Gap-free hybridized plasmonics with tunable decay channels for surface-enhanced Raman spectroscopy

Surface-enhanced Raman spectroscopy (SERS) has been applied in many analytical fields owing to its features like single molecule sensitivity and fingerprint identification. To face the challenges in detecting large molecules, developing gap-free SERS substrates with excellent performance as well as desired electromagnetic (EM) field distribution is receiving increasing attentions. Herein, we propose a highly uniform gap-free SERS substrate consisting of Au nanodisk array / Si nanopillar spacer / Au nanohole array. The mode-hybridization between optical cavity mode and SPR mode can be simply and effectively controlled by tuning the cavity height, then the enhanced EM field can be optimized to the top surface, which is more available for analytes. Simultaneously, the decay channels were also manipulated to reduce the heat effect (with a decrease of around 10℃) of non-radiative decay during SERS measurement. Such a SERS substrate shows a great performance with the average enhancement factor of 6×10⁶ as well as a high uniformity (with a relative standard deviation of 8.5 %). This work provides new opportunities for the design and applications of gap-free SERS substrates.