Multiscale 3D Patterning of Nanoparticle Assemblies for Plasmonic Devices

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1248-D09-09

Multiscale 3D Patterning of Nanoparticle Assemblies for Plasmonic Devices

R. Carles, C. Farcau, G. Benassayag, C. Bonafos, P. Benzo, L. Cattaneo, B. Pecassou and A. Zwick Groupe Nanomat – CEMES-CNRS – Université de Toulouse, 29 rue Jeanne Marvig, BP 94347, 31055 Toulouse Cedex 4, France

ABSTRACT We have developed a novel strategy for elaborating composite plasmonic nanomaterials in a well controlled manner. Combining several techniques commonly used in microelectronic engineering, namely sputtering deposition, thermal oxidation, ultra low energy ion implantation, focused ion beam lithography, thermal or laser annealing, we have obtained 3D patterned optical layers. Their spatial and spectral responses take benefit of optical interference, plasmonic resonance effects and coupling between excitations in both near and far field regime. Moreover these structures show high level of uniformity, reproducibility and stability, and they preserve flat and chemically uniform surfaces. INTRODUCTION The exploitation of the giant enhancement of electromagnetic coupling at the vicinity of a plasmonic antenna needs to control the patterning of the supporting devices at different scales and along different directions [1,2]. This can be simply deduced by considering the so-called “golden rule” for the transition probability between two quantum states. At first, one has to maximize the coupling matrix element between photons and electronic excitations; secondly, one has to enhance locally and in the appropriate spectral range the density of intermediate or final states. Taking the surface enhanced Raman spectroscopy as an example, the coupling reaches its maximum value in resonant conditions (SERRS) [3], thus defining the appropriate energy range of the incident and scattered photons. Moreover the enhancement can be considerably increased by exploiting the appropriate spatial localization through bi-layer interference enhanced Raman spectroscopy (BIERS) [4]. The spatial organization can be developed not only in the plane of the substrate (XYpatterning) but also in the direction perpendicular to the substrate (Z-patterning). On one hand, the geometrical parameters (grating spacing and layer thicknesses respectively) have to be adapted to the wavelength of the incoming and out coming photons. On the other hand, this wavelength can be fruitfully adapted to the plasmon oscillation in the metallic antenna and/or to the appropriate electronic transition in the nano-object under investigation. The strongest limitation for a widespread and routine use of plasmonic substrates is due to the drastic requirement of designing in a reproducible way, well defined nanoscale gaps between metallic structures. This is necessary for both mechanisms generally invoked for SERS: the so-called “electromagnetic” or “chemical” ones [3]. In this context it is particularly interesting to develop novel approaches for controlling the geometry at the sub-micron scale but also at the nanoscale. They will offer new opportunities for the design of optoe

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