Nanodisk Arrays Research Articles

Polarization-independent ultranarrow ultraviolet graphene perfect absorption for temperature controlled high-performance optical switch

We demonstrate a tunable polarization-independent ultranarrow perfect absorption (PA) in a hybrid metasurface consisting of graphene-dielectric nanodisk-metal mirror in the ultraviolet (UV) range. Through near-field interactions between the optical dissipation of graphene and surface plasmon polaritons supported by Al2O3 nanodisk array on UV mirror, the UV Fano-like absorption peak can reach 99.92% with linewidth as low as 3.4 nm, which is predicted by the impedance matching theory and a Fano model. Furthermore, a dynamic tuning of the UV PA and the associated high-performance optical switch are achieved via temperature change of the encapsulated ethanol. Importantly, the modulation depth of almost 100%, the ultralarge modulation intensity of about 2.5×106 and the on/off ratio of 63 dB are reached for the graphene-based switch by a thermal control. Our work holds potential applications on the UV graphene based light modulators such as high-precision optical switch and nanodevices.

Optical control of spin waves in hybrid magnonic-plasmonic structures.

Magnonics, which harnesses the unique properties of spin waves, offers promising advancements in data processing due to its broad frequency range, nonlinear dynamics, and scalability for on-chip integration. Effective information encoding in magnonic systems requires precise spatial and temporal control of spin waves. Here, we demonstrate the rapid optical control of spin-wave transport in hybrid magnonic-plasmonic structures. By using thermoplasmonic heating in yttrium iron garnet films integrated with gold nanodisk arrays, we achieve a suppression of spin-wave signals by 20 dB using single laser pulses lasting just a few hundred nanoseconds. Our results reveal a strong correlation between plasmonic light absorption and spin-wave manipulation, as supported by micromagnetic simulations that emphasize the crucial role of magnonic refraction. This study establishes thermoplasmonics as a powerful tool for controlling spin-wave propagation, bridging the fields of magnonics and plasmonics, and paving the way for the development of multifunctional hybrid magnonic devices.

Chiral Light-Matter Interactions with Thermal Magnetoplasmons in Graphene Nanodisks.

We investigate the emergence of self-hybridized thermal magnetoplasmons in doped graphene nanodisks at finite temperatures upon being subjected to an external magnetic field. Using a semianalytical approach, which fully describes the eigenmodes and polarizability of the graphene nanodisks, we show that the hybridization originates from the coupling of transitions between thermally populated Landau levels and localized magnetoplasmon resonances of the nanodisks. Owing to their origin, these modes combine the extraordinary magneto-optical response of graphene with the strong field enhancement of plasmons, making them an ideal tool for achieving strong chiral light-matter interactions, with the additional advantage of being tunable through carrier concentration, magnetic field, and temperature. As a demonstration of their capabilities, we show that the thermal magnetoplasmons supported by an array of graphene nanodisks enable chiral perfect absorption and chiral thermal emission.

Chiral optical properties of metasurfaces comprised of chiral media: effects of geometric and material chirality

We deconvolute the distinct and sometimes competing effects of geometric and material chirality in metastructures created from materials that are intrinsically chiral. We find that overlapping Mie-like resonances in nanodisk arrays leads to 6-fold CD enhancement compared to a uniform film. Furthermore, making the medium chiral does not necessarily increase CD; enhancement depends on the magnitude of the Pasteur parameter and its real and imaginary components. Finally, to demonstrate how geometric and material chirality can be combined, we design a geometrically chiral meta-atom out of chiral media and observe over 9-fold enhancement in both CD and g-factor compared to a metasurface comprised of achiral material.

