8 February 2007 Metallic colloids and their plasmonic properties
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Colloidal growth of plasmonic nanostructures may present some advantages such as shape control at the nm scale with atomic smoothness of the surfaces and possibly reduced damping. We show that the seed-mediated growth of gold nanostructures is strongly dependent on the gold seed nanocrystal structure. Starting with gold seed solutions prepared such that they are either single crystalline or multiply twinned, growth yields either nanorods with good control over the aspect ratio (~10%) or elongated bipyramidal nanoparticles. The nanorods are single crystalline while the gold bipyramids are penta-fold-twinned. The gold bipyramids are also strikingly monodisperse in shape with the sharpest ensemble surface plasmon resonance reported so far. Silver can be coated onto the gold nanostructures leading to a large blue-shift of the longitudinal plasmon resonance. Surprisingly, even a thin silver layer introduces much additional damping explained as scattering at the Au/Ag interface. Silver can be converted to silver sulphide yielding a large red-shift. The metal-semiconductor composite materials may present interesting nonlinear optical properties which are being currently investigated. Finally, the nonlinear optical scattering from individual Au nanorods was measured under excitation by ultrafast laser pulses on resonance with their longitudinal plasmon mode. Surprisingly, the ultrafast nonlinearity can be attributed entirely to the heating of conduction electrons and does not exhibit any response associated with coherent plasmon oscillation. This indicates an unanticipated damping of strongly driven plasmons.
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Mingzhao Liu, Mingzhao Liu, Matthew Pelton, Matthew Pelton, Norbert F. Scherer, Norbert F. Scherer, Philippe Guyot-Sionnest, Philippe Guyot-Sionnest, } "Metallic colloids and their plasmonic properties", Proc. SPIE 6471, Ultrafast Phenomena in Semiconductors and Nanostructure Materials XI and Semiconductor Photodetectors IV, 647107 (8 February 2007); doi: 10.1117/12.706196; https://doi.org/10.1117/12.706196

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