Limits and Advantages of X-ray Absorption Near Edge Structure for Nanometer Scale Metallic Clusters
Résumé
We consider the analysis of the K edge of 3d or 4d transition metals when nanometer-scale metallic clusters are considered. From a practical point of view, numerical simulation of the XANES part of the K absorption spectrum of most elements of the periodic table can be performed through full multiple scattering calculations. Then, on the basis of a linear combination of the XANES spectra of reference compounds, the presence of the different phases present inside the materials can be quantified. Here, we show that for nanometer scale metallic clusters, it is not sufficient to consider only the electronic state of the metal of interest to perform a linear combination analysis. In the case of these peculiar materials, special attention has to be paid to different structural parameters, for example, the size and morphology of the cluster, the interatomic distance (taking into account contraction/dilatation processes), and the presence of heterometallic bonds (in the case of bimetallic clusters). Moreover, this approach is not specific to the metallic state. As a conclusion, the quantitative measurement of the structural parameters coming from EXAFS analysis constitutes an invaluable starting point for the FEFF-PCA simulation. The fact that major results coming from the emergence of dynamical studies, namely, Quick-EXAFS or energy dispersive EXAFS, are now obtained will lead to significant breakthroughs in the understanding of the genesis/reactivity of nanometer-scale entities.