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Controlling the permittivity of materials enables control over the amplitude, phase and polarization of light interacting with them. Tailorable and tunable transparent conducting oxides have applications in optical switching, beam steering, imaging, sensing, and spectroscopy. In this work, we experimentally demonstrate wide tailoring and tuning of the optical properties of oxides to achieve fast switching with large modulation depths. In cadmium oxide, the permittivity and the epsilon-near-zero points can be tailored via yttrium doping to achieve large, ENZ-enhanced mid-IR reflectance modulation. In zinc oxide, the permittivity is tuned by interband pumping, achieving large reflectance modulation in the telecom regime. With aluminum-doped zinc oxide, we demonstrate tailorable Berreman-type absorbers that can achieve ultrafast switching in the telecom frequencies. Our work will pave the way to practical optical switching spanning the telecom to the mid-infrared wavelength regimes.

We demonstrate significant epsilon-near-zero point shifts (11.3 pm to 5.3 pm), extraordinarily large (135%) optically-induced reflection modulation with picosecond response times, and carrier relaxation time-engineering in cadmium oxide via Yttrium doping.

We experimentally demonstrate a metasurface that supports tailorable polaritons arising from strong coupling between Mie modes of dielectric nanoresonators and intersubband transitions of semiconductor quantum wells that are embedded inside the resonator.

It is well-known that a slotted resonant cavity with high-quality factor exhibits interior electromagnetic (EM) fields that may be even larger than the external field. The authors aim to reduce the cavity's EM fields and quality factor over a frequency band analytically, numerically, and experimentally by introducing microwave absorbing materials in the cavity. A perturbation model approach was developed to estimate the quality factor of loaded cavities, which is validated against full-wave simulations and experiments. Results with 78.7 mils (2 mm) thick ECCOSORB-MCS absorber placed on the inside cavity wall above and below the aperture slot (with only 0.026% cavity volume) result in a reduction of shielding effectiveness >19 dB and reductions in quality factor >91%, providing confirmation of the efficacy of this approach.

Epsilon-near-zero materials provide a new path for tailoring light-matter interactions at the nanoscale. In this paper, we analyze a compact electroabsorption modulator based on epsilon-near-zero confinement in transparent conducting oxide films. The nonresonant modulator operates through field-effect carrier density tuning. We compare the performance of modulators composed of two different conducting oxides, namely, indium oxide (In2O3 ) and cadmium oxide (CdO), and show that better modulation performance is achieved when using high-mobility (i.e., low loss) epsilon-near-zero materials such as CdO. In particular, we show that nonresonant electroabsorption modulators with submicron lengths and greater than 5 dB extinction ratios may be achieved through the proper selection of high-mobility transparent conducting oxides, opening a path for device miniaturization and increased modulation depth.

Metamaterials research has developed perfect absorbers from microwave to optical frequencies, mainly featuring planar metamaterials, also referred to as metasurfaces. In this study, we investigated vertically oriented metamaterials, which make use of the entire three-dimensional space, as a new avenue to widen the spectral absorption band in the infrared regime between 20 and 40 THz. Vertically oriented metamaterials, such as those simulated in this work, can be experimentally realized through membrane projection lithography, which allows a single unit cell to be decorated with multiple resonators by exploiting the vertical dimension. In particular, we analyzed the cases of a unit cell containing a single vertical split-ring resonator (VSRR), a single planar split-ring resonator (PSRR), and both a VSRR and PSRR to explore intra-cell coupling between resonators. We show that the additional degrees of freedom enabled by placing multiple resonators in a unit cell lead to novel ways of achieving omnidirectional super absorption. Our results provide an innovative approach for controlling and designing engineered nanostructures.

We demonstrate the ultrafast formation of terahertz (THz) metasurfaces through all-optical creation of spatially modulated carrier density profiles in a deep-subwavelength GaAs film. The switch-on of the transient plasmon mode, governed by the GaAs effective electron mass and electron–phonon interactions, is revealed by structured-optical pump THz probe spectroscopy, on a time scale of 500 fs. By modulating the carrier density using different pump fluences, we observe a wide tuning of the electric dipole resonance of the transient GaAs metasurface from 0.5 THz to 1.7 THz. Furthermore, we numerically demonstrate that the metasurface presented here can be generalized to more complex architectures for realizing functionalities such as perfect absorption, leading to a 30 dB modulation depth. The platform also provides a pathway to achieve ultrafast manipulation of infrared beams in the linear and, potentially, nonlinear regime.

