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DS: Fachverband Dünne Schichten

DS 35: Biomolecular and Functional Organic Layers I (Focused Session)

DS 35.1: Topical Talk

Donnerstag, 25. März 2010, 17:15–17:45, H2

Surface enhanced infrared spectroscopy - pushing the detection limit towards zeptomolar sensitivity — •Frank Neubrech, Daniel Weber, Jörg Bochterle, and Annemarie Pucci — Kirchhoff - Institut für Physik, Universität Heidelberg

Surface enhanced infrared absorption (SEIRA) of molecules on metal films is known for many years but is still suffering from too small enhancement factors. Similar to surface enhanced Raman scattering, the electromagnetic field enhancement gives the main contribution to SEIRA signals. For adsorbates on metal nanoparticle-films average enhancement factors of more than three orders of magnitude were obtained. If metal nanoantennas are involved, the magnitude of the near-field amplitude at the fundamental (and also higher order) plasmon resonance reaches some ten times the external field value and therefore lowers the detection limit significantly. To analyse this kind of SEIRA quantitatively, well-defined monolayers of octadecanethiol on nanoantennas were investigated by means of infrared micro-spectroscopy. For individual nanoantennas, we have proven extraordinary enhancement factors up to 500 000 (ratio between enhanced infrared signal size and infrared absorption of the same number of molecules). The enhanced vibration signals show Fano-type line shapes due to dipolar coupling between molecular and plasmonic excitations.[1] Further increase of enhancement factors via near-field confinement in nanogaps of resonant nanoantenna arrays is under investigation.[2]

[1] F. Neubrech et al, Phys. Rev. Lett. 101, 157403, 2008.

[2] A. Pucci et al, submitted to Phys. Stat. Sol (B) 2009.