Ultrasensitive molecular sensing of few-layer niobium diselenide

Abstract

Developing non-noble-metal-based materials with an excellent surface-enhanced Raman scattering (SERS) effect is indispensable for cost-effective, fast and nondestructive detection of trace amounts of molecules. Two-dimensional metallic transition metal dichalcogenides (TMDCs) are emerging in SERS fields by virtue of their ultra-flat atomic surface, high surface activity and abundant density of states (DOS) near the Fermi level. However, how to further decrease the limits of detection of TMDCs substrates is crucial but very challenging. In this contribution, large-area NbSe₂ flakes from monolayer to few-layer are controllably synthesized via an ambient pressure chemical vapor deposition route. The ultrasensitive SERS effect of NbSe₂ is demonstrated by optimizing the layer-dependent structure–effect correlation both experimentally and theoretically. As a proof of concept, Rhodamine 6G (R6G) molecules with an ultralow concentration of 5 × 10⁻¹⁶ M can be detected on 6L-NbSe₂, which is five orders of magnitude lower than that on 1L-NbSe₂. The ultrasensitive SERS effect of few-layer NbSe₂ is attributed to the strong adsorption energy and efficient charge transfer between R6G and NbSe₂ with specific layers induced by the highest DOS at the Fermi level. Our study provides new insight into the molecular sensing research of 2D TMDCs and paves the way for designing ultrasensitive SERS substrates.