Electrically Tunable Quasi-3-D Mushroom Plasmonic Crystal

This paper reports an electrically tunable plasmonic crystal incorporating a nematic liquid crystal (LC) layer on the top surface of quasi-3-D mushroom plasmonic nanostructures. The presented plasmonic crystal is formed by an array of polymeric mushroom nanoposts with gold disks at the top and perforated nanoholes in a gold thin film at the bottom. The coupling between surface plasmon polariton (SPP) and Rayleigh anomaly (RA) is observed in experiments with quasi-3-D plasmonic crystals, and verified by simulations. The coupled SPP-RA resonance mode has its electric field vector prominently normal to the surface of the plasmonic nanostructures, and extends into the surrounding medium. This feature makes the coupled resonance sensitive to molecular reorientation in LC, and thus, is useful for designing index modulation-based tunable plasmonic crystal devices. Therefore, by applying external voltages across the LC layer, the SPP-RA resonance mode shows a redshift of 8 nm with a 35% change in the amplitude.