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Nonstoichiometric intensities in core photoelectron spectroscopy
J Söderström1, N Mårtensson, O Travnikova
1Department of Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden.
Physical Review Letters
|September 26, 2012
Summary
Apparent stoichiometry in X-ray photoemission spectroscopy is affected by photoelectron scattering and energy losses. This study reveals deviations from expected ratios, impacting elemental analysis in various research fields.
Area of Science:
- Atomic and Molecular Physics
- Surface Science
- Spectroscopy
Background:
- X-ray photoemission spectroscopy (XPS) is widely used to determine sample stoichiometry.
- Stoichiometry determination in XPS typically assumes ionization cross sections are independent of molecular environment.
Purpose of the Study:
- To investigate apparent carbon stoichiometry in chlorine-substituted ethanes using XPS.
- To understand deviations from expected stoichiometric ratios and their underlying causes.
Main Methods:
- Gas-phase XPS experiments on chlorine-substituted ethanes.
- Analysis of C1s ionization spectra across a range of photon energies.
- Modeling photoelectron scattering using multiple-scattering EXAFS calculations.
- Inclusion of shakeup/shakeoff and inelastic scattering effects in the model.
Main Results:
- Observed nonstoichiometric carbon ratios across various photon energies.
- Spectra exhibited X-ray-absorption fine structure (EXAFS)-like oscillations.
- Apparent stoichiometry deviated significantly from expected values, especially at higher photon energies.
Conclusions:
- Photoelectron scattering and energy loss processes (shakeup, shakeoff, inelastic scattering) significantly impact apparent stoichiometry in XPS.
- The assumption of constant ionization cross sections is not universally valid.
- Accurate stoichiometric determination requires accounting for these complex electronic processes.
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