Epsilon-near-zero (ENZ) modes provide a new path for tailoring light–matter interactions at the nanoscale. In this paper, we analyze a strongly coupled system at near-infrared frequencies comprising plasmonic metamaterial resonators and ENZ modes supported by degenerately doped semiconductor nanolayers. In strongly coupled systems that combine optical cavities and intersubband transitions, the polariton splitting (i.e., the ratio of Rabi frequency to bare cavity frequency) scales with the square root of the wavelength, thus favoring the long-wavelength regime. In contrast, we observe that the polariton splitting in ENZ/metamaterial resonator systems increases linearly with the thickness of the nanolayer supporting the ENZ modes. In this work, we employ an indium-tin-oxide nanolayer and observe a large experimental polariton splitting of approximately 30% in the near-infrared. This approach opens up many promising applications, including nonlinear optical components and tunable optical filters based on con...

Three-dimensional (3D) metafilms composed of periodic arrays containing single and multiple micrometer-scale vertical split ring resonators per unit cell were fabricated using membrane projection lithography. In contrast to planar and stacked planar structures such as cut wire pairs and fishnet structures, these 3D metafilms have a thickness t ~λd/4, allowing for classical thin film effects in the long wavelength limit. The infrared specular far-field scattering response was measured for metafilms containing one and two resonators per unit cell, and compared to numerical simulations. Excellent agreement in the frequency region below the onset of diffractive scattering was obtained. The metafilms demonstrate strong bi-anisotropic polarization dependence. Further, we show that for 3D metafilms, just as in solids, complex unit cells with multiple atoms (inclusions) per unit cell possess a richer set of excitation mechanisms. The highlight of these new coupling mechanisms is the excitation of the 3D analog to the 2D cut-wire-pair magnetic response.

Coupling of metasurfaces to intersubband transitions (ISTs) in semiconductor quantum wells (QWs) has been extensively studied for various applications ranging from generating giant nonlinear optical response to designing tunable metasurfaces for applications such as ultrafast spatial optical modulators and voltage tunable filters. In this work, we experimentally demonstrate a fundamentally new approach of actively controlling the coupling of ISTs in QWs to a metasurface for voltage tuning its optical response. Unlike previous approaches, we use voltage-controlled quantum tunneling to control the carrier concentration in the QWs for turning on/off the ISTs. We design a multi-quantum well structure consisting of four undoped InGaAs wells with AlInAs barriers grown on top of a highly doped InGaAs layer that acts as an electron reservoir. The heterostructure is optimized such that the first IST in all the wells is at 11µm. A complementary gold metasurface with dipole resonances at 11µm is fabricated on top of the QW structure. We designed the heterostructure such that by applying a bias of 1V, the energy bands of all the QWs get aligned simultaneously, leading to the occupation of the ground state of all the QWs via quantum tunneling of the electrons from the electron reservoir. The ISTs which were turned off due to negligible electron density gets turned on at 1V, and this leads to coupling between the ISTs and the dipoles resonances of the metasurface. The voltage induced coupling leads to reflectance modulation which we confirmed experimentally by rapid scan double modulation FTIR measurements.

Metasurfaces have been investigated for various applications ranging from beam steering, focusing, to polarization conversion. Along with passive metasurfaces, significant efforts are also being made to design metasurfaces with tunable optical response. Among various approaches, voltage tuning is of particular interest because it creates the possibility of integration with electronics. In this work, we demonstrate voltage tuning of reflectance from a complementary metasurface strongly coupled to an epsilon-near-zero (ENZ) mode in an ultrathin semiconductor layer. Our approach involves electrically controlling the carrier concentration of the ENZ layer to modulate the polaritonic coupling between the dipole resonances of the metasurface and the ENZ mode for modulating the reflectance of the metasurface. The hybrid structure we fabricate is similar to MOSCAP configuration where the complementary metasurface offers a continuous gold top layer for biasing and positive/negative bias to the metasurface leads to accumulation/depletion of carriers in the ENZ layer beneath it. We optimized our structure by using InGaAs as the ENZ material because of its high mobility and low effective mass. This allowed us to reduce the doping requirement and thereby reduce the ionized impurity scattering as well as the reverse bias required to deplete the ENZ layer. For low leakage and efficient modulation of carrier density, we used Hafnia as the gate dielectric. We further added a reflecting backplane below the ENZ layer to enhance the interaction and by applying bias, we achieved spectral shifts of 500 nm and amplitude modulation of 11% of one of the polariton branches at 14 µm.

