EXAFS as a tool for studies of bimetallic PdCo nanocluster structure

Abstract

Structure of metallic palladium, cobalt and 50 at.% Pd–50 at.% Co model nanoclusters of cubooctahedral and icosahedral shapes and sizes 1.0–3.0 nm has been optimized using Sutton–Chen potentials. Short range order structure parameters calculated for f.c.c. lattice, cubooctahedral and icosahedral monometallic clusters are discussed. EXAFS spectra for Co K-edge and Pd K-edge for the model clusters were calculated. Standard EXAFS analysis of these spectra was performed and the results are compared with structural parameters directly calculated from atomic positions of these relaxed model clusters. It is discussed how modifications of the atomic pair distribution function affect the EXAFS spectra. The results on these model structures indicate that to obtain meaningful information on the Pd–Co alloy system very precise measurements of both: Pd and Co absorption edges are required. It is also demonstrated that the correct interpretation of the measured EXAFS spectra requires use of a modeling procedure.