Ultrasmooth silver thin film on PEDOT:PSS nucleation layer for extended surface plasmon propagation.

Poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) layers are used as the nucleation (seed) layer to reduce surface roughness of the overlying silver (Ag). The technique leads to ultrasmooth Ag thin films with a minimum surface roughness of 0.8 nm. The mechanism contributing to the improvement is explained on the basis of better wetting of Ag on PEDOT:PSS, and properties of the nucleation layer on the aspects of surface energy, surface adhesive force, and surface morphology influencing Ag wetting and growth pattern are being discussed. The surface plasmon resonance (SPR) shows significant improvement, in terms of the Figure of Merits (FOM), as the surface roughness on Ag films is reduced. A lower light scattering and longer plasmon propagation of maximum 15.3 μm are also realized on a smoother Ag surface. The results indicate great potential on the application of combined PEDOT:PSS/Ag structure as an effective and economically feasible design solution for plasmonic and optical metamaterials devices.