Gap-surface Plasmon Resonances Research Articles

A wide angle broadband solar absorber with a horizontal multi-cylinder structure based on an MXene material.

An MXene material absorbs visible and IR light which makes a MXene-based solar absorber an ideal absorber. Here, we propose a high-absorption broadband absorber based on an array of MXene composite cylinder ring structures. The structure designed in this article fully utilizes the MXene material's large surface area to volume ratio, and in the wavelength range of 300-5000 nm, the average absorption efficiency is as high as 98.44%, and the energy absorption rate in the AM 1.5 solar radiation spectrum is 98.76%. The absorption characteristics of the absorber are analyzed by using the finite-difference time-domain (FDTD) method. The electric and magnetic field patterns indicate that the high absorption performance is attributed to the coupling effect of surface plasmon resonance and gap surface plasmon resonance. Furthermore, the absorber exhibits insensitivity to the polarization angle and demonstrates high absorption efficiency even at large incidence angles. Within a certain manufacturing tolerance range, the absorber can still maintain its broadband absorption characteristics. The absorber also shows a high thermal emissivity of 98.5% when the temperature is 1750 K. The findings offer a theoretical foundation for the development of absorption metamaterials for solar energy harvesting elements.

Plasmonic Coupled Modes in a Metal-Dielectric Periodic Nanostructure.

In this study we investigate the optical properties of a 2D-gap surface plasmon metasurface composed of gold nanoblocks (nanoantennas) arranged in a metal-dielectric configuration. This novel structure demonstrates the capability of generating simultaneous multi-plasmonic resonances and offers tunability within the near-infrared domain. Through finite difference time domain (FDTD) simulations, we analyze the metasurface's reflectance spectra for various lattice periods and identify two distinct dips with near-zero reflectance, indicative of resonant modes. Notably, the broader dip at 1150 nm exhibits consistent behavior across all lattice periodicities, attributed to a Fano-type hybridization mechanism originating from the overlap between localized surface plasmons (LSPs) of metallic nanoblocks and surface plasmon polaritons (SPPs) of the underlying metal layer. Additionally, we investigate the influence of dielectric gap thickness on the gap surface plasmon resonance and observe a blue shift for smaller gaps and a spectral red shift for gaps larger than 100 nm. The dispersion analysis of resonance wavelengths reveals an anticrossing region, indicating the hybridization of localized and propagating modes at wavelengths around 1080 nm with similar periodicities. The simplicity and tunability of our metasurface design hold promise for compact optical platforms based on reflection mode operation. Potential applications include multi-channel biosensors, second-harmonic generation, and multi-wavelength surface-enhanced spectroscopy.

Visible and Near-Infrared Broadband Absorber Based on Ti3C2Tx MXene-Wu.

A high absorption broadband absorber based on MXene and tungsten nanospheres in visible and near-infrared bands is proposed. The absorber has a maximum absorption of 100% and an average absorption of 95% in the wavelength range of 400–2500 nm. The theoretical mechanism and parameter adjustability of the absorber are analyzed by FDTD solutions. The results show that the structural parameters can effectively adjust the absorption performance. The good absorption performance is due to the action of the local surface plasmon resonance coupling with the gap surface plasmon resonance and Fabry–Perot resonance. The simulation results show that the absorber is insensitive to the polarization and oblique incidence angle of incident light, and that high absorption and broadband can be maintained when the oblique incidence angle is up to 60°.

Dynamically tunable second-harmonic generation using hybrid nanostructures incorporating phase-change chalcogenides.

