Coherent plasmon coupling in spherical metallodielectric multilayer nanoresonators
Rohde, Charles Alan, 1977-
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Rohde, Charles Alan, 1977-
In this thesis we theoretically and experimentally investigate the subwavelength manipulation of light with nano-scale patterned metallodielectric resonators. By coupling light to surface plasmon excitations, we calculate the modified dispersion relation of the resulting surface plasmon polariton (SPP) modes in two types of subwavelength resonators: (i) closed, spherical micro-resonators with nano-scale metal-dielectic-metal shells; (ii) periodic, metal-dielectric-metal-layered silica surfaces. We show theoretically that with the proper geometric parameters, one can use sub-wavelength structure on spherical surfaces to manipulate the SPP dispersion relation in a highly tunable fashion. A tunable avoided-crossing of plasmonic dispersion bands is found to be the result of the coherent near-field coupling of silver nano-shell SPP modes. By developing our own stable computational algorithms, we calculated the far-field scattering of these metal-dielectric-metal layered micro-resonators. We demonstrate that the near-field interaction of the SPPs leads to a tunable, SPP induced transparency in the composite particle's scattering and extinction cross-sections. Utilizing finite element calculations, periodically-modulated metal-dielectric-metal layers are shown to alter the transmission properties of plasmon enhanced transmission through their support of interior surface plasmon (ISP) modes. Our simulations indicate that, subwavelength silver-silica-silver trilayers coating arrays of silica cylinders support ISP modes analogous to those found in spherical metal-dielectric-metal shells. We examine the coupling between ISP and radiating SPPs, and find the possibility of efficient free-space coupling to ISP modes in planar geometries. Further, the excitation of these ISP modes is found to predicate plasmon enhanced transmission, adding directionality and refined frequency selection. Experimentally, we show that self-assembled monolayers of silica spheres form a novel substrate for tunable plasmonic surfaces. We have developed a deposition method to conformally coat these hexagonal-close-packed substrates with nano-scale silver-polystyrene-silver coatings. We use angle-resolved spectroscopy to study their transmission properties. We have discovered that the presence of the silver-polystyrene-silver layer supports the excitation of ISP modes, and that these excitations significantly alter the plasmon enhanced transmission. Finally, we have discovered that the use of the ordered monolayers as a plasmonic substrate can create a new effect in conjunction with plasmon enhanced transmission: directionally asymmetric transmission. This is demonstrated with optically thick silver coatings evaporated upon onto the ordered sphere monolayers.