In this paper, we analyze a compact silicon photonic phase modulator at 1.55 μm using epsilon-near-zero transparent conducting oxide (TCO) films. The operating principle of the non-resonant phase modulator is field-effect carrier density modulation in a thin TCO film deposited on top of a passive silicon waveguide with a CMOS-compatible fabrication process. We compare phase modulator performance using both indium oxide (In2O3) and cadmium oxide (CdO) TCO materials. Our findings show that practical phase modulation can be achieved only when using high-mobility (i.e. low-loss) epsilon-near-zero materials such as CdO. The CdO-based phase modulator has a figure of merit of 17.1°/dB in a compact 5 μm length. This figure of merit can be increased further through the proper selection of high-mobility TCOs, opening a path for device miniaturization and increased phase shifts.

We demonstrate thinned resonant longwave infrared detectors with quantum efficiencies of over 60% in the longwave infrared. This improvement over unthinned detectors is made possible by a nanoantenna that confines the incident optical energy in a reduced volume compared to traditional detector architectures.

We experimentally demonstrate a novel approach of using coupling between a leaky mode resonance and intersubband transitions in semiconductor quantum wells to realize a hybrid dielectric-semiconductor metasurface with high second-harmonic conversion efficiency and increased bandwidth.

We experimentally demonstrate spectral tuning and amplitude modulation of reflectance at long infrared wavelengths using a complementary metasurface strongly coupled to an epsilon-near-zero (ENZ) mode in an ultrathin InGaAs layer with a reflecting backplane.

We demonstrate active tuning of high-Q dielectric metasurfaces by embedding asymmetric silicon meta-atoms in liquid crystals, thus controlling the relative refractive index by heating. Spectral tuning of more than three resonance widths is achieved.

The noise performance of infrared detectors can be improved through utilization of thinner detector layers which reduces thermal and generation-recombination noise currents. However, some infrared detector materials suffer from weak optical absorption and thinning the detector layer can lead to incomplete absorption of the incoming infrared photons which reduces detector quantum efficiency. Here, we show how subwavelength metallic nanoantennas can be used to boost the efficiency of photon absorption for thin detector layers, thereby achieving overall enhanced detector performance.

We examine integration of a patterned metal nanoantenna (or metasurface) directly onto long-wave infrared detectors. These structures show significantly improved external quantum efficiency compared to their traditional counterparts. We will show simulation and experimental results.

Using a high-electron-mobility cadmium oxide perfect absorber and intraband optical pumping, we experimentally demonstrate a reflective polarizer with a polarization extinction ratio of 91 that can be switched on and off within 800 fs.

We demonstrate high-speed operation of ultracompact electroabsorption modulators based on epsilon-near-zero confinement in indium oxide (In 2 O 3 ) on silicon using field-effect carrier density tuning. Additionally, we discuss strategies to enhance modulator performance and reduce confinement-related losses by introducing high-mobility conducting oxides such as cadmium oxide (CdO).