Ultra-broadband perfect solar absorber based on V2O5−TiN−V2O5 nanodisc and TiN nanopillar array structures

Ultra-broadband perfect solar absorber based on V2O5−TiN−V2O5 nanodisc and TiN nanopillar array structures

Increasing the electric field amplification in the metal-insulator-metal structure with a grating hybrid of bowtie nanotriangle and cylindrical nanodisc

In this paper, the strong electromagnetic coupling between an integrated grating of an array of periodic gold nanodiscs and an array of bowtie nanotriangles placed on layers of a dielectric and a metal has been investigated. The upper layer is periodically created by removing each nanodisk in the array of nanodisks and replacing it with bowtie nanotriangles. The structure for near field radiation with linear polarization at 800 nm wavelength is optimized so that it has the highest amount of amplification in the gap space between the tips of the nanotriangle with a minimum value of 188 times and a maximum of 320 times. The simulation results confirm that the huge field enhancement obtained is due to the strong coupling between the LSPR formed in the grating of bowties nano triangle and nanodiscs and the SPPs formed in the metal film. The amount of amplification compared to the array of only nanodiscs (about 32 times) or only bowtie nano triangles (about 120 times) is not only higher, but also the anti-crossing behavior is observed. The high amplification obtained at the mentioned wavelength can be used for laser oscillators with a central wavelength of 800 nm, such as titanium sapphire, etc., which has many applications in near-field physics, SERS, and ultrafast lasers.

Plasmonic coupling effect of annealed gold nanoarrays

Periodic metal nanodisc arrays have the potential to exhibit regularly spaced large local field enhancements, especially when high-Q collective plasmonic grating resonances can be obtained. Here we demonstrate how Laser interference lithography (LIL) as a maskless and high throughput technique can be used to fabricate these on square centimeter areas. The drawback of LIL is the rather fixed ratio of the size of the individual nanostructure (d) to the period of the array (p) of about d/p ∼ 0.5 for the setup used in the current article, thereby, limiting its ability to create resonances with ultra-high quality factors (Q-factors). To improve the Q-factor of the resonances of the arrays, we study the effect of thermal annealing nanodisk arrays fabricated by LIL and a lift off process. The nanodisk arrays with periods of 400 nm and 500 nm exhibited a plasmonic resonance, which was caused by the interaction of the single disk resonance and a (1 0) grating resonance. Annealing for a short duration lowered the d/p ratio from 0.5 to 0.4, and led to smoothening of the disk surfaces and growth of gold grains, resulting in lower ohmic and radiative losses and doubling of the Q-factor of the resonances. Finite element method (FEM) simulations were used to monitor this improvement in material parameters. Annealing for a longer duration disintegrated the nanodisk into several smaller particles while maintaining the overall periodicity of the array. While the plasmonic resonances of the experimentally investigated fragmented disks were basically destroyed, simulation predict that for larger periods fragmented nanodisk arrays (keeping the d/p ∼ 0.4) can exhibit extremely strong and sharp resonances whose Q-factor increases more than 58.4 times compared to the unfragmented discs. In addition, simulations show a massive enhancement of the local electric field promising immense potential for surface enhanced Raman sensing.

Plasmonic Coupling for High‐Sensitivity Detection of Low Molecular Weight Molecules

This article presents a novel plasmonic sensing platform designed for the detection of low molecular weight molecules, offering significant advancements in diagnostic applications. The platform features a periodic array of gold nanodisks on a 20 nm thin silica layer, supported by a 100 nm thick gold substrate. By leveraging the coupling between localized and propagating surface plasmon resonances, this design significantly enhances the sensitivity and specificity of molecular detection. Finite element method simulations are conducted to characterize the optical properties and reflectance response of the nanodisks array in the visible to near‐infrared range. Ellipsometric analysis is performed to measure the reflectance of the sample at various angles. Additionally, scanning near‐field optical microscopy in reflectance mode validates the design by revealing well‐defined plasmonic hot spots and interference patterns consistent with the simulated results. The findings demonstrate the platform's effectiveness in amplifying optical signals, achieving a limit of detection of 50 μM for molecules with a molecular weight of less than 1 KDa. This high sensitivity and specificity highlight the potential of the proposed plasmonic platform to advance the development of highly sensitive sensors for low molecular weight molecules, making it a valuable tool for diagnostics and precise molecular detection.

