Dresden 2009 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 38: Nano-optics of metallic and semiconducting nanostructures (experiments I)
O 38.8: Vortrag
Mittwoch, 25. März 2009, 16:45–17:00, SCH A216
Near-Field Investigation of Plasmonic Nano-Wire Eigenmodes — •Jens Dorfmüller1, Ralf Vogelgesang1, and Klaus Kern1,2 — 1Max Planck Institute for Solid State Research, 70569 Stuttgart, Germany — 2Ecole Polytechnique Fédérale de Lausanne, 1015 Lausanne, Switzerland
We use apertureless Scanning Near-Field Optical Microscopy (aSNOM) with cross-polarization of the excitation and scattered radiation, which allows us to map nearly unperturbed eigenmodes of plasmonic nanostructures. We study optical wire antennas produced by electron beam lithography. In contrast to far-field measurements, aSNOM allows us to compare plasmon resonances of many individual single wires simultaneously on a relatively small substrate area. We show measured amplitude and phase maps of the z-component of electromagnetic near-fields around these nano-structures.
Our amplitude images show lobes which indicate a strong z-component of the electromagnetic field and neighbouring lobes show a phase difference of 180∘ in the phase image. Depending on their size, the wires show multipolar resonances. The dipolar resonance is observed at a wire length ≈ λvac/5.6 and higher order resonances at odd multiples of the dipolar resonance length. Higher multipole orders, show less near-field intensity but a broader resonance in the wire-length domain.
We show that it is possible to break the symmetry of the exciting electromagnetic field by turning the sample and excite the otherwise symmetry forbidden even modes.