Gold-coated polystyrene bead array and the investigation of their plasmon coupling abilities

Many of SERS nanoparticles took advantage of the surface roughness for the significant improvement of their Raman sensing ability. Nevertheless, few papers analyzed the characteristics of surface roughness nanostructures that contribute to the SERS. Thus, this paper investigates the characteristics of the corrugated polystyrene bead (PSB) array etched by a series of oxygen plasma etching time for giving a criterion to fabricate appropriate SERS-active nanoparticles. Three factors were considered in this paper: (1) the effect of plasma coupling among neighboring particles, (2) the vertical surface roughness of nanocorrugations, and (3) the pitch size, the lateral surface roughness, of nanocorrugations. By the analysis of SEM and AFM images, those factors were quantifiable. The correlation coefficient between each factor and SERS Raman enhancement was also investigated to verify that the pitch size of nanocorrugations (ranging from ~6 nm to ~12 nm on the surface of PSBs) dominates the SERS enhancement. Therefore, the maximum improvement of Raman intensity that derives from surface roughness treatment is 12 times compared to smooth surface. Moreover, it has a high enhancement factor of ~10⁶.