Dresden 2011 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 50: Plasmonics and Nanooptics V
O 50.4: Vortrag
Mittwoch, 16. März 2011, 15:45–16:00, WIL A317
Plasmonic sensing using multipolar infrared antenna resonances — •Frank Neubrech1, Daniel Weber1, Jörg Bochterle1, Gui Han2, Tadaaki Nagao2, and Annemarie Pucci1 — 1Kirchhoff-Institute for Physics, Heidelberg University, Germany — 2National Institute for Materials Science, Tsukuba, Japan
Excited resonantly, antenna-like nanostructures confine the electromagnetic radiation on the nanoscale and therefore enhance the electromagnetic field in their vicinity, which can be exploited for surface enhanced infrared spectroscopy. The only precondition is a good match between the fundamental resonant excitation of the nanoantenna and the vibrational signal of the adsorbate of interest. But not only the near field of the fundamental mode can be used to enhance vibrational signals, but also multipolar modes (l=3, 5, 7) as we will show in this contribution. We performed infrared spectroscopic measurements of nanoantennas supported by a silicon wafer with a natural SiO2 layer. For parallel polarized light and at a good match of the fundamental resonance mode of the antenna with the SiO2 phonon, the SiO2 surface phonon-polariton signal is enhanced. Its line shape reveals a Fano-type interaction with the antenna resonance. Detuning the nanoantenna by increasing its length leads to a decrease of the SiO2 signal due to the frequency dependence of the antenna resonance. For even longer antennas the SiO2 signal increases again and reaches a second maximum if the multipolar l=3 excitation of the nanoantenna matches the excitation frequency of the SiO2 phonon-polariton.