Plasmonic Nanostructure Arrays Research Articles

Photofabrication of Chiral Plasmonic Nanostructure Arrays

AbstractChiral plasmonic nanostructures can be potentially applied to chiroptical materials and devices, as well as sensors for chiral molecules. When those are applied to metasurfaces or metamaterials, those would be appropriately oriented and aligned. We therefore prepared arrays of chiral plasmonic nanostructures on the basis of bottom‐up, self‐assembling methods. A triangular Au nanoplate array as an achiral precursor was prepared on a TiO2‐coated substrate by nanosphere lithography. The array was irradiated with right‐ or left‐circularly polarized light (CPL) in a solution containing Pb2+ for site‐selective deposition of PbO2 in a chiral geometry by plasmon‐induced charge separation. The well‐aligned Au−PbO2 nanostructure array thus obtained exhibits circular dichroism, and the handedness of the array can be inverted by changing the rotation direction of the irradiated CPL.

Metallic Plasmonic Nanostructure Arrays for Enhanced Solar Photocatalysis

AbstractPlasmon‐enhanced photocatalysis has emerged as a promising technology for solar‐to‐chemical energy conversion. Compared to isolated or disordered metal nanostructures, by controlling the morphology, composition, size, spacing, and dispersion of individual nanocomponents, plasmonic nanostructure arrays with coupling architectures yield strong broadband light‐harvesting capability, efficient charge transfer, enhanced local electromagnetic fields, and large contact interfaces. Although metallic nanostructure arrays are extensively studied for various applications, such as refractive index sensing, surface‐enhanced spectroscopy, plasmon‐enhanced luminescence, plasmon nanolasing, and perfect light absorption, the connection between surface plasmon resonance and enhanced photocatalysis remains relatively unexplored. In this study, an overview of plasmonic nanostructure arrays over a broad range, from 0D to 3D, for efficient photocatalysis is presented. By reviewing the fundamental mechanisms, recent applications, and latest developments of plasmonic nanostructure arrays in solar‐driven chemical conversion, this study reports on the latest guidance toward the integration of plasmonic nanostructures for functional devices in the fields of plasmonic, photonics, photodetection, and solar‐energy harvesting.

Surface-enhanced Raman scattering for biosensing platforms: a review

ABSTRACT The past few decades have seen rapid advances in surface-enhanced Raman scattering (SERS) techniques which have enabled increasingly efficient detection of infinitesimal molecular traces down to the single molecule. This occurrence paved the way for promising applications, among which the use of SERS in highly efficient label-free optical sensors, thus attaining a large interest, especially in the biomedical field. SERS sensors are realized following different strategies, usually involving the control of size and shape of nanoantennas and the design of nanostructures arrays to precisely set the Localized Surface Plasmon resonances (LSP) and the hot spots positions. However, this may entail the use of lithographic techniques with high fabrication costs. Other approaches are based on disordered arrays of plasmonic nanostructures, much cheaper and easier to fabricate, although the control of the hot spots position and performances is lost. Here we review the more recent SERS strategies approached in order to obtain the desired detection of analytes and specific biomolecular species, ranging from the realization of particularly efficient SERS substrates suitable for hydrated molecules to the creation of hot spots in a liquid environment enabling highly sensitive spectroscopic sensors in the natural habitat of the biomolecules.

Green production of self-assembled silver nanoarrays on flexible substrate for direct detection and catalytic degradation of organic water pollutants