A Fiber optics based surface enhanced Raman spectroscopy sensor for chemical and biological sensing

This paper investigates an innovative surface-enhanced Raman scattering (SERS) sensor developed on a side-polished multimode optical fiber core. The optical fiber was integrated into specifically designed 3-dimensional printed mold, where manual polishing of the fiber took place. Microsphere Photolithography (MPL) techniques was employed to pattern periodic nanoantenna arrays on the polished surface, incorporating multiple disk diameters at a fixed periodicity. Subsequent gold deposition/lift-off were carried out to transfer the pattern from the photoresist to the fiber core, resulting in highly periodic hexagonal closed pack (HCP) arrays of nanodisks. These arrays can significantly enhance the SERS signal intensity compared to that of the fiber tip. The sensor's performance was demonstrated using various concentrations of Rhodamine 6G (R6G) dye ranging from 10−5 to 10−9 M as a function of disk diameter and sensing surface area. The resulting spectra revealed characteristic peak positions that aligned well with the fingerprint Raman spectra of R6G. The results demonstrates that the sensitivity is 10−9 M for the sensor with an 800 nm disk diameter.

Comparative Analysis of Two Different MIM Configurations of a Plasmonic Nanoantenna

AbstractTwo plasmonic nanoantenna configurations—nanodisk and nanostrip arrays—in a metal–insulator-metal (MIM) setup were proposed, optimized, and compared by simulating their optical properties in three-dimensional models using COMSOL Multiphysics software. The optical responses, including electric field enhancement, absorption, reflection, and transmission spectra, were systematically investigated. Optimized geometrical parameters led to a significant enhancement of the electric field within the gap layers and almost perfect light absorptance for both structures. The results showed that the enhancement of the electric field depends on the polarization of the incident light. For both polarizations, the periodic circular nanodisk array showed a stronger field enhancement with an electric field enhancement factor of 6.6 × 106 and TE polarization, and a larger absorptance of 98% at its dipole resonance wavelength, indicating the fundamental plasmonic mode. In addition, weaker resonant modes were observed in the absorptance and reflectance spectra of both nanostructures, with the nanostrips exhibiting sharper and stronger higher-order modes, making them suitable for applications requiring precise wavelength selectivity and narrow-band responses. Despite their different geometric shapes, both structures exhibited similar optimized metal film thickness and nanoparticle height, comparable modes in number and position, and identical optimized light incidence angles. Furthermore, increasing the dielectric gap layer thickness and optimizing it to a specific value revealed its ability to measure the refractive index, making it a promising candidate for sensing applications.

Diffraction of harmonic generation in metasurfaces of quasi-BICs induced by geometrical perturbations

We report the diffraction behavior of harmonic generation in metasurfaces of quasi-bound states in the continuum (BICs) induced by geometrical perturbations. Conventionally, the geometrical perturbation can transform the symmetry-protected BICs into quasi-BICs in metasurfaces for many important applications. Such geometrical perturbations sometimes lead to the doubled period of metasurfaces, and then dramatically affect the diffraction of light, especially the harmonic generation light of shorter wavelengths. Here, we investigate the efficiency and diffraction angles of different orders of second and third harmonic generation in two typical metasurfaces of quasi-BICs induced by geometrical perturbation, i.e., compound grating waveguide nanostructures and zig-zag nanodisk arrays. The results are important to understand the diffraction behavior of harmonic generation in the period doubled or tripled nanostructures due to geometry perturbations, and to realize the efficient multi-channel nonlinear sources.

All-Optical Control of Vortex Lasing in Silicon-Organic Lattices.

This paper reports a silicon-organic hybrid lattice that can lase with vortex emission and allow all-optical control. We combine an array of amorphous silicon nanodisks with gain from dye molecules in organic solvents to generate vortex lasing from bound states in the continuum under pulsed optical pumping. Irradiating the device with an additional continuous wave green laser beam can cause optical heating in silicon and lead to negative change in the refractive index of the organic solvents; meanwhile, the green laser beam can provide additional gain. Dynamic tuning of the lasing wavelength is achieved by varying the intensity of the controlling beam. Furthermore, the vortex beam lasing can be switched to single-lobed beam lasing by moving the controlling spot to break the in-plane symmetry within the pumping spot. Our findings could shed new light on active silicon topological devices.

Multipole couplings in dielectric nanodisk arrays and their polarization effects.

