title: Structural and architectural evaluation of bimetallic nanoparticles: a case study of Pt-Ru core-shell and alloy nanoparticles.
abstract: A comprehensive structural/architectural evaluation of the PtRu (1:1) alloy and Ru@Pt core-shell nanoparticles (NPs) provides spatially resolved structural information on sub-5 nm NPs. A combination of extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), pair distribution function (PDF) analyses, Debye function simulations of X-ray diffraction (XRD), and field emission transmission electron microscopy/energy dispersive spectroscopy (FE-TEM/EDS) analyses provides complementary information used to construct a detailed picture of the core/shell and alloy nanostructures. The 4.4 nm PtRu (1:1) alloys are crystalline homogeneous random alloys with little twinning in a typical face-centered cubic (fcc) cell. The Pt atoms are predominantly metallic, whereas the Ru atoms are partially oxidized and are presumably located on the NP surface. The 4.0 nm Ru@Pt NPs have highly distorted hcp Ru cores that are primarily in the metallic state but show little order beyond 8 A. In contrast, the 1-2 monolayer thick Pt shells are relatively crystalline but are slightly distorted (compressed) relative to bulk fcc Pt. The homo- and heterometallic coordination numbers and bond lengths are equal to those predicted by the model cluster structure, showing that the Ru and Pt metals remain phase-separated in the core and shell components and that the interface between the core and shell is quite normal.
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland 20742, USA.
authors.forename: Selim
authors.initials: S
authors.lastname: Alayoglu
authors.forename: Peter
authors.initials: P
authors.lastname: Zavalij
authors.forename: Bryan
authors.initials: B
authors.lastname: Eichhorn
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.forename: Anatoly I
authors.initials: AI
authors.lastname: Frenkel
authors.forename: Peter
authors.initials: P
authors.lastname: Chupas
mesh_terms: D000497:Alloys / Q000737:chemistry*; D053768:Metal Nanoparticles / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D010084:Oxidation-Reduction; D010316:Particle Size; D010984:Platinum / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*; D056928:X-Ray Absorption Spectroscopy; D014961:X-Ray Diffraction
chemical_list: D000497:Alloys; D010984:Platinum; D012428:Ruthenium