We study optically-excited nonlocalities in thin films of doped cadmium oxide. Although these effects are usually weak and hardly observable in the optical response of noble metals, the free-electron nonlocality is significantly increased in doped-cadmium-oside thin films. This increase is due mainly to: (i) low electron scattering rates; and (ii) interband transitions due to valence-band and inner-core electrons that occur far from the epsilon-near-zero frequency. The optical nonlocality manifests itself in the blueshift of the epsilon-near-zero mode, an associated reflectance dip, and the onset of higher-order modes. We model the structure using a generalized hydrodynamic theory that treats the free electrons in the film as a viscoelastic fluid. We demonstrate that both elasticity and viscosity play a significant role in the optical response of the film. The elasticity induces optical resonances associated with the longitudinal pressure modes of the free-electrons fluid, leading to a thickness-dependent permittivity. The viscosity introduces nonlocal damping and additional losses. In our view, this demonstration furthers our understanding of the dynamics of light-matter interactions, and adds a significant stepping stone toward the ability to effectively manipulate linear and nonlinear optical properties at the nanoscale.

We experimentally demonstrate high-contrast, ultrafast switching of infrared light at 2.1 μm via intraband pumping of a high quality factor perfect absorber made from a highly doped cadmium oxide thin film.

We demonstrate the active tuning of all-dielectric metasurfaces exhibiting high-quality factor (high-Q) resonances. The active control is provided by embedding the asymmetric silicon meta-atoms with liquid crystals, which allows the relative index of refraction to be controlled through heating. It is found that high quality factor resonances ($Q=270\pm30$) can be tuned over more than three resonance widths. Our results demonstrate the feasibility of using all-dielectric metasurfaces to construct tunable narrow-band filters., Comment: 4 pages, 6 figures

We report the first high-speed demonstration of a compact electroabsorption modulator based on epsilon-near-zero confinement in conducting oxide films. The non-resonant, 4μm-long device operates simultaneously over the entire C band through field-effect carrier density tuning.

We study the role of carrier mobility in transparent conducting oxides integrated into epsilon-near-zero modulators. High-mobility materials including CdO enable sub-micron length electroabsorption modulators through >4dB/µm extinction ratios.

We present the design, realization, and characterization of optical strong light–matter coupling between intersubband transitions within a semiconductor heterostructures and planar metamaterials in the near-infrared spectral range. The strong light–matter coupling entity consists of a III-nitride intersubband superlattice heterostructure, providing a two-level system with a transition energy of ∼0.8 eV (λ ∼1.55 μm) and a planar “dogbone” metamaterial structure. As the bare metamaterial resonance frequency is varied across the intersubband resonance, a clear anticrossing behavior is observed in the frequency domain. This strongly coupled entity could enable the realization of electrically tunable optical filters, a new class of efficient nonlinear optical materials, or intersubband-based light-emitting diodes.

We investigate optical polariton modes supported by subwavelength-thick degenerately doped semiconductor nanolayers (e.g. indium tin oxide) on glass in the epsilon-near-zero (ENZ) regime. The dispersions of the radiative (R, on the left of the light line) and non-radiative (NR, on the right of the light line) ENZ polariton modes are experimentally measured and theoretically analyzed through the transfer matrix method and the complex-frequency/real-wavenumber analysis, which are in remarkable agreement. We observe directional near-perfect absorption using the Kretschmann geometry for incidence conditions close to the NR-ENZ polariton mode dispersion. Along with field enhancement, this provides us with an unexplored pathway to enhance nonlinear optical processes and to open up directions for ultrafast, tunable thermal emission.

We experimentally demonstrated an epsilon-near-zero (ENZ) mode in an n-doped GaAs layer at 0.8 THz and study its ultrafast dynamics using optical pump terahertz probe spectroscopy. Notable plasmon damping was observed upon optical pumping.

