TY - JOUR A1 - Han, Luyang A1 - Wiedwald, Ulf A1 - Biskupek, Johannes A1 - Fauth, Kai A1 - Kaiser, Ute A1 - Ziemann, Paul T1 - Nanoscaled alloy formation from self-assembled elemental Co nanoparticles on top of Pt films JF - Beilstein Journal of Nanotechnology N2 - The thermally activated formation of nanoscale CoPt alloys was investigated, after deposition of self-assembled Co nanoparticles on textured Pt(111) and epitaxial Pt(100) films on MgO(100) and SrTiO3(100) substrates, respectively. For this purpose, metallic Co nanoparticles (diameter 7 nm) were prepared with a spacing of 100 nm by deposition of precursor-loaded reverse micelles, subsequent plasma etching and reduction on flat Pt surfaces. The samples were then annealed at successively higher temperatures under a H2 atmosphere, and the resulting variations of their structure, morphology and magnetic properties were characterized. We observed pronounced differences in the diffusion and alloying of Co nanoparticles on Pt films with different orientations and microstructures. On textured Pt(111) films exhibiting grain sizes (20–30 nm) smaller than the particle spacing (100 nm), the formation of local nanoalloys at the surface is strongly suppressed and Co incorporation into the film via grain boundaries is favoured. In contrast, due to the absence of grain boundaries on high quality epitaxial Pt(100) films with micron-sized grains, local alloying at the film surface was established. Signatures of alloy formation were evident from magnetic investigations. Upon annealing to temperatures up to 380 °C, we found an increase both of the coercive field and of the Co orbital magnetic moment, indicating the formation of a CoPt phase with strongly increased magnetic anisotropy compared to pure Co. At higher temperatures, however, the Co atoms diffuse into a nearby surface region where Pt-rich compounds are formed, as shown by element-specific microscopy. KW - alloy KW - CoPt KW - HRTEM KW - nanoparticles KW - XMCD KW - Co KW - epitaxy KW - magnetometry KW - Pt Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-142869 VL - 2 ER - TY - THES A1 - Blömer, Steffen T1 - Synthese von modifizierten Eisenoxid-Nanopartikeln für die MR-Tomographie T1 - Synthesis of modified iron oxide nanoparticles for MRI N2 - In der vorliegenden Arbeit wurden magnetische Kolloide auf der Basis von Eisenoxid-Nanopartikeln hergestellt, die eine erhöhte Verweildauer im Blutstrom aufweisen sollten. Die Hüllmoleküle bestehen aus zwei Teilen: Direkt an den Phosphor gebunden eine hydrophobe Alkylkette aus vier bis zehn CH2-Einheiten, und daran anschließend eine Methoxy-terminierte Polyethylenglykol (PEG)-Kette. Die PEG-Kette sollte sowohl die Hydrophilie der fertigen Partikel als auch den nötigen Schutz gegen Phagozytose gewährleisten. Diese speziellen Phosphonsäuren wurden dann dazu verwendet, Magnetit-Nanopartikel stabil einzuhüllen. N2 - The present dissertation deals with the preparation of magnetic colloids on the basis of iron oxide nanoparticles exhibiting an extended lifetime in the bloodstream. The coating molecules were made up of two parts: A hydrophobic alkyl chain of four to ten CH2 groups, and a methoxy-terminated polyethyleneglycol (PEG) chain. The PEG chain was included to make the particles hydrophilic and to protect them from phagocytosis. These specially designed phosphonic acids were then used to coat magnetite nanoparticles. KW - Eisenoxide KW - Nanopartikel KW - NMR-Tomographie KW - Kontrastmittel KW - Polyethylenglykole KW - Magnetresonanztomographie KW - PEG KW - iron oxide KW - nanoparticles KW - MRI KW - contrast agent Y1 - 2011 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-66068 ER -