Controlled Topography Change of Subdiffraction Structures Based on Photosensitive Polymer Films Induced by Surface Plasmon Polaritons

We discuss the controlled subdiffraction modulations of photosensitive polymer films that are induced by surface plasmon interference in striking contrast to well-known conventional microscopic gratings. The near-field light intensity patterns were generated at the nanoslits fabricated in a silver layer with the photosensitive polymer film placed above. We observed that the topographical modulations can be excited only when the polarization is perpendicular to the nanoslits. Moreover, we have shown that light with certain wavelengths resulted in a characteristic topographical pattern with the periodicity three times smaller than the wavelength of incoming light. A combination of experimental observations with simulations showed that the unique subdiffraction topographical patterns are caused by constructive interference between two counter-propagating surface plasmon waves generated at neighboring nanoslits in the metal layer beneath the photosensitive polymer film. The light intensity distribution was simulated to demonstrate strong dependency upon the slit array periodicity as well as wavelength and polarization of incoming light

Stacked Gold Nanorectangles with Higher Order Plasmonic Modes and Top-Down Plasmonic Coupling

We present stacked hollow nanostructures created using electron beam lithography (EBL) that act as optical scattering sites with a complex combination of local surface plasmon resonances and top-down electromagnetic hotspots due to the incorporation of the third dimension into their construction. These hollow rectangular gold nanotructures with gold caps show a significant red-shift in their main scattering peak as compared to the solid structures. Finite-difference time-domain modeling shows that the plasmonic response of these structures is dominated by higher order plasmonic modes and that the strength of these modes is shown to vary according to whether a cap is present. The higher order dipolar mode caused by the capped nanostructure results in manifold increase in the intensity of the electric field compared to the quadrupolar mode from a solid rectangle. This analysis provides important information on how complex plasmonic resonances respond to structural changes which will be useful in future studies that utilize these coupled resonances for detection or light manipulation. In addition, the stacking scheme presents a new route for modifying the optical response of plasmonic nanostructures through top-down plasmonic coupling which may yield plasmon resonance modes not observed in common 2D nanostructures along with significant increases in the local electric fields of these open “hotspots”