Nanostructured metal films comprised of periodically arranged spherical voids are grown by electrochemical deposition through a self-assembled template. Detailed measurements of the angle-and orientation-dependent reflectivity for different sample geometries reveal the spectral dispersion of several different types of surface plasmon modes. The dependence of the energies of both delocalized Bragg and localized Mie plasmons on the void goemetry is presented, along with theoretical models to explain some of these experimental findings. Strong interactions between the different plasmon modes as well as other mixing processes are identified. Understanding such plasmonic crystals allows for the engineering of devices tailored for a wide range of sensing application.

Metallic nanoscale voids ("anti-nanoparticles") are shown to possess radically different plasmon modes to metal nanoparticles. Comparing new boundary element calculations for the first time with experiment clearly and intuitively identifies plasmon wavefunctions in spherical voids according to their atomic-like symmetries. As the spherical voids are progressively truncated, the degenerate radial modes split in energy, with intense coupling to incident light at specific optimal angles. In contrast to nanoparticles, voids embedded in metal films possess additional rim plasmon modes that selectively couple with void plasmons to produce bonding and antibonding hybridized states with significant field enhancements. These modes, which are verified in experiment, are crucial for the effective use of plasmons in antenna applications such as reproducible surface enhanced Raman scattering.

Even 35 years after the discovery of surface-enhanced Raman spectroscopy (SERS) much remains to be learned about the phenomenon.1-3 Despite broad consensus on the mechanism of SERS, many features remain poorly understood and in particular much less effort has been put into understanding the continuum emission called the "background" observed in SERS spectra. Here the SERS background is studied systematically on sphere segment void (SSV) plasmonic substrates. We establish the physicochemical dependence of the background on plasmons, the identity of the adsorbate, adsorbate coverage and electrochemical potential. In particular, by exchanging electron-donating and electron-withdrawing adsorbates, we demonstrate predictable modulation of the SERS background. Using these observations, we propose a model for the origin of the SERS background. Finally, we test the proposed model against its predictions for anti-Stokes SERS spectra.

Colloidal-crystal templated electrodeposition can be used to fabricate sphere segment void (SSV) substrates that show large, reproducible enhancements in surface-enhanced Raman spectroscopy (SERS). These SSV substrates support a variety of plasmon modes and can be fully characterized by white light dispersion measurements allowing the direct identification of the modes predicted by computational models of the nanoscale optical fields. Comparing plasmon absorption with SERS enhancements as a function of sphere segment void diameter and metal thickness for a series of SSV substrates allows the identification of the specific plasmon modes, which give rise to large SERS enhancements at different laser wavelengths and in different media. The measured SERS intensities show direct correlation to the plasmonic modes of the structures providing a guide to the design of efficient surfaces for SERS.

A new self-aligned robust method for coupling to whispering gallery modes (WGMs) of submicron microspheres utilizes their periodic arrangement without relying on nanopositioned external coupling devices. The microspheres are embedded in a nanostructured gold surface supporting delocalized plasmonic crystal modes that mediate the coupling, and can be tuned by the geometry. Detailed measurements of the angle-and orientation-dependent reflectivity reveal localized plasmonic WGMs whose energies scale with sphere diameter and agree closely with Mie calculations. Coupling between these plasmonic WGMs leads to mode splitting and the formation of plasmonic minibands of a controllable bandwidth. DOI: 10.1103/PhysRevLett.97.137401 PACS numbers: 78.67.Bf, 42.70.Qs, 73.20.Mf, 81.07.ÿb Microspheres form one of the key elements in nanophotonic devices due to the tight confinement and strong enhancement of the optical field. However, coupling into microspheres is difficult due to the weak exponentially decaying evanescent external field, and has been demonstrated only with nanopositioned elements such as prisms [1,2], modified optical fiber probes (using tapers [3], etcheroded [4] or angle-polished [5] fiber tips, half-block fiber couplers), or planar waveguides [6]. These methods require precise nanometer control in the optical near field, placing tight tolerance on alignment and fabrication. Current whispering gallery mode (WGM) research has tended to focus on large dielectric microspheres (from several to hundreds of microns) with high Q factors and which support many closely spaced modes of very narrow linewidth. This mode quasidegeneracy and the large size restricts applications, for instance, in coupling to small numbers of nanoemitters. Additionally, microspheres are frequently supported on flat or grooved substrates, with the outer surface in air or liquid, providing limited scope for control of interactions. Because of the difficulty of matched coupling, most studies collect photoluminescence (PL) from dye-doped spheres in which small numbers of spheres can be resolved although the excitation conditions are not well controlled [7][8][9].Here we demonstrate for the first time strong WGM resonances in embedded spheres with submicron diameters. Since the sphere dimensions (diameters d 0:4 to 1 m) are comparable to the wavelength of illuminating light we observe the lowest order WGM modes directly. These modes can be observed in reflectivity through the entire visible and IR spectral ranges and are conveniently widely spaced energetically. By using a far-field resonant coupling method only possible for such embedded microspheres in a metal film, we can study the full angular dependence of these modes and observe the mode linewidths and absorption depths directly as the film thickness is varied. The observed localized modes combine aspects of both WGMs and void plasmons [10,11] as their angular mode index, l, changes and hence are termed plasmonic WGMs below. We clearly resolve the evolution from delocalized surface pl...

Graphene mechanical resonators have recently attracted considerable attention for use in precision force-and mass-sensing applications. To date, readout of their oscillatory motion typically requires cryogenic conditions to achieve high sensitivity, restricting their range of applications. Here we report the demonstration of an evanescent optical readout of graphene motion, using a scheme which does not require cryogenic conditions and exhibits enhanced sensitivity and bandwidth at room temperature. We utilize a high-Q microsphere to enable the evanescent readout of a 70-μm-diameter graphene drum resonator with a signal-to-noise ratio of greater than 25 dB, corresponding to a transduction sensitivity of S 1=2 N ¼ 2.6 × 10 −13 m Hz −1=2 . The sensitivity of force measurements using this resonator is limited by the thermal noise driving the resonator, corresponding to a force sensitivity of F min ¼ 1.5 × 10 −16 N Hz −1=2 with a bandwidth of 35 kHz at room temperature (T ¼ 300 K). Measurements on a 30-μm graphene drum have sufficient sensitivity to resolve the lowest three thermally driven mechanical resonances. The graphene drums couple both dispersively and dissipatively to the optical field with coupling coefficients of G=2π ¼ 0.21 MHz=nm and Γ dp =2π ¼ 0.1 MHz=nm, respectively.

Iridium oxide electrodeposited through a self-assembled colloidal template has an inverse opal structure. Monolayers present long range hexagonal arrangements of hemispherical nanocavities while multilayers present 3D honeycomb structures with spherical voids. The films are amorphous, 10 have several electroactive redox states and are electrochromic. The nanostructure modifies their reflectivity thus indicating these films could be used as tunable photonic devices.

Ultraviolet laser excited surface-enhanced Raman scattering was obtained for the first time at the well ordered palladium sphere segment void (SSV) nanostructures, using adenine as the probe molecule, and the UV-SERS enhancement is found to be correlated well with the plasmon absorption of Pd SSVs in the UV region.