19 September 2013 Waveguide core integrated nanostructured SERS sensor platform
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Abstract
The intensity of Raman scattering can be enhanced by a factor of 106 using Surface Enhanced Raman Spectroscopy (SERS). In this method, molecules are placed within a few nm of a rough/nanostructured metal surface. In this paper we show fabrication and characterisation of an integrated optical waveguide beneath a nano-structured precious metal coated surface. By using a waveguide core, 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. 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. Thin films of silicon oxynitride were deposited using PECVD on to thermal oxide coated 4 inch wafers and annealed at various temperatures to obtain low loss layers suitable for the waveguide core material. Based on the results from our simulations, nanostructured features of various diameters/feature lengths and pitch were etched into the low loss silicon oxynitride layer. The sensor area was coated with a thin layer of gold (25nm) and a variety of optical measurements were completed for many of the processed test chips including broadband reflectrometry, normal incident Raman spectroscopy and waveguide Raman spectroscopy using a Raman probe above the sensor area. The results showed that detection of a Raman active molecule (Benzyl Mercaptan) was possible when excited from the underlying waveguide core with 104 sensitivity.
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S. J. Pearce, S. J. Pearce, S. Oo, S. Oo, M. E. Pollard, M. E. Pollard, R. Chen, R. Chen, S. Kalsi, S. Kalsi, M. D. B. Charlton, M. D. B. Charlton, "Waveguide core integrated nanostructured SERS sensor platform", Proc. SPIE 8818, Nanostructured Thin Films VI, 88180F (19 September 2013); doi: 10.1117/12.2022208; https://doi.org/10.1117/12.2022208
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