Spacer layer effect in fluorescence enhancement from silver nanowires over a silver film; switching of optimum polarization.

We explore the role of coupling between silver nanowires and an underlying silver film in fluorescence enhancement from proximal molecules. Variation of the thickness of an oxide layer separating nanowire arrays from the Ag film causes an alternation in the incident light polarization that produces the highest enhancement. Finite difference time domain calculations show that it results from an alternation of regions of high field above and between nanowires as the spacer thickness is increased.