Ultrasensitive and Stable Plasmonic Surface-Enhanced Raman Scattering Substrates Covered with Atomically Thin Monolayers: Effect of the Insulating Property.

We demonstrated the effects of monolayer graphene and hexagonal boron nitride (h-BN) on the stability and detection performance of two types of substrates in surface-enhanced Raman scattering (SERS): a two-dimensional (2D) monolayer/Ag nanoparticle (NP) substrate and a Au NP/2D monolayer/Ag NP substrate. Graphene and h-BN, which have different electrical and chemical properties, were introduced in close contact with the metal NPs and had distinctly different effects on the plasmonic near-field interactions between metal NPs in the subnanometer-scale gap and on the electron transport behavior. A quantitative comparison was possible due to reproducible SERS signals across the entire substrates prepared by simple and inexpensive fabrication methods. The hybrid platform, an insulating h-BN monolayer covering the Ag NP substrate, ensured the long-term oxidative stability for over 80 days, which was superior to the stability achieved using conducting graphene. Additionally, a sandwich structure using an h-BN monolayer exhibited excellent SERS sensitivity with a detection limit for rhodamine 6G as low as 10-12 M; to the best of our knowledge, this is the best SERS detection limit achieved using monolayer h-BN as a gap-control material. In this study, we suggest an efficient strategy for hybridizing the desired 2D layers with metal nanostructures for SERS applications, where the substrate stability and electromagnetic field enhancement are particularly crucial for the various applications that utilize metal/2D hybrid structures.