Integration of nanostructures and waveguide core for surface enhanced Raman spectroscopy: a novel excitation method

Pearce, S., Charlton, M.D.B., Pollard, M., Oo, Swe Zin and Chen, R. (2012) Integration of nanostructures and waveguide core for surface enhanced Raman spectroscopy: a novel excitation method. Photonics West 2012, , San Francisco, United States. 21 - 26 Jan 2012. (doi:10.1117/12.910476).

Abstract

Surface Enhanced Raman Spectroscopy (SERS) allows the intensity of Raman scattering to be enhanced by a factor of 10⁶ by placing molecules within a few nm of a rough metal surface. In this paper we investigate a completely different configuration for the excitation mechanism, incorporating an optical waveguide beneath a nano-structured precious metal surface. The pyramidal geometry projects the Plasmon field into free space, thus increasing the cross section of interaction between the analyte molecules and optical fields, thereby increasing device sensitivity. In this arrangement the excitation field comes from underneath and enters the nanostructures at the base. This allows the emission to reach the discrete sensing areas effectively and provides ideal parameters for maximum Raman interactions. Using FDTD modeling methods the waveguide coupled SERS nanostructures were analyzed and its performance at different gold thicknesses was determined. The model investigates efficiency of coupling between the waveguide and surface plasmons, but also investigates spatial localization around sharp features of the geometry. Thin films of aluminum oxide and silicon oxynitride were reactively sputtered and characterized to determine their suitability as the waveguide core material. It was found that silicon oxynitride slab waveguide losses were too high to be considered as the core. The 2D and 3D simulations were based on an aluminum oxide core.

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