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Basic Introduction of XANES and EXAFS
- 1. Fundamental of XAS Presented by Amlan Roy Research Scholar, Department of Energy Scien Engineering (DESE) IIT Bombay, Powai-400076 Mumbai, India
- 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