Facile eco-friendly green chemistry assisted (hybrid tea rose petals extract) self- assembled plasmonic silver nano structure arrays (AgNS) were fabricated on a flexible substrate. In-situ self-assembly during the reduction process lead to organize arrays like AgNS with smaller size Ag nanocubes. Synthetic mechanisms detailed with optimizations were deliberately projected with UV–visible absorption spectroscopic studies. Structural studies indicated the cubic system of silver with an average crystalline size of 20 nm. Electron microscopic images elucidate the array like self-assembled Ag cubes; outstand for high phase purity with 95.6% of Ag. As well, UV–vis absorption results confirmed the shape confinement of self-assembled Ag nanocubes with the SPR band located around 450–490 nm. Feasibility of AgNS array in catalytic degradation of Rhodamine B dye tests was assessed with efficient degradation of 97% within 8 min. Ever since AgNS were forthright in field of calorimetry detection, H2O2 calorimetry studies were portrayed. Further on, fabrication of flexible, cost-effective plastic SERS support as sensor was developed with AgNS array (GAFPS) is yet another milestone achieved in SERS sensor platform. Raman probe molecule (Rhodamine 6G (R6G)) was exploited in optimization experiments for SERS detection. The optimized GAFPS SERS sensor involved in detection of Methylene blue (MB) and Rhodamine B (RhB) dyes; Sensor sensitivity studies succeeded with its sensitivity limit down to nano-molar range for RhB whereas close to pico-molar range for MB. In nutshell, multifaceted features of self-assembled plasmonic AgNS brings in state of art in the detection and degradation of industrial waste water management systems.

Microfluidics-Based Plasmonic Biosensing System Based on Patterned Plasmonic Nanostructure Arrays.

This review aims to summarize the recent advances and progress of plasmonic biosensors based on patterned plasmonic nanostructure arrays that are integrated with microfluidic chips for various biomedical detection applications. The plasmonic biosensors have made rapid progress in miniaturization sensors with greatly enhanced performance through the continuous advances in plasmon resonance techniques such as surface plasmon resonance (SPR) and localized SPR (LSPR)-based refractive index sensing, SPR imaging (SPRi), and surface-enhanced Raman scattering (SERS). Meanwhile, microfluidic integration promotes multiplexing opportunities for the plasmonic biosensors in the simultaneous detection of multiple analytes. Particularly, different types of microfluidic-integrated plasmonic biosensor systems based on versatile patterned plasmonic nanostructured arrays were reviewed comprehensively, including their methods and relevant typical works. The microfluidics-based plasmonic biosensors provide a high-throughput platform for the biochemical molecular analysis with the advantages such as ultra-high sensitivity, label-free, and real time performance; thus, they continue to benefit the existing and emerging applications of biomedical studies, chemical analyses, and point-of-care diagnostics.

Periodic arrays of plasmonic crossed-bowtie nanostructures interspaced with plasmonic nanocrosses for highly sensitive LSPR based chemical and biological sensing.

In this paper, we present novel localized surface plasmon resonance (LSPR) sensors based on periodic arrays of gold crossed-bowtie nanostructures interspaced with gold nanocross pillars. Finite difference time domain (FDTD) numerical simulations were carried out to model bulk sensors as well as localized sensors based on the plasmonic nanostructures being proposed. The geometrical parameters of the plasmonic nanostructures are varied to obtain the best possible sensing performance in terms of sensitivity and figure of merit. A very high bulk sensitivity of 1753 nm per unit change in refractive index (nm RIU−1), with a figure of merit for bulk sensing (FOMbulk) of 3.65 RIU−1, is obtained for these plasmonic nanostructures. This value of bulk sensitivity is higher in comparison to previously proposed LSPR sensors based on plasmonic nanopillars and nanocrosses. Moreover, the optimized LSPR sensors being proposed in this paper provide maximum sensitivity of localized refractive index sensing of 70 nm/nm with a FOMlocalized of 0.33 nm−1. This sensitivity of localized refractive index sensing is the highest reported thus far in comparison with previously reported LSPR sensors. It is also demonstrated that the operating resonance wavelengths of these LSPR sensors can be controllably tuned for specific applications by changing the dimensions of the plasmonic nanostructures.

Inch-Scale Ball-in-Bowl Plasmonic Nanostructure Arrays for Polarization-Independent Second-Harmonic Generation.

