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MM: Fachverband Metall- und Materialphysik

MM 6: Topical Session TEM II

MM 6.2: Talk

Monday, March 14, 2011, 15:00–15:15, IFW A

Aberration-corrected imaging of binary metal nanoparticles — •Darius Pohl, Björn Bieniek, Elias Mohn, Ludwig Schultz, and Bernd Rellinghaus — IFW Dresden, Helmholtzstr. 20, D-01156 Dresden, Germany.

Aberration-corrected high resolution transmission electron microscopy (HRTEM) is used to study the lattice structure of single crystalline FePt and FeNi nanoparticles. Due to the delocalization-free imaging a direct and precise measurement of atom positions and lattice constants even at the very surface layers becomes feasible. For a wide range of particle sizes and morphologies, metallic nanoparticles of binary alloys are found to show an expansion of the lattice in the surface layers. In order to gain insight into the origin of the observed surface-near lattice expansion, molecular dynamics (MD) simulations were performed. A comparison of the experimental HRTEM images with the relaxed model structures clearly reveals that segregation phenomena are responsible for the dilated lattice at the particle surface.

In order to investigate the influence of oxygen on the surface-near lattice expansion, oxidation sensitive systems need to be investigated. Since FeNi is less noble and thus more susceptible to oxidation than FePt, the effect of structural changes due to oxidation should be much more pronounced in the former. From a comparison of un-oxidized and oxidized FeNi nanoparticles, the influence of oxygen on the surface-near lattice constant of the metallic particle core is determined to be almost negligible.