Anomalous lattice dynamics and thermal properties of supported size- and shape-selected Pt nanoparticles

Anomalous lattice dynamics and thermal behavior have been observed for ligand-free, size-, and shapeselected Pt nanoparticles NPs supported on nanocrystalline -Al2O3 via extended x-ray absorption finestructure spectroscopy. Several major differences were observed for the NPs with respect to bulk Pt: i a contraction in the interatomic distances, ii a reduction in the dynamic temperature-dependent bond-length disorder and associated increase in the Debye temperature D , and iii an overall decrease in the bond-length expansion coefficient coupled with NP stiffening. The increase in the Debye temperature is explained in terms of the NP size, shape, support interactions, and adsorbate effects. For a similar average size, we observe a striking correlation between the shapes of the NPs and their D values.