Synergistic SERS Enhancement in Ag NW/WSe2 Heterostructures: Interfacial Charge Transfer and Layer-Dependent Sensitivity

Surface-enhanced Raman scattering (SERS) substrates based on metal/two-dimensional (2D) semiconductor composites offer unique advantages, yet macroscopic ensemble platforms suffer from spatial nonuniformity that obscures interfacial mechanisms. A deterministic SERS platform was constructed by precisely integrating an individual Ag NW across silica–monolayer (1L) and monolayer–bilayer (2L) WSe2 boundaries. The Ag NW–1L WSe2 hybrid exhibits Raman intensities up to 7.4 times higher than Ag NWs on silica and 4.0–4.5 times higher than Ag NWs on 2L WSe2. Density functional theory calculations reveal that Ag donates ∼0.36 e to WSe2, while 1L WSe2 confines the transferred electrons to its surface, yielding a high surface charge density. In contrast, 2L WSe2 exhibits spatial charge delocalization across the bilayer, reducing the surface electron density. This work offers a controllable strategy to eliminate ensemble averaging and clarifies layer-dependent interfacial dynamics in metal–2D semiconductor heterostructures.