Nonlinear metasurfaces with high conversion efficiencies have been vastly investigated. However, strong dynamic tunability of such devices is limited in conventional passive plasmonic and dielectric material platforms. Germanium antimony telluride (GST) is a promising phase-change chalcogenide for the reconfiguration of metamaterials due to strong nonvolatile changes of the real andimaginary parts of the refraction index through amorphous-crystalline phase change. The orderly structured GST has an even higher potential in tunable second-harmonic generation (SHG) with a non-centrosymmetric crystal structure at the crystalline phase, while the amorphous phase of GST does not exhibit bulk second-order nonlinearity. Here, we experimentally demonstrate SHG switches by actively controlling the crystalline phase of GST for a GST-based hybrid metasurface featuring a gap-surface plasmon resonance, and a quarter-wave asymmetric Fabry-Perot (F-P) cavity incorporating GST. Weobtain SHG switches with modulation depths as high as ∼ 20dB for the wavelengths at the on-state resonance. Wealso demonstrate the feasibility of multi-level SHG modulation by leveraging three controlled GST phases, i.e.,amorphous, semi-crystalline, and crystalline, for the gap-surface plasmon hybrid device, which features stronger light-matter interaction and has higher resonant SHGefficiencies than the asymmetric F-P cavity device atrespective GST phases. This research reveals that GST-based dynamic SHG switches can be potentially employed in practical applications, such as microscopy, optical communication, and photonic computing in the nonlinear regime.

Dispersion of resonant modes in patch antenna lattices.

Spectroscopic polar angle resolved Mueller matrix ellipsometry at multiple azimuthal incidences, together with a full-field model, reveal new details in the interplay between localized gap surface plasmon resonances and propagating surface plasmon polaritons (SPPs) in a rectangular array of metal-insulator-metal patches. A plane-wave expansion of the field in the insulator shows that the fundamental localized resonances are composed of oppositely propagating modes. Sharp dispersive resonances observed in p-polarization, excited near the opening of diffracted orders, are shown to be grating coupled SPPs. The SPPs show strong coupling with localized modes of similar symmetry, while they appear suppressed by modes of dissimilar symmetry.

Active-Tuning and Polarization-Independent Absorber and Sensor in the Infrared Region Based on the Phase Change Material of Ge2Sb2Te5 (GST)

Phase-change materials (PCMs), possessing thermo-optic and thermo-electric properties, have constantly enabled the rewritable optical data storage and the commercialized phase-change memory devices. In particular, Ge2Sb2Te5 (GST) has been considered for configurable photonics applications, such as active dielectric metasurface. In this paper, we report an active absorber with metal-insulator-metal (MIM) scheme with GST in the infrared region. The absorber consists of Al disk and reflective Al film with a GST spacer layer. Extraordinary absorption with peaks of more than 90% can be achieved over a broad bandwidth, attributing to highly confined gap surface plasmon resonance. In addition, the absorption can be tuned via adjusting the proportion of GST crystallization, which is a unique advantage to design active device. Meanwhile, the absorption is polarization-independent owing to its structural symmetry. Furthermore, we introduce the designed absorber to the application of sensing. This nearly perfect absorbing strategy offers great potential in sensing applications due to its flexibility and polarization-independence.

Third-order gap plasmon based metasurfaces for visible light.

Efficient control and manipulation of light using metasurfaces requires high fabrication accuracy that becomes progressively demanding when decreasing the operation wavelength. Considering gap surface plasmon (GSP) based metasurfaces, we demonstrate that the metasurfaces, which utilize the third-order GSP resonance and thereby involve relatively large nanobricks, can successfully be used for efficient polarization-controlled steering of visible light. The reflection amplitude and phase maps for a 450 nm period array of 50 nm thick nanobricks placed atop a 40 nm thick silica layer supported by an optically thick gold film are calculated for the operation wavelength of 633 nm. Exploiting the occurrence of the third-order GSP resonance for nanobricks having their lengths close to 300 nm, we design the phase-gradient metasurface, representing an array of (450 x 2250 nm2) supercells made of 5 nanobricks with different dimensions, to operate as a polarization beam splitter for linearly polarized light. The fabricated polarization beam splitter is characterized using a supercontinuum light source at the normal light incidence and found to exhibit a polarization contrast ratio of up to 40 dB near the design wavelength of 633 nm while showing better than 20 dB contrast in the range of 550 - 650 nm for both polarizations. The diffraction efficiency experimentally measured at normal incidence exceeds 10% (20% in simulations) at the design wavelength of 633 nm, with the performance for the TE polarization (electric field perpendicular to the plane of diffraction) being significantly better (experimentally > 20% and theoretically > 40%) than for the TM polarization. This difference becomes even more pronounced for the light incidence deviating from normal. Finally, we discuss possible improvements of the performance of polarization beam splitters based on third-order GSP resonance as well as other potential applications of the suggested approach.

