray Absorption Fine Structure or XAS X-ray Absorption
Spectroscopy
• XANES X-ray Absorption Near Edge Structure or NEXAFS Near Edge X-ray
Absorption Fine Structure
• EXAFS Extended X-ray Absorption Fine Structure
XANES
Local Symmetry
Oxidation state
EXAFS
Bond distance
Neighbor's nature
XAFS/XAS
3. AR
Basic Principles
• X-ray Absorption Spectroscopy (XAS)
• Interaction of inner electron with the X-ray (involvement of the Core
electron)
• Incident x-ray energy should be higher than the binding energy of the core
e-
K-edge
L-edge
M-edge
Incoming
X-ray
e-
Vacuum level
1
2
3
4
Auger e-
1
2
3
4
Excitation of core e- by
incoming x-rays
Promotion of core e- to
vacuum level
e- transfer from higher to
lower level
Energy released in terms of
auger e-/ fluorescent x-ray
‘Photoelectric effect’
4. AR
Basic Principles
• Relaxation process: After excitation, the relaxation process can be done by
the demotion of electron from higher level to ground state.
X-ray Fluorescence and Auger effect
https://doi.org/10.1007/978-0-387-92897-5_1224https://jascoinc.com/learning-center/theory/fluorescence-spectroscopy/
6. AR
Basic Principles
Energy range
XANES EXAFS
5-150 eV Beyond 150 eV
Kinetic energy of the photo electron,
For XANES, low energy and higher wavelength is responsible for multiple scattering
For EXAFS corresponding to single scattering
1st shell1st shell
2nd shell
single scatteringMultiple scattering
7. AR
• Absorption edge Energy at which sharp rise of the absorption coefficient
due to generation of photoelectron by the atom
• Threshold energy defend as the energy beyond which
continuous production of photoelectron happens
• At Absorption edge, energy of incident X-ray equal to
binding energy of the core level electron.
Basic Principles
Pre-edge linked to crystal field transition from core level to empty
higher level. The weak intensity because ∆l = 2,
• features of Transition metal in Periodic Table,
• sensitive to the metal coordination number and symmetry
XANES contains Pre-egde, Absorption edge, White line
Introduction to X-ray Absorption Spectroscopy by Bruce Ravel, Synchrotron Science Group National Institute of Standards and Technology & Beamline
for Materials Measurements National Synchrotron Light Source II, September 30, 2015
White line is the main feature in the main rise of the absorption
and mostly the highest peak. It is related to transitions of the photo
electron into the molecular orbital
8. AR
Monochromatic
ray
Ionization chamber Ionization chamber
DetectorI0 It
Fluorescent
Detector
Transmission
mode
Fluorescent
mode
Lambert-Beer law
If
Absorption coefficient: μ
I0 = Ite-μt where, t is the thickness of the sample
μ depends on X-ray energy E and atomic number z by the following equation:
μ = (ρz4)/(AE3) A atomic mass and ρ density
Instrumentation
9. AR
Fundamentals of XAFS by Matthew Newville Consortium for Advanced Radiation Sources University of Chicago, Chicago, IL
Absorption Coefficient
10. AR
Major synchrotron sources all over the world
X-ray Absorption Spectroscopy by J. E. PENNER-HAHN The University of Michigan, Ann Arbor, MI, USA
11. AR
Application
• Surface study- Thin film
• Catalysis study
• Material Science- Superconductor, Energy storage
• Solid state physics- study of single crystal
• Bioscience-bonding in Protein, peptide with ligand
Phys. Rev. B 94, 174107 REVIEW L. J. Gamble , Anal. Chem. 2006 , 78 , 3316
12. AR
•ADF Calculation of NEXAFS using spin-orbit coupling TDDFT or the Slater-TS
method.
•FDMNES Calculation of NEXAFS using finite difference method and full multiple
scattering theory.
•FEFF8 Calculation of NEXAFS using full multiple scattering theory.
•MXAN NEXAFS fitting using full multiple scattering theory.
•FitIt NEXAFS fitting using multidimensional interpolation approximation.
•PARATEC NEXAFS calculation using plane-wave pseudopotential approach
•WIEN2k NEXAFS calculation on the basis of full-potential (linearized) augmented
plane-wave approach.
Software for NEXAFS analysis
https://www.wikiwand.com/en/X-ray_absorption_near_edge_structure
