Model-Independent Imaging of
Elemental Distributions at Interfaces with RAXR
Resident anomalous x-ray reflectivity (RAXR) is an ideal tool for probing the liquid-solid
interface. It has both geometrical and spectroscopic sensitivities, as well
as interfacial and elemental specificities. It is particularly powerful as a
way to observe an element-specific component of interfacial reactions at
complex (e.g., solid-liquid) interfaces.
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(A) Schematic of a solid-liquid interface with an
adsorbed species whose location is unknown (e.g., sites 1 through
9). (B) X-ray absorption spectrum of an element with an absorption
edge position, Eo. (C) Resonant anomalous X-ray reflectivity spectra
for atom locations 1-9. The shape of each spectra is determined by a
combination of the known absorption spectrum and the unknown atom
distribution. |
- We have demonstrated a robust formalism to image elemental distributions
at interfaces directly from X-ray scattering data with sub-Å vertical
spatial resolution.
- This is achieved from resonant anomalous X-ray reflectivity (RAXR) data,
where the phase-sensitivity derives from the anomalous dispersion of X-rays
near a characteristic absorption edge. This phase-sensitivity is used to
create “model-independent” images of the elemental distribution by discrete
Fourier synthesis, as demonstrated previously in X-ray standing wave
imaging.
- The approach was validated by imaging the differences in distributions
of mono- and di-valent cations at the muscovite-water interface.
Reference
C. Park and P. A. Fenter, “Phasing of Resonant Anomalous X-ray Reflectivity
Spectra and Direct Fourier Synthesis of Element-Specific Partial Structures at
Buried Interfaces,” Journal of Applied Crystallography, 40 282-289 (2007). |
