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Surface Enhanced Raman Spectroscopy (SERS) allows the intensity of Raman scattering to be enhanced by a factor of 10 6 by placing molecules within a few nm of a rough metal surface. In this paper we continue our investigation into a completely different configuration for a SERS sensor platform, incorporating an optical waveguide beneath a nanostructured precious metal coated surface. The nanostructured 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 should provide ideal parameters for maximum Raman interactions. Using Finite Difference Time Domain (FDTD) modelling methods the waveguide coupled SERS nanostructures were fully analyzed and their theoretical performance simulated by using frequency domain power monitors around the nanostructures. The model investigates efficiency of coupling between the waveguide and surface plasmons, but also investigates spatial localization around sharp features of the geometry. Simulations were completed using different types of etched nanostructures (pyramidal, circular, square) and dimensions to determine a suitable sensor area which would allow for maximum field intensity within the features when excited from underneath. The simulations suggested that a pitch of 2500nm, a circular feature length of 500nm and an etch depth of 400nm showed more field intensity within the nanostructured pits. |
