Au/Ag bimetal nanogap arrays with tunable morphologies for surface-enhanced Raman scattering

When Au and Ag were deposited onto two-dimensional polystyrene (PS) templates, a curved bimetallic film composed of nanocap-shaped Au/Ag units was formed. The "Y"-shaped nanogaps and "V"-shaped junctions were tailored between the neighbour nanocaps by changing the bilayer thickness and PS diameters. Compared to the curved Ag, the curved Au monolayer and the flat Au/Ag bilayer on a silicon wafer, the curved Au/Ag bimetallic film exhibited significant SERS enhancement, which was mainly attributed to two important factors, the nanogaps between the adjacent Au/Ag nanocaps and the composite of the Ag/Au bimetallic film. And the nanogaps generated extremely intense local electromagnetic fields and the composite provided more possibilities for the residence of probing molecules.