FEM Analysis and Application of Surface-Enhanced Raman Scattering (SERS) Nanostructure Substrate for Optical PH Sensor

The design and fabrication of a SERS pixel array is presented, whose purpose is to provide spatially resolved measurement of chemical PH in a fluid. Ultimately the goal is to provide real-time monitoring of a chemical reaction.

The pixels are consist of a nanostructure substrate composed of an array of projections or cavities. The shape of the nanostructures and the thickness of the metallic (Ag or Au) layer can be tuned to give maximal enhancement at the desired wavelength. The number and arrangement of nanostructures was optimized to obtain maximal responsivity.

Analytical and numerical methods were used to model Surface Enhanced Raman Scattering. The primary numerical tool was FEM analysis using COMSOL combined with algorithmic optimization algorithms such a Simulated Annealing and Method of Simplexes.

The enhancement of Raman emission from emitters which are volume-dispersed in a fluid, as well as the posibility of near-field, detection through plasmonic antennae required the development of novel simulation approaches which go beyond the current approach based on surface-averages in the E⁴ approximation. Methods of numerically simulating incoherent radiation, using a Monte-Carlo approach for individual source phases, and a new continuum model were investigated.