Advances in nanoparticle structure characterization by X-ray absorption spectroscopy

X-ray absorption fine structure (XAFS) spectroscopy has been used to study short range order in nanoparticles for four decades. Due to their role in catalysis, we briefly revisit their structural and compositional descriptors that affect their reactivity. Among the most frequently used descriptors are various attributes of structure, shape and compositional motifs (e.g., core-shell, random or cluster-by cluster). This talk will review new methods of data analysis and modeling of nm-scale nanoparticles and sub-nm clusters that extend beyond conventional fitting of experimental XAFS spectra. One recent method, based on parameter-free MD simulations, was validated on the example of Pd-Au nanoalloys containing about 100 atoms with narrow size and compositional distributions, where random mixing of Pd and Au atoms was demonstrated earlier by conventional Extended XAFS (EXAFS) analysis.¹ New Machine Learning approaches for “on the fly” analysis of X-ray Absorption Near Edge Structure (XANES) spectroscopy in ultra-small clusters will be presented for mono- and bimetallic alloys that are often investigated in operando conditions.
¹ J. Timoshenko, K. R. Keller, A. I. Frenkel J. Chem. Phys. 146, 114201 (2017) (2017 Editors’ Choice)