Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 42: Poster Session II (Nanostructures at surfaces: arrays; Nanostructures at surfaces: Dots, particles, clusters; Nanostructures at surfaces: Other; Nanostructures at surfaces: Wires, tubes; Metal substrates: Adsorption of O and/or H; Metal substrates: Clean surfaces; Metal substrates: Adsorption of organic/bio moledules; Metal substrates: Solid-liquid interfaces; Metal substrates: Adsorption of inorganic molecules; Metal substrates: Epitaxy and growth; Heterogeneous catalysis; Surface chemical reactions; Ab-initio approaches to excitations in condensed matter; Organic, polymeric, biomolecular films– also with adsorbates; Particles and clusters)

O 42.118: Poster

Mittwoch, 25. März 2009, 17:45–20:30, P2

Crystal structure of iron oxide nano particles synthesized form ferritin — •Michael Krispin, Aladin Ullrich, and Siegfried Horn — Lehrstuhl für Experimentalphysik II, Universität Augsburg, D-86135 Augsburg

We have investigated the local crystal structure of nanosized iron oxides by extended x-ray absorption fine structure (EXAFS). Iron oxide nanoparticles of different diameters were produced by thermal treatment of horse spleen ferritin molecules and remineralized apo-ferritin molecules, respectively. The size was determined by atomic force microscopy (AFM) as well as transmission electron microscopy (TEM). The structure of these particles was compared to various iron oxide and ferrihydrite references. The Fourier transformed (FT) EXAFS spectra of the iron oxide nanoparticles differ significantly from α-Fe₂O₃ and γ-Fe₂O₃ reference spectra and change systematically as a function of particle diameter, signalling a corresponding evolution of the structure. A possible explanation could be the occurrence of a mixture of α-Fe₂O₃ and γ-Fe₂O₃ phases in a core-shell model, i.e. the particle consists of a α-Fe₂O₃ core and γ-Fe₂O₃ like shell. A decrease of core to shell ratio with decreasing particle size may then explain the changes in the measured FT-EXAFS. Indeed, EXAFS oscillations of samples can be fitted by a linear combination of the EXAFS oscillations of the measured α-Fe₂O₃ and γ-Fe₂O₃ reference powders. This picture is supported by the fact, that x-ray diffraction (XRD) measurements on annealed native ferritin show that the α and γ phases coexist.