Ultrafast Dynamics of metallic nanorod arrays and their interaction with quantum dots and dye molecules
Zusammenfassung der Projektergebnisse
The optical properties of two-dimensional arrays of gold nanorods standing perpendicular on a substrate are governed by surface plasmon resonances. We performed two-color femtosecond pump-probe spectroscopy in a transient-transmission arrangement to elucidate the response of nanorod arrays to femtosecond optical excitation. We found that first – depending on the surface plasmon resonance frequency – a rapid red- or blue-shift of the plasmon resonance occurs around 100 fs after the pump pulse. Then, within 300 fs the resonance broadens and its amplitude weakens before it recovers to its static value on a much longer timescale (>10 ps). We were able to trace back this behavior of the plasmonic resonance to pump-induced material modifications such as interband transitions, electronelectron scattering, or electron-phonon interactions. By parameterizing the gold dielectric function within the framework of a Drude critical-point model with physically well justified parameters and by connecting the material properties to the optical properties of the nanorod array by means of a dipolar interaction model, a very good fit could be achieved between the transients calculated within this model and the experimentally observed ones. The analysis revealed that a critical point at the interband transition energy of gold is crucial for the transient dynamics. The changes of the dielectric function as deduced from the data within the model calculations also agree well with calculations from the literature. One important result of our investigations is that no extraordinary additional effect is needed to explain the ultrafast signal observed close to the inflection points of the spectral profile of the plasmon, but that also this signal is well accounted for by the model. For the time-resolved simulation of the interaction of femtosecond laser pulses with metal nanostructures we improved the discontinuous Galerkin method by describing the geometry by curved elements rather than by the usual triangles or tetrahedrons. Curved elements turned out to be absolutely necessary to avoid artifacts caused by the unphysically sharp corners that occur when the metal structure is discretized by triangles or tetrahedrons. As to the fabrication of metal nanorod arrays by electroplating in a porous alumina layer on a gold underlayer, we investigated the growth of nanorods on prestructured underlayers. We found that the nanorod carpet does not reach all the way up to the edge of the gold underlayer, but a rod-free micrometer-wide depletion zone forms along the edge. At the same time the very edge becomes decorated by a single line of nanorods (”nanofence”).
Projektbezogene Publikationen (Auswahl)
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Improving Nano-Optical Simulations Through Curved Elements Implemented within the Discontinuous Galerkin Method, Journal of Computational and Theoretical Nanoscience 7 (2010) 1581–1586
A. Hille, R. Kullock, S. Grafström, L. Eng
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Metallic nanorod arrays: negative refraction and optical properties explained by retarded dipolar interactions, J. Opt. Soc. Am. B 27 (2010) 1819–1827
R. Kullock, S. Grafström, P.R. Evans, R.J. Pollard, L. Eng
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SHG simulations of plasmonic nanoparticles using curved elements, Optics Express 19 (2011) 14426–14436
R. Kullock, A. Hille, A. Haussmann, S. Grafstr¨m, L.M. Eng
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Utilizing Dog-Boning to Build up High-Aspect-Ratio Nanofences, Journal of The Electrochemical Society 161 (2014) D26-D30
G. Scheunert, V. Hoffmann, R. Kullock, J.R. Whyte, R. Kirchner, S. Grafström, W.-J. Fischer, L.M. Eng
