## Element-specific structure of materials with intrinsic disorder by high-energy resonant x-ray diffraction and differential atomic pair-distribution functions : a study of PtPd nanosized catalysts.

We demonstrate how high-energy resonant x-ray diffraction (XRD) and differential atomic-pair-distribution function (PDF) analysis can be used to characterize the atomic ordering in materials of limited structural coherence with both excellent spatial resolution and element specificity. First we prove that this experimental approach is feasible by probing the K-absorption edge of Au({approx}81 keV) atoms in chemically ordered and disordered bulk Cu3Au alloys. The resulting Au-differential PDFs show very clearly the different ways Au atoms are known to occupy the sites of otherwise identical cubic lattices of those materials. Next we apply it to a more complex material: PtPd alloy andmore »