Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 60: Symposium: Bimetallic Nanosystems: Tuning Physical and Chemical Properties I (Invited Speakers: Harald Brune, Michael Hilgendorff, Konstantin Neyman)

O 60.2: Invited Talk (no funding)

Thursday, February 28, 2008, 10:00–10:30, MA 005

Magnetic-Noble Metal Nanocomposites with Size-Dependent Magnetic Properties and Morphology-Dependent Optical Response — •Michael Hilgendorff — caesar research center, Bonn, Germany

This talk aims at presenting the preparation and the properties of bimetallic magnetic AgCo, PtCo, and PdCo core/shell nanocrystals and Au-CoPt3, Ag-CoPt3, and Au-FePt heterodimers.

Stable bimetallic AgCo, PtCo, and PdCo core/shell colloids with a narrow particle size distribution and a controlled shell-thickness have been obtained in organic solvents (toluene, diethylether or dioctylether) by means of wet chemistry. All three bimetallic particle systems are ferromagnetic at low temperatures and superparamagnetic at room temperature. Coercivity, blocking temperature, and oxidation stability depend on the thickness of the Co-shell.

The bimetallic heterodimers have been prepared by a seeded-growth approach in the presence of a cationic surfactant (cetyltrimethylammonium bromide, CTAB). Hydrophobic CoPt3 and FePt nanoparticles were transferred into water using CTAB as a phase-transfer agent and were subsequently used as seeding materials for the reduction of gold and silver precursors to produce the nanocomposites. Through the modification of the growth conditions, Au-CoPt3 nanocomposites with various morphologies (spheres, cubes, rods) were prepared, providing an opportunity to tailor the optical response of these composite nanoparticles while maintaining the magnetic properties of the original seeds, even upon phase transfer into water.