Modulated excitation extended X-ray absorption fine structure spectroscopy.

Area of Science:

• Materials Science
• Spectroscopy
• Surface Chemistry

Background:

• Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy is sensitive to local atomic structure.
• Minute structural changes can be challenging to detect with conventional EXAFS.
• Modulated excitation and phase-sensitive analysis offer potential for enhanced sensitivity.

Purpose of the Study:

• To simulate and understand the impact of phase-sensitive analysis on EXAFS spectra.
• To investigate the reversible partial oxidation of Palladium (Pd) to Palladium Oxide (PdO).
• To validate simulation results with in situ experimental data.

Main Methods:

• Simulated modulated EXAFS experiments with varying coordination number, interatomic distance, and Debye-Waller factors.
• Phase-sensitive detection (PSD) applied to EXAFS data.
• In situ EXAFS experiments at the Pd K-edge during H2/O2 modulation at 573 K.

Main Results:

• Phase-sensitive analysis successfully separated subtle structural signals, like the formation of a Pd-(O)-Pd shell.
• The PdO shell formation on a metallic Pd core was identified during rapid H2 to O2 switching.
• Simulations accurately predicted the experimental observations.

Conclusions:

• Phase-sensitive detection significantly improves the ability to resolve minor structural contributions in EXAFS.
• The study provides a framework for analyzing phase-resolved EXAFS spectra of functional materials.
• This approach offers a more detailed understanding of dynamic processes in materials.