Highly reproducible and stable surface-enhanced Raman scattering substrates of graphene-Ag nanohole arrays fabricated by sub-diffraction plasmonic lithography

Abstract

Surface-enhanced Raman scattering (SERS) has shown great promise for trace detection due to its high sensitivity. The lack of efficient fabrication methods for large-scale SERS substrates with high sensitivity, high reproducibility, and stability has greatly limited the development of practical SERS sensing devices. In this work, we report sub-diffraction, high throughput, and low-cost fabrication of SERS substrates with plasmonic cavity lens (PCL) lithography. The PCL is a photoresist layer sandwiched with two Ag layers, which could greatly improve the lithographic resolution and fidelity. Ag nanohole arrays (AgNHs) over a 5 × 5 mm2 area were fabricated onto the bottom Ag reflective layer, which worked as SERS substrates. The SERS substrates exhibited enhancement factors (EFs) of 107 that are capable of monolayer detection. The reproducibility is less than 9%, which is much better than that of substrates synthesized with traditional chemical methods. The graphene (GE) layer was transferred onto AgNHs to increase the SERS stability, as demonstrated with only a 25.8% decrease of SERS intensity for 90 day exposure to air and a 78.3% decrease for the control case without GE. This work has demonstrated that PCL lithography technique is a promising method for fabrication of SERS substrates with large-area, high sensitivity, high reproducibility, and low-cost.