Second-harmonic generation (SHG) in plasmonic nanostructures has been investigated for decades due to their wide applications in photonic circuit, quantum optics and biosensing. Development of large-scale, uniform, and efficient plasmonic nanostructure system with tunable modes is desirable for their feasible utilizations. Herein, we design an efficient inch-scale SHG source by a solution-processed method instead of traditional high-cost processes. By assembling the gold nanoparticles with the porous anodic alumina templates, multiresonance in both visible and near-infrared regions can be achieved in hexagonal plasmonic nanostructure arrays, which provide strong electric field enhancement at the gap region. Polarization-independence SHG radiation has been realized owing to the in-plane isotropic characteristic of assembled unit. The tilt-angle dependent and angle-resolved measurement showed that wide-angle nonlinear response is achieved in our device because of the gap geometry of ball-in-bowl nanostructure with nonlinear emission electric dipoles distributed on the concave surface, which makes it competitive in practical applications. Our progress not only makes it possible to produce uniform inch-scale nonlinear arrays through low-cost solution process; and also advances the understanding of the SHG radiation in plasmonic nanostructures.

Au Nanohole–Nanodisk Hybrid Array for Plasmonic Sensing

The phenomenon of extraordinary light transmission through sub‐wavelength‐sized holes in noble metal films has attracted significant attention due to its potential applications in optical filters and plasmonic sensors. Herein, an Au nanohole–nanodisk hybrid array, which allows controllable extraordinary light transmission, is presented to detect the target analytes. A 3D electromagnetic simulation proves that the proposed plasmonic nanostructure array with its constant geometry can vary the light transmittance by altering the refractive index of the surrounding medium. As the refractive‐index‐dependent plasmon coupling between the Au nanohole and nanodisk can drastically enhance the light transmission, the Au nanohole–nanodisk hybrid array can be utilized as a sensitive and feasible plasmonic sensor.

Resist-free nanoimprinting on optical fibers for plasmonic optrodes

Nanostructure patterning on optical fibers enables miniaturized optrodes for photonic and plasmonic applications. Here we report a direct nanoimprint technique to produce high-quality nanostructure arrays on optical fiber endfaces. It has only one single step: imprinting optical fiber tips against a mold with nanostructures at the elevated temperature. This new method abandons resist used in traditional fiber-imprinting methods. Hundreds of fibers can be shaped simultaneously with one mold within minutes. The imprinted nanostructure arrays on optical fibers are transformed into plasmonic optrodes through metal deposition. Variation of imprint depths and mold patterns allows tailoring of the plasmonic resonances of these nanostructure arrays for high-performance refractometric sensing and on-fiber polarization. The sensitivity of 690 nm/RIU and figure of merit of 50 are both among the highest values for similar plasmonic nanostructure arrays. This resist-free nanoimprint paves the way towards a low-cost and high-throughput realization of plasmonic optrodes and their wide applications.

Plasmonic-enhanced microcrystalline silicon solar cells

This paper describes the enhanced performance of the microcrystalline silicon (µc-Si) thin-film solar cells due to the incorporation of plasmonic nanostructures. Finite-difference time-domain numerical modeling is used to calculate the optical properties of the solar cells such as the absorption and the short-circuit current density ( J s c ). In this paper, two-dimensional(2D) periodic arrays of various geometries of plasmonic nanostructures such as nano-rings, nano-discs, nano-hemispheres, and nano-cubes are employed on the back side of the solar cells to increase the absorption for the longer wavelengths of the incident light, where most of the photons remain unharvested due to extremely low absorption coefficients of µc-Si material. These plasmonic nanostructures are compared in terms of solar cell performance, and it is found that the 2D periodic arrays of nano-rings show significant absorption enhancement at multiple wavelengths, thereby leading to a substantial enhancement in the J s c . An enhancement of 35% in the J s c is obtained when a 2D periodic array of plasmonic nano-rings is present on the back side of the solar cell, which is higher than that of the µc-Si solar cells having arrays of plasmonic nanostructures of other geometries (i.e., nano-discs, nano-cubes, nano-hemispheres). It is observed that the enhancement in the absorption is attributed to the enhanced electromagnetic fields in the active layer due to several localized surface plasmon modes that are excited in the plasmonic nanostructures at different wavelengths. Moreover, the effect of the thickness of the spacer layer (the layer between the metal back-reflector and plasmonic nanostructure arrays) on the performance of different plasmonic solar cells is examined.