In this paper, we study the optical properties of a planar array consisting of nanodisks using the coupled multipole model (CMM). As we demonstrate, this model shows its advantages in uncovering the complex inter-particle mutual interaction mechanisms, which are usually obscured by direct numerical simulations. We first propose a method to compute the polarizabilities of the individual non-spherical particles up to the magnetic quadrupole. Then, the multipole moments of the arrayed nanodisks can be readily calculated. Using the results, we were able to trace the dominant contributions from the various couplings between these multipole sources. From such analysis, we reveal the mechanisms of multipole resonance shifts and possible manipulation strategies. These insights rendered by the CMM make it possible to design the array as a polarizer by tuning the lattice periods. We further evaluated the polarizer performance under different working wavelengths and incident angles. As the disk shape is relatively less challenging for fabrication, our model shows great promise in optimizing and designing functional structures for nano-optics applications.

Metasurface of Strongly Coupled Excitons and Nanoplasmonic Arrays.

Metasurfaces allow light to be manipulated at the nanoscale. Integrating metasurfaces with transition metal dichalcogenide monolayers provides additional functionality to ultrathin optics, including tunable optical properties with enhanced light-matter interactions. In this work, we demonstrate the realization of a polaritonic metasurface utilizing the sizable light-matter coupling of excitons in monolayer WSe2 and the collective lattice resonances of nanoplasmonic gold arrays. We developed a novel fabrication method to integrate gold nanodisk arrays in hexagonal boron nitride and thus simultaneously ensure spectrally narrow exciton transitions and their immediate proximity to the near-field of array surface lattice resonances. In the regime of strong light-matter coupling, the resulting van der Waals metasurface exhibits all key characteristics of lattice polaritons, with a directional and linearly polarized far-field emission profile dictated by the underlying nanoplasmonic lattice. Our work can be straightforwardly adapted to other lattice geometries, establishing structured van der Waals metasurfaces as means to engineer polaritonic lattices.

Substrate-induced hybridization of plasmon modes in the composite nanostructure of nanodisk array/thin film for spectrum modulation.

Hybridization coupling among plasmon modes is an effective approach to manipulate near-field properties thus optical spectral shapes of plasmonic nanostructures. Generally, mode hybridization coupling is achieved by modifying the topography and dimensions of nanostructures themselves, with few concerns about substrate-induced manipulation. Herein, we propose a composite nanostructure consisting of a gold (Au) nanodisk array and a thin Au film supported by a dielectric substrate. In this configuration, both the refractive index of the dielectric substrate and thin gold film's thickness mediate the interaction of plasmon modes supported by upper and lower interfaces of the composite nanostructure, resulting in two hybridized plasmon modes. We systematically investigate the relationship between optical fields at the top surface of plasmon modes before and after the hybridization coupling. Specifically, the near-field amplitude at the top surface of the unhybridized modes is stronger than that of individual hybridized mode, and lower than the near-field summation of these two hybridized modes. This work not only provides a straightforward strategy for generating two plasmon modes in a nanostructure but also elucidates the variation of the optical field during the hybridization process, which is of crucial significance for applications, such as upconversion enhancement and multi-resonance sensing.

Flexible plasmonic display featuring differentiated and localized control over transmission and reflection

Structural colors using metal materials, plasmonic color generation, can confine optical excitation beyond the diffraction limit owing to nanoscale metals with high efficiency in light absorption and scattering. They have several advantages over conventional display technology, including superior resolution and long-term preservation. However, most research on plasmonic color generation has been conducted for the development of static color generation, and dynamic tuning remains a challenging issue. To develop dynamic plasmonic colors, electrochemical, liquid crystal, and electromechanical methods have been proposed; however, there have been limitations in repeatability, flexibility, and scale-up processes. To address these problems, this work proposes a flexible dynamic plasmonic display using dielectric elastomer actuators (DEAs) to isotropically control the interdistance between the metal nanostructures, which can show dynamic coloration without polarization distortion. To replace the expensive and small-scale manufacturing approach, shadow masking and transfer technique with the anodic aluminum oxide (AAO) membrane was applied to realize large-scale and uniformly distributed Au nanodisc array. The differentiated and localized color change in the transmission and reflection modes, such as Janus's face, is realized by proper design of Au nanodisc array on the patterned transparent compliant electrodes formed by silver nanowires and PEDOT:PSS composites. Apparent and locally active color changes appeared in the transmission mode, but almost no color changes were observed in the reflection model by DEA actuation. The proposed system has the potential to activate color filters, cryptographic characters, and next generation display technologies.