Near-field plasmonic coupling and local field enhancement in metal nanoarchitectures, such as arrangements of nanoparticle clusters, have application in many technologies from medical diagnostics, solar cells, to sensors. Although nanoparticle-based cluster assemblies have exhibited signal enhancements in surface-enhanced Raman scattering (SERS) sensors, it is challenging to achieve high reproducibility in SERS response using low-cost fabrication methods. Here an innovative method is developed for fabricating self-organized clusters of metal nanoparticles on diblock copolymer thin films as SERS-active structures. Monodisperse, colloidal gold nanoparticles are attached via a crosslinking reaction on self-organized chemically functionalized poly(methyl methacrylate) domains on polystyrene-block-poly(methyl methacrylate) templates. Thereby nanoparticle clusters with sub-10-nanometer interparticle spacing are achieved. Varying the molar concentration of functional chemical groups and crosslinking agent during the assembly process is found to affect the agglomeration of Au nanoparticles into clusters. Samples with a high surface coverage of nanoparticle cluster assemblies yield relative enhancement factors on the order of 109while simultaneously producing uniform signal enhancements in point-to-point measurements across each sample. High enhancement factors are associated with the narrow gap between nanoparticles assembled in clusters in full-wave electromagnetic simulations. Reusability for small-molecule detection is also demonstrated. Thus it is shown that the combination of high signal enhancement and reproducibility is achievable using a completely non-lithographic fabrication process, thereby producing SERS substrates having high performance at low cost. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Improving the sensitivity of infrared detectors is an essential step for future applications, including satellite- and terrestrial-based systems. We investigate nanoantenna-enabled detectors (NEDs) in the infrared, where the nanoantenna arrays play a fundamental role in enhancing the level of absorption within the active material of a photodetector. The design and optimization of nanoantenna-enabled detectors via full-wave simulations is a challenging task given the large parameter space to be explored. Here, we present a fast and accurate fully analytic circuit model of patch-based NEDs. This model allows for the inclusion of real metals, realistic patch thicknesses, non-absorbing spacer layers, the active detector layer, and absorption due to higher-order evanescent modes of the metallic array. We apply the circuit model to the design of NED devices based on Type II superlattice absorbers, and show that we can achieve absorption of ∼70% of the incoming energy in subwavelength (∼λ/5) absorber layers. The accuracy of the circuit model is verified against full-wave simulations, establishing this model as an efficient design tool to quickly and accurately optimize NED structures.

Considering the power constrained scaling of silicon complementary metal-oxide-semiconductor technology, the use of high mobility III–V compound semiconductors such as In0.53Ga0.47As in conjunction with high-κ dielectrics is becoming a promising option for future n-type metal-oxide-semiconductor field-effect-transistors. Development of low dissipation field-effect tunable III–V based photonic devices integrated with high-κ dielectrics is therefore very appealing from a technological perspective. In this work, we present an experimental realization of a monolithically integrable, field-effect-tunable, III–V hybrid metasurface operating at long-wave-infrared spectral bands. Our device relies on strong light-matter coupling between epsilon-near-zero (ENZ) modes of an ultra-thin In0.53Ga0.47As layer and the dipole resonances of a complementary plasmonic metasurface. The tuning mechanism of our device is based on field-effect modulation, where we modulate the coupling between the ENZ mode and the metasurface by modifying the carrier density in the ENZ layer using an external bias voltage. Modulating the bias voltage between ±2 V, we deplete and accumulate carriers in the ENZ layer, which result in spectrally tuning the eigenfrequency of the upper polariton branch at 13 μm by 480 nm and modulating the reflectance by 15%, all with leakage current densities less than 1 μA/cm2. Our wavelength scalable approach demonstrates the possibility of designing on-chip voltage-tunable filters compatible with III–V based focal plane arrays at mid- and long-wave-infrared wavelengths.

Optical communication systems increasingly require electro-optical modulators that deliver high modulation speeds across a large optical bandwidth with a small device footprint and a CMOS-compatible fabrication process. Although silicon photonic modulators based on transparent conducting oxides (TCOs) have shown promise for delivering on these requirements, modulation speeds to date have been limited. Here, we describe the design, fabrication, and performance of a fast, compact electroabsorption modulator based on TCOs. The modulator works by using bias voltage to increase the carrier density in the conducting oxide, which changes the permittivity and hence optical attenuation by almost 10 dB. Under bias, light is tightly confined to the conducting oxide layer through nonresonant epsilon-near-zero (ENZ) effects, which enable modulation over a broad range of wavelengths in the telecommunications band. Our approach features simple integration with passive silicon waveguides, the use of stable inorganic materials, and the ability to modulate both transverse electric and magnetic polarizations with the same device design. Using a 4-μm-long modulator and a drive voltage of 2 Vpp, we demonstrate digital modulation at rates of 2.5 Gb/s. We report broadband operation with a 6.5 dB extinction ratio across the 1530–1590 nm band and a 10 dB insertion loss. This work verifies that high-speed ENZ devices can be created using conducting oxide materials and paves the way for additional technology development that could have a broad impact on future optical communications systems.