Tailoring Spin Angular Momentum of Light: Design Principles for Plasmonic Nanostructures

Spin angular momentum (SAM), a fundamental property of light, is associated with the right-hand and left-hand circular polarizations. It has never been trivial to engineer a light beam with desired SAM, and especially at the frequency regime other than the visible region. A widely used approach is to build periodic arrays of plasmonic nanostructures that host two orthogonal dipole resonances. As the unit cell, its structure design is crucial, but the design principle remains obscure. We present a model of two orthogonal resonant Lorentz dipoles to quantitatively describe the creation of SAM in such plasmonic quarter-wave plates. The equal amplitude and $\ensuremath{\pi}/2$ phase difference are essential. The requirements can be achieved by structure modulation and, in addition, the amplitude can be manipulated by varying the polarization angle of incident waves. In practice, the resonant frequency difference of two dipoles $\mathrm{\ensuremath{\Delta}}\ensuremath{\omega}=|{\ensuremath{\omega}}_{A}\ensuremath{-}{\ensuremath{\omega}}_{B}|$, and their damping rate ${\ensuremath{\kappa}}_{A}$ and ${\ensuremath{\kappa}}_{B}$, should meet a basic criterion, such as $\mathrm{\ensuremath{\Delta}}\ensuremath{\omega}\ensuremath{\geqslant}\sqrt{{\ensuremath{\kappa}}_{A}{\ensuremath{\kappa}}_{B}}$. As an illustration, we design a cross-shaped circular polarization convertor, and show its structure and incident angle optimization. We find the optimal working frequency ${\ensuremath{\omega}}_{\mathrm{opt}}$ is roughly equal to $\sqrt{{\ensuremath{\omega}}_{A}{\ensuremath{\omega}}_{B}}$ at the critical condition $\mathrm{\ensuremath{\Delta}}\ensuremath{\omega}=\sqrt{{\ensuremath{\kappa}}_{A}{\ensuremath{\kappa}}_{B}}$. Our results provide good guidance on the design of SAM-enabled plasmonic devices for versatile applications.

Electrophoretic Deposition of WS2 Flakes on Nanoholes Arrays-Role of Used Suspension Medium.

Here we optimized the electrophoretic deposition process for the fabrication of WS2 plasmonic nanohole integrated structures. We showed how the conditions used for site-selective deposition influenced the properties of the deposited flakes. In particular, we investigated the effect of different suspension buffers used during the deposition both in the efficiency of the process and in the stability of WS2 flakes, which were deposited on an ordered arrays of plasmonic nanostructures. We observed that a proper buffer can significantly facilitate the deposition process, keeping the material stable with respect to oxidation and contamination. Moreover, the integrated plasmonic structures that can be prepared with this process can be applied to enhanced spectroscopies and for the preparation of 2D nanopores.

A review of 2D and 3D plasmonic nanostructure array patterns: fabrication, light management and sensing applications

Abstract This review article discusses progress in surface plasmon resonance (SPR) of two-dimensional (2D) and three-dimensional (3D) chip-based nanostructure array patterns. Recent advancements in fabrication techniques for nano-arrays have endowed researchers with tools to explore a material’s plasmonic optical properties. In this review, fabrication techniques including electron-beam lithography, focused-ion lithography, dip-pen lithography, laser interference lithography, nanosphere lithography, nanoimprint lithography, and anodic aluminum oxide (AAO) template-based lithography are introduced and discussed. Nano-arrays have gained increased attention because of their optical property dependency (light-matter interactions) on size, shape, and periodicity. In particular, nano-array architectures can be tailored to produce and tune plasmonic modes such as localized surface plasmon resonance (LSPR), surface plasmon polariton (SPP), extraordinary transmission, surface lattice resonance (SLR), Fano resonance, plasmonic whispering-gallery modes (WGMs), and plasmonic gap mode. Thus, light management (absorption, scattering, transmission, and guided wave propagation), as well as electromagnetic (EM) field enhancement, can be controlled by rational design and fabrication of plasmonic nano-arrays. Because of their optical properties, these plasmonic modes can be utilized for designing plasmonic sensors and surface-enhanced Raman scattering (SERS) sensors.

