Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 49: Particles and Clusters
O 49.3: Vortrag
Mittwoch, 27. Februar 2008, 15:45–16:00, MA 005
Ensemble-modelling of CdSe/ZnS core-shell nanoparticles using x-ray powder diffraction data — •Franziska Niederdraenk1, Christian Kumpf1, Reinhard Neder2, and Eberhard Umbach1,3 — 1Universität Würzburg, Experimentelle Physik II, 97074 Würzburg — 2Universität Würzburg, Mineralogisches Institut, 97074 Würzburg — 3Forschungszentrum Karlsruhe GmbH, D-76021 Karlsruhe
Standard methods for the analysis of powder x-ray diffraction data (like e.g. a Rietveld refinement) cannot be used efficiently for heterogenic or imperfect systems like core-shell nanoparticles, since they are usually based on bulk-crystal approaches. In particular, mixed (epitactic) structures, interface-effects, and imperfections like relaxations and stacking faults, that often occur in very small particles (<3 nm), cannot be handled. In order to overcome these limitations we developed a bottom-up approach which models the entire nanoparticle including the shell, and hence takes all structural features implicitly into account. The Debye formula is used to calculate the corresponding diffraction pattern. Furthermore a size distribution for the nanoparticles is considered by applying ensemble averaging.
We present data from CdSe particles with a diameter of ~4 nm and a ZnS shell of nominally ~1 nm thickness. Different shapes and different shells for the particles were tested, as well as all relevant structural parameters refined. The best model consists of an elliptical CdSe core with a non-epitaxial ZnS shell which does not cover the core-surface completely.