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O: Fachverband Oberflächenphysik

O 12: Nanostructures at Surfaces II (Wires, Tubes)

O 12.11: Vortrag

Montag, 26. März 2007, 16:45–17:00, H36

Local crystal structure of iron oxide nano particles synthesized form ferritin — •Michael Krispin, Marcus Preisinger, Peter Pfalzer, and Siegfried Horn — Lehrstuhl für Experimentalphysik II, Universität Augsburg, D-86135 Augsburg

We have investigated the size dependence of the local crystal structure of nanosized iron oxide by extended x-ray absorption fine structure (EXAFS) at the iron K-edge. Hematite (α-Fe₂O₃) nanoparticles of different diameters were produced by thermal treatment of horse spleen ferritin molecules and remineralized apo-ferritin molecules, respectively. The structure of these particles was compared to α-Fe₂O₃ and γ-Fe₂O₃ nanopowder references. The Fourier transformed EXAFS spectra of the nanoparticles differ significantly from hematite and maghemite reference spectra and change systematically as a function of particle diameter, signalling a corresponding evolution of the structure. We show that the Fe-O bond length decreases with decreasing diameter of the particles and with decreasing particle density. This is explained by a core-shell model, in which the fraction of a γ-Fe₂O₃ like particle shell increases while the α-Fe₂O₃ core decreases with decreasing particle size.