Nanoantenna enhanced FCS

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Surface enhanced Raman scattering on nanoantennas

Surface enhanced Raman scattering on a single nanometric aperture

We quantitatively evaluate single nanoapertures milled in optically thick gold films to determine the SERS enhancement factors using paramercaptoaniline as non-resonant analyte. We determine a peak enhancement factor of 5x10^4 for a single 100 nm diameter aperture.

This work has three major aspects of interest to the SERS community :

1) Nanoapertures milled in noble metal films form interesting SERS substrates thanks to their rational and tunable design, controlled surface enhancement, and intrinsic robustness. We discuss the different design parameters yielding to optimum SERS enhancement in a single aperture which can be used to further improve the SERS substrates with nanoaperture arrays.

2) We discuss different ways of expressing the SERS enhancement factor, and show excellent agreement between experimental results and
numerical simulations.

3) Most experimental studies of controlled SERS substrates skip the issue of the adhesion layer between the gold nanostructure and the glass substrate. We experimentally demonstrate that the adhesion layer has a crucial effect on the SERS enhancement, and needs to be fully considered while designing nanosubstrates for high-sensitivity spectroscopy.

Surface enhanced Raman scattering on a gold dimer nanoantenna

We are presently studying the SERS enhancement on nanoantennas made of clusters of colloidal gold nanoparticles. This study presents several advantages over the current state-of-the-art :

  • Colloidal self-assembly assisted by nanowetting (collaboration LTM BioColloNa) is a versatile bottom-up approach for creating large scale SERS antennas with high reproducibility.
  • Confocal Raman microscopy coupled to rigorous numerical analysis enables a reliable quantification of the SERS enhancement factor, which is a requisite to investigate chemical effects occuring in SERS such as charge transfers.

Custom home-made confocal Raman microscope

The home-built confocal Raman microspectrometer used in this study is based on an inverted microscope with 40x 1.3NA oil immersion objective. The excitation source is provided by a continuous wave HeNe laser operating at 632.8 nm. The Raman scattered light is collected by the same microscope objective, and is further separated from the excitation laser and elastically scattered light by a set formed by a dichroic mirror, long-pass filter and holographic notch filter. A 50 µm pinhole conjugated to the microscope objective focal plane rejects the out-of-focus light, and defines a confocal volume calibrated to 0.75 fL. The Raman signal is then directed towards a Jobin-Yvon 270M spectrometer coupled with a liquid-nitrogen cooled CCD camera. The spectrometer entrance slit is conjugated to the confocal pinhole with a 1:1 magnification. This configuration allows for all the light passing through the confocal pinhole to enter the spectrometer with the optimum spectrometer resolution of 0.3 nm.

People involved

  • Jerome Wenger
  • Richard Hostein (now assistant professor Paris VI university)
  • Nadia Djaker (now assistant professor Paris XIII university)

Selected Reference

  • N. Djaker, R. Hostein, E. Devaux, T. W. Ebbesen, H. Rigneault, and J. Wenger, "Surface enhanced Raman scattering on a single nanometric aperture", J Phys Chem C 114, 16250-16256 (2010). - PDF

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