Berlin 2008 – wissenschaftliches Programm

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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 60.7: Vortrag

Donnerstag, 28. Februar 2008, 11:45–12:00, MA 005

Optical properties of supported core-shell and alloy silver/gold nanoparticles — •Frank Hubenthal and Frank Träger — Universität Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany

For many applications like surface enhanced Raman scattering in which the optical field enhancement associated with surface plasmon excitation is exploited, tunability of this collective resonance over a wide range is required. For this purpose we have prepared core-shell and alloy nanoparticles consisting of Ag and Au. The core-shell nanoparticles were made by subsequent deposition of Ag and Au atoms and vice versa on dielectric substrates followed by diffusion and nucleation. One of the most interesting among the numerous results is that the plasmon frequency can be tuned from 2.8 eV (442 nm) to 2.1 eV (590 nm) depending on the Au shell thickness. Subsequent annealing of the core-shell nanoparticles causes a shift of the resonance frequency to 2.6 eV. Theoretical modelling allows us to attribute this observation to the formation of alloy nanoparticles. Finally, we have measured the dephasing time T2 of the alloy nanoparticles by means of spectral hole burning. T2 amounts to 8.1 +/- 1.6 fs, in good agreement with the dephasing time T2 = 8.9 fs that is included in the dielectric function of the bulk.