Regensburg 2013 – scientific programme

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O: Fachverband Oberflächenphysik

O 36: Poster Session II (Organic films and electronics, photoorganics; Nanostructures; Plasmonics and nanooptics, Surface chemical reactions and heterogeneous catalysis, Surface dynamics )

O 36.71: Poster

Tuesday, March 12, 2013, 18:15–21:45, Poster B2

HR-EELS on powder samples — •Sebastian Frey, Martin Kroll, and Ulrich Köhler — Ruhr-Universität Bochum

High resolution electron energy loss spectroscopy is a useful tool in heterogeneous catalysis as it provides information about vibrational states of adsorbates. While HR-EELS on single crystals has found wide spread and nowadays serves as a sophisticated tool to obtain adsorbate information, most studies on oxide nanoparticles rely on infrared spectroscopy (FTIRS) as EELS requires a reflecting sample with high conductivity. In the field of heterogeneous catalysis this causes a material gap between idealized single crystalline model systems (analyzed with HR-EELS) on the one hand and real catalysts based on nanoparticles (studied with FTIRS) on the other hand.

Enabling HR-EEL Spectroscopy on nanoparticles opens up a new approach to get closer insight into the behavior of real oxide materials that are used in heterogeneous catalysis. We studied ZnO nanoparticles and their corresponding metal loads Cu and Au, which are used for methanol synthesis and CO oxidation. Our experience shows that a thoroughly sample preparation and pretreatment is vital in order to obtain reasonable results in the EELS. The nanoparticle layer has to be smooth and closed to produce adequate reflection intensity. Moreover sufficient conductivity is required to prevent surface charging. Both requirements can be met by sedimenting oxide powder on a gold plate. In the case of ZnO a clear phonon spectrum emerges which is comparable to Fuchs-Kliewer phonons present on a single crystalline surface.