Can anyone explain how does such a relaxation process effect the XAS or XPS peak position, I have tried to obtain materials online however those available seems to be filled with mathematical complexities. I need some help!
Dinesh... In XPS spectra, measured core level binding energies, Eb, involve both the ground state and the final state relaxation energies. The response of spectator electrons to the creation of a core hole and the Auger deexcitation process causes lowering of the measured binding energy as compared to the initial state (i.e. chemical shift) binding energy and this final state relaxation energy R can vary with chemical environment.
Hence, there is a need to distinguish between initial and final state contributions to the measured binding energies. It is therefore important that final state effects are correctly described if binding energy shifts are to yield useful and reliable chemical information as to the electronic structure of transition metals and their compounds.
Experimentally, relaxation energy shifts are often estimated by measuring the Auger parameter shift defined by:
Δα' = ΔEb + ΔEk
It is usually assumed, following the derivation by Morretti, that the relaxation energy for the doubly core-ionized state created by the Auger process, equals 2R, leading to:
Δα' ≈ 2ΔR
http://www.cem.msu.edu/~cem924sg/Topic10.pdf
Without core hole relaxation, the binding energy of a core level would appear at a higher value as the coulomb attraction of the created hole on the emitted photoelectron would be larger. Due to the response on the presence of the positive charge of the core hole by all other charges and dipoles around (relaxation), the core hole charge is screened to some extend, leading to a smaller actual measured binding energy of the core level.
Dear Kumar,
In brief:
Initial-state effects, it is the charge on the atom prior to photoemission that plays the major role in the determination of the magnitude of the chemical shift.
Final-state effects that occur following photoelectron emission, such as core hole screening, relaxation of electron orbitals and the polarization of surrounding ions are often dominant in influencing the magnitude of the chemical shift.
More detailed it is explained in the attached review and second manuscript on the base of theoretical background.
Hope it will be useful.
With the best regards,
Dmitry
Dear All,
Thank you so much for the help you have given. I have learnt a lot through you, with your giudance I think I know a bit know about core hole excitation and relaxation processes.
Sincerely
Dinesh
A nice example of final state/hole screening effect is the different O1s binding energy of H2O in the liquid phase and gas phase. Due to less density of the molecules, the created core hole is less screened in the gas phase and appears at about 2.5 eV higher binding energy than from the liquid phase.
Article Direct Observation of the Energetics at a Semiconductor/Liqu...
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