Structure and Dynamics of Applied Nanomaterials

Illuminating Surface Atoms in Nanoclusters by Differential X-ray Absorption Spectroscopy

We use differential extended x-ray absorption fine structure (Δ-EXAFS) to monitor the Ar-induced surface restructuring of silica-supported Pd nanoclusters (1 nm diameter) at 77 K.  Δ-EXAFS analysis shows 9 ± 2 nearest-neighbor Pd-Pd bonds expand by 0.104 ± 0.005 Å as a result of Ar adsorption.  Atomistic molecular dynamics simulations provide evidence for a model in which Ar drives restructuring of under-coordinated Pd atoms, leading to an increased Pd-Pd bond length of surface Pd atoms with no change in overall nearest-neighbor Pd-Pd coordination number.  Based on observations from the atomistic simulations, it is likely that under-coordinated atoms are trapped in metastable states at 77 K and Ar provides the kinetic energy needed to overcome the barrier for surface restructuring.  Together, experiment and theory highlight the ability of Δ-EXAFS to probe surface atoms of Pd nanoclusters.

C. S. Spanjers, T. P. Senftle, A. C. T. van Duin, M. J. Janik, A. I. Frenkel, R. M. Rioux
Illiuminating surface atoms in nanoclusters by differential X-ray absorption spectroscopy
(Invited) Phys. Chem. Chem. Phys., 16, 26528-26538 (2014)