Zinc Oxide Based Plasmonic Multilayer Resonator: Localized and Gap Surface Plasmon in the Infrared

Using alternative plasmonic materials, we experimentally demonstrate gap plasmon resonances in metal–insulator–metal nanostructures in the near- and mid-infrared wavelength regions utilizing gallium doped zinc oxide as the metallic component and undoped zinc oxide as the dielectric. We show that similar to metal–insulator–metal resonators previously demonstrated with noble metals, the layered transparent conducting oxide nanodisks support gap surface plasmon resonances characterized by highly confined electromagnetic fields in the dielectric gap. Such resonances can be tailored to desired values by varying the dielectric-layer thickness. Utilizing these observed gap plasmon resonance, we examine the potential of our structure for sensing applications by measuring the surface enhanced infrared absorption of an octadecanethiol layer. The layered nanostructure can detect very weak absorption resonances in nanoscale volumes of absorbing material deposited over the nanodisk resonator.

Gold Photoluminescence Wavelength and Polarization Engineering

We demonstrate engineering of the spectral content and polarization of photoluminescence (PL) from arrayed gold nanoparticles atop a subwavelength-thin dielectric spacer and optically thick gold film, a configuration that supports gap-surface plasmon resonances (GSPRs). Choice of shapes and dimensions of gold nanoparticles influences the GSPR wavelength and polarization characteristics, thereby allowing us to enhance and spectrally mold the plasmon-assisted PL while simultaneously controlling its polarization. In order to understand the underlying physics behind the plasmon-enhanced PL, we develop a simple model that faithfully reproduces all features observed in our experiments showing also good quantitative agreement for the PL enhancement.

Analog computing using reflective plasmonic metasurfaces.

Motivated by the recent renewed interest in compact analog computing using light and metasurfaces ( Silva, A. et al. Science 2014 , 343, 160 - 163), we suggest a practical approach to its realization that involves reflective metasurfaces consisting of arrayed gold nanobricks atop a subwavelength-thin dielectric spacer and optically thick gold film, a configuration that supports gap-surface plasmon resonances. Using well-established numerical routines, we demonstrate that these metasurfaces enable independent control of the light phase and amplitude, and design differentiator and integrator metasurfaces featuring realistic system parameters. Proof-of-principle experiments are reported along with the successful realization of a high-quality poor-man's integrator metasurface operating at the wavelength of 800 nm.

Broadband plasmonic half-wave plates in reflection

We demonstrate, both numerically and experimentally, that metal-insulator-metal configurations in which the top metal layer consists of a periodic arrangement of nanobricks, thus supporting gap-surface plasmon resonances, can be designed to function as reflective broadband half-wave plates. Using gold as the metal, the constructed wave plates in the near-infrared regime show scalability, bandwidth of ~20% of the design wavelength, and theoretical reflectivity above 85%, while a reflectivity of ~50% is experimentally measured.

Efficient and broadband quarter-wave plates by gap-plasmon resonators

We demonstrate numerically that metal-insulator-metal (MIM) configurations in which the top metal layer consists of a periodic arrangement of nanobricks, thus facilitating gap-surface plasmon resonances, can be designed to function as efficient and broadband quarter-wave plates in reflection by a proper choice of geometrical parameters. Using gold as the metal, we demonstrate quarter-wave plate behavior at λ ~/= 800 nm with an operation bandwidth of 160 nm, conversion efficiency of 82%, and angle of linear polarization fixed throughout the entire bandwidth. This work also includes a detailed analytical and numerical study of the optical properties and underlying physics of structured MIM configurations.