Highly uniform plasmonic microstructures for surface-enhanced Raman scattering applications

Plasmonic microstructures have potential applications for surface-enhanced Raman scattering. Consistent microstructure features are crucial to ensure spatial reliability and accuracy of measurements. In this work, we assessed the performance of surface-enhanced Raman scattering using plasmonic self-assembled microstructures. The plasmonic microstructures were prepared from polystyrene beads with 500-nm and 1000-nm diameters via convective deposition and capped by sputtering a thin gold film. Raman scattering spectra of the probe molecule methylene blue were measured at a 785 nm excitation wavelength. Enhancement factors of 7.8×105 and 3.9×106 were obtained for 500-nm and 1000-nm plasmonic microstructures, respectively. The higher enhancement factor for the 1000-nm microstructure case is attributed to strong electric field near the semi-shell surface and near-field localization above the structure. The uniformity of the surface-enhanced Raman scattering substrates was evaluated by comparing the Raman shift intensities at 1610 cm-1 at 20 distinct locations on each substrate. The relative standard deviations (RSD) were found to be 0.032% and 0.018% for 500-nm and 1000-nm templates, respectively. These plasmonic microstructures can be useful for surface-enhanced Raman scattering applications.