Soft and hard trimming of imprint resist masks to fabricate silicon nanodisk arrays with different edge roughness

Soft and hard trimming of imprint resist masks to fabricate silicon nanodisk arrays with different edge roughness

Hybrid magneto-plasmonic structure consisting of hexagonal periodic nanodisks array with giant transverse magneto-optical Kerr effect for sensing application

The present study proposes a theoretical design of the magneto-optical surface plasmon resonance (MOSPR) refractive index sensor that utilizes a magnetic field for modulating the dispersion of surface plasmon. This sensor based on the transverse magneto-optical Kerr effect (TMOKE) is constructed using a hybrid magneto-plasmonic film covered with an array of hexagonal periodic Au nanodisks. The structural parameters were optimized to obtain the Fano shape TMOKE response characterized by an extremely narrow bandwidth (0.00997°) and remarkably high amplitude (0.99). The excitation of the optimal surface plasmon resonance (SPR) and the resonance enhancement effect of multi-mode coupling enables us to achieve a surface sensitivity of 207.5 deg RIU−1 and a high figure of merit of the order of 104 RIU−1, surpassing conventional SPR and MOSPR sensors by at least one order of magnitude. The present study offers a comprehensive guideline for the design of high-performance magneto-plasmonic sensors, facilitating instrument miniaturization and manufacturing cost reduction.

Ultra-narrow dual-band perfect absorber based on double-slotted silicon nanodisk arrays

Due to its unique advantage of optical properties, nanophotonic metamaterials have gained extensive applications in perfect absorbers. However, achieving both dual-band and ultra-narrow linewidth in absorbers simultaneously remains a challenge for typical metal-dielectric based metamaterials. In this work, a dual-band ultra-narrow perfect absorber consisting of a double slotted silicon nanodisk array that located on a silver film with a silica spacer layer is proposed theoretically. By combining the hybrid mode excited by the coupling of diffraction wave mode and magnetic dipole mode with the anapole–anapole interaction, two absorption peaks can be induced in the near-infrared regime, achieving nearly perfect absorbance of 99.31% and 99.61%, with ultra-narrow linewidths of 1.92 nm and 1.25 nm respectively. In addition, the dual-band absorption characteristics can be regulated by changing the structural parameters of the as-proposed metamaterials. The as-designed metamaterials can be employed as efficient two-channel refractive index sensors, with sensitivity and figure of merit (FOM) of 288 nm RIU−1 and 150 RIU−1 for the first band, and sensitivity and FOM of up to 204 nm RIU−1 and 163.2 RIU−1 for the second band. This work not only opens up a new design idea for the realization of dual-band perfect absorber synchronously with ultra-narrow linewidth, but also provides potential attractive candidates for developing dual-frequency channel sensors.

Mechanism of formation and evolution of bound states in the continuum of split-hole all-dielectric metasurface under asymmetric displacement perturbation

Bound states in the continuum (BICs) with ultra-high Q properties have attracted much attention for their perfect localization in the continuous spectral range coexisting with extended waves. In this study, breaking the traditional excitation form of structure breakage or excitation field asymmetry, a monolithic silicon nanodisk array with relative displacement generated by the complete splitting of square nanopores is proposed based on the unique electromagnetic properties of all-dielectric metamaterials. During the introduction of perturbations by asymmetric displacements of splitting holes, it is shown by numerical simulations that two BICs at different wavelengths can be realized. Combined with eigenmodes of group theory, the symmetric matching relationship between the symmetry-protected BICs and the free-space radiation during the evolution process is analytically demonstrated, and the formation mechanism and the evolution law of the BICs excited by this metasurface are deeply investigated. meanwhile, it also provides a theoretical basis for the polarization dependence of quasi-BICs excitation and the ultra-high Q factor expression of BICs. Furthermore, near-field distribution and multipole decomposition show that the field distribution and surface currents support the excitation of BIC-driven toroidal dipole and magnetic quadrupole dual modes. This study not only provides an effective reference for the stability of high-Q resonance wavelengths, but also solves the problem of the lack of universality in analyzing the resonance mechanism based on resonance phenomena, and provides solid theoretical support for the study of displacement-mediated BICs resonance excitation and evolution.