FDTD Simulations of Nanopost Plasmonic Crystals for SERS

Alec Bigness and Jason M. Montgomery

Department of Chemistry, Biochemistry, and Physics
Florida Southern College, Lakeland, FL 33801

We present results for the theoretical modeling of nanopost plasmonic crystals (NPCs) as effective surface enhanced Raman spectroscopy (SERS) substrates. NPCs are composed of arrays of dielectric posts (with cylindrical or rectangular cross-sections), upon which thin layers of gold are deposited. This gives rise to a plasmonic gold film and nanopost discs that can couple to yield high electric field enhancements of incident light at a surface plasmon resonance. These resonances can be tuned via variations in size, shape, height, and periodicity of the NPCs. Using the finite-difference time-domain (FDTD) method, we calculated the average electric field intensities at both excitation and emission wavelengths to calculate a SERS response for a number of nanopost arrays. Results were compared with experimental measurements from a separate study to validate the FDTD method. NPCs were then optimized for SERS by varying the NPC geometries: size, shape, height, aspect ratio, and periodicity. The best geometries were those that coupled local surface plasmon resonances of the discs with Bloch-wave surface plasmon polaritons excited on the film.