Recently there has been a large interest in achieving metasurface resonances with large quality factors. In this article, we examine metasurfaces that comprised a finite number of magnetic dipoles oriented parallel or orthogonal to the plane of the metasurface and determine analytic formulas for their resonances’ quality factors. These conditions are experimentally achievable in finite-size metasurfaces made of dielectric cubic resonators at the magnetic dipole resonance. Our results show that finite metasurfaces made of parallel (to the plane) magnetic dipoles exhibit low quality factor resonances with a quality factor that is independent of the number of resonators. More importantly, finite metasurfaces made of orthogonal (to the plane) magnetic dipoles lead to resonances with large quality factors, which ultimately depend on the number of resonators comprising the metasurface. In particular, by properly modulating the array of dipole moments by having a distribution of resonator polarizabilities, one can potentially increase the quality factor of metasurface resonances even further. These results provide design guidelines to achieve a sought quality factor applicable to any resonator geometry for the development of new devices such as photodetectors, modulators, and sensors.

We experimentally demonstrate a functional silicon metadevice at telecom wavelengths that can efficiently control the wavefront of optical beams by imprinting a spatially varying transmittance phase independent of the polarization of the incident beam. Near-unity transmittance efficiency and close to 0–2π phase coverage are enabled by utilizing the localized electric and magnetic Mie-type resonances of low-loss silicon nanoparticles tailored to behave as electromagnetically dual-symmetric scatterers. We apply this concept to realize a metadevice that converts a Gaussian beam into a vortex beam. The required spatial distribution of transmittance phases is achieved by a variation of the lattice spacing as a single geometric control parameter.

Metallic nanocavities with deep subwavelength mode volumes can lead to dramatic changes in the behavior of emitters placed in their vicinity. This collocation and interaction often leads to strong coupling. Here, we present for the first time experimental evidence that the Rabi splitting is directly proportional to the electrostatic capacitance associated with the metallic nanocavity. The system analyzed consists of different metamaterial geometries with the same resonance wavelength coupled to intersubband transitions in quantum wells.

We demonstrate efficient third harmonic generation from a 21.6nm-thick indium tin oxide film on glass substrate for a pump fundamental wavelength of 1350nm using the field enhancement properties of optical modes supported by epsilon-near-zero media.

Metallic films much thinner than the skin depth can support surface plasmon modes whose dispersion approaches the plasma frequency, giving rise to the so-called epsilon-near-zero mode. We analyse its features and observation conditions.

Dielectric resonators represent a promising path toward low loss metamaterials at optical frequencies. In this paper we describe a methodology for tailoring the design of metamaterial resonators as well as recovering their polarizibilies. Examples are provided spanning the range from an isolated resonator with designed scattering properties, to two- and three-dimensional metamaterial arrays exhibiting artificial magnetic properties.

We present the design, realization and characterization of strong coupling between an intersubband transition and a monolithic metamaterial nanocavity in the mid-infrared spectral range. We use a ground plane in conjunction with a planar metamaterial resonator for full three-dimensional confinement of the optical mode. This reduces the mode volume by a factor of 1.9 compared to a conventional metamaterial resonator while maintaining the same Rabi frequency. The conductive ground plane is implemented using a highly doped n+ layer which allows us to integrate it monolithically into the device and simplify fabrication.

We experimentally demonstrate the magnetic mirror behavior of all-dielectric metasurfaces at optical frequencies through phase measurements using time-domain-spectroscopy. The unique boundary conditions of magnetic mirrors can lead to advances in sensors, photodetectors and light sources.

We experimentally demonstrate single beam directional perfect absorption (to within experimental accuracy) of p-polarized light in the near-infrared using unpatterned, deep subwavelength films of indium tin oxide (ITO) on Ag. The experimental perfect absorption occurs slightly above the epsilon-near-zero (ENZ) frequency of ITO where the permittivity is less than one. Remarkably, we obtain perfect absorption for films whose thickness is as low as ~1/50th of the operating free-space wavelength and whose single pass attenuation is only ~ 5%. We further derive simple analytical conditions for perfect absorption in the subwavelength-film regime that reveal the constraints that the ITO permittivity must satisfy if perfect absorption is to be achieved. Then, to get a physical insight on the perfect absorption properties, we analyze the eigenmodes of the layered structure by computing both the real-frequency/complex-wavenumber and the complex-frequency/real-wavenumber modal dispersion diagrams. These analyses allow us to attribute the experimental perfect absorption behavior to the crossover between bound and leaky behavior of one eigenmode of the layered structure. Both modal methods show that perfect absorption occurs at a frequency slightly larger than the ENZ frequency, in agreement with experimental results, and both methods predict a second perfect absorption condition at higher frequencies attributed to another crossover between bound and leaky behavior of the same eigenmode. Our results greatly expand the list of materials that can be considered for use as ultrathin perfect absorbers and also provide a methodology for the design of absorber systems at any desired frequency., Comment: 14 pages, 9 figures

We first introduce the formulation of 2D periodic dyadic Green's function to account for all the field contributions required to thoroughly describe the physics of a 2D array of nanospheres on top of a multilayered substrate. Then, we analyze substrate effects onto complex modes and optical properties of 2D arrays of linear trimers of plasmonic nanospheres and show that Fano resonant features appear for oblique TM-polarized plane wave incidence illumination. These features are attributed to the forced excitation of free modes supported by the array, here computed via modal analysis. We observe strengthened Fano features due to the presence of the multilayered substrate. © 2013 IEEE.

In this work, we study the electromagnetic properties of a metamaterial made by a cubic array of TiO2 microspheres embedded in a host medium at terahertz frequencies. By employing the method reported in [1] by Silveirinha, we are able to consider in the computation the effect of magnetoelectric coupling between TiO2 microspheres, as well as spatial dispersion. After calculation of the dominant mode inside the structure, we show that the effect of spatial dispersion on the effective parameters for this kind of systems is relatively weak. Accuracy of the results and effectiveness of homogenized parameters have been demonstrated by comparison against full-wave simulations for a 5-layer slab of such a metamaterial.

We demonstrate experimentally signatures and dispersion control of surface plasmon polaritons from 1 to 1.8 µm using periodic multilayer metallo-dielectric hyperbolic metamaterials. The fabricated structures are comprised of smooth films with very low metal filling factor. The measured dispersion properties of these hyperbolic metamaterials agree well with calculations using transfer matrix, finite-difference time-domain, and effective medium approximation methods despite using only 2.5 periods. The enhancement factor in the local photonic density of states from the studied samples in the near-infrared wavelength region is determined to be 2.5-3.5. Development of this type of metamaterial is relevant to sub-wavelength imaging, spontaneous emission and thermophotovoltaic applications.

Discrete clusters of closely spaced Au nanoparticles can be utilized in devices from photovoltaics to molecular sensors because of the formation of strong local electromagnetic field enhancements when illuminated near their plasmon resonance. In this study, scalable, chemical self-organization methods are shown to produce Au nanoparticle clusters with uniform nanometer interparticle spacing. The performance of two different methods, namely electrophoresis and diffusion, for driving the attachment of Au nanoparticles using a chemical cross-linker on chemically patterned domains of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) thin films are evaluated. Significantly, electrophoresis is found to produce similar surface coverage as diffusion in 1/6th of the processing time with an ∼2-fold increase in the number of Au nanoparticles forming clusters. Furthermore, average interparticle spacing within Au nanoparticle clusters was found to decrease from 2-7 nm for diffusion deposition to approximately 1-2 nm for electrophoresis deposition, and the latter method exhibited better uniformity with most clusters appearing to have about 1 nm spacing between nanoparticles. The advantage of such fabrication capability is supported by calculations of local electric field enhancements using electromagnetic full-wave simulations from which we can estimate surface-enhanced Raman scattering (SERS) enhancements. In particular, full-wave results show that the maximum SERS enhancement, as estimated here as the fourth power of the local electric field, increases by a factor of 100 when the gap goes from 2 to 1 nm, reaching values as large as 1010, strengthening the usage of electrophoresis versus diffusion for the development of molecular sensors. © 2013 American Chemical Society.