Planar Aperiodic Arrays as Metasurfaces for Optical Near-Field Patterning

Plasmonic metasurfaces have spawned the field of flat optics using nanostructured planar metallic or dielectric surfaces that can replace bulky optical elements and enhance the capabilities of traditional far-field optics. Furthermore, the potential of flat optics can go far beyond far-field modulation and can be exploited for functionality in the near-field itself. Here, we design metasurfaces based on aperiodic arrays of plasmonic Au nanostructures for tailoring the optical near-field in the visible and near-infrared spectral range. The basic element of the arrays is a rhomboid that is modulated in size, orientation, and position to achieve the desired functionality of the micron-size metasurface structure. Using two-photon-photoluminescence as a tool to probe the near-field profiles in the plane of the metasurfaces, we demonstrate the molding of light into different near-field intensity patterns and active pattern control via the far-field illumination. Finite element method simulations reveal that the near-field modulation occurs via a combination of the plasmonic resonances of the rhomboids and field enhancement in the nanoscale gaps in between the elements. This approach enables optical elements that can switch the near-field distribution across the metasurface via wavelength and polarization of the incident far-field light and provides pathways for light matter interaction in integrated devices.

In-Plane Surface Lattice and Higher Order Resonances in Self-Assembled Plasmonic Monolayers: From Substrate-Supported to Free-Standing Thin Films.

Periodic arrays of plasmonic nanostructures are able to strongly confine light at the nanometer scale because of surface lattice resonances. These resonances are the result of electromagnetic coupling between single-particle localized surface plasmon resonances and Bragg resonances of the periodic lattice. Here, we investigate the effect of a finite size refractive index environment on the formation of surface lattice resonances by increasing the thickness of a polymer coating in nanometer-scale increments. Wet-chemically synthesized, spherical silver and gold nanoparticles with soft hydrogel shells are self-assembled into macroscopic, hexagonally ordered arrays on glass substrates using an interface-assisted approach. The resulting periodic plasmonic monolayers are subsequently coated by a polymer matching closely the refractive index of the glass support. The optical response of the plasmonic arrays is studied using far-field extinction spectroscopy and supported by numerical simulations. We show the formation of surface lattice resonances as well as higher order resonances in finite thickness polymer coatings. The resonance positions are determined by the interparticle spacing as well as the plasmonic material. Additionally, we demonstrate that a coating thickness of 450 nm is sufficient to support strong in-plane surface lattice resonances. This enables us to prepare macroscopic, free-standing polymer films with embedded plasmonic nanoparticle arrays, which feature strong surface lattice resonances.

Extraordinary optical transmission properties of a novel Bi-layered plasmonic nanostructure array

The optical transmission properties of a novel bi-layer plasmonic nanostructure array (BPNA), consisting of an array of gold nanoholes, glass and an array of gold nanodisks, was investigated by the finite element method. A well-defined localized surface plasmon (LSP) resonance peak appeared in the transmission spectra due to the coupling between the LSP of the metal nanoholes and the LSP of the nanodisks. The position and the intensity of the coupled LSP resonance peak depended strongly on the distance between the nanohole and the nanodisk arrays, the diameters of the arrays and the thickness of the nanohole or nanodisk arrays. The coupled LSP resonance peak exhibited a higher figure of merit compared to that for either the nanohole array or the nanodisk array. Results indicated that the bi-layer nanodevice was a highly sensitive detector for tunable plasmas, and should aid in better understanding of the mechanisms for extraordinary optical transmission phenomena.

Manifestation of Planar and Bulk Chirality Mixture in Plasmonic Λ-Shaped Nanostructures Caused by Symmetry Breaking Defects

We report on the coexistence of planar and bulk chiral effects in plasmonic Λ-shaped nanostructure arrays arising from symmetry breaking defects. The manifestation of bi- (2D) and three-dimensional (3D) chiral effects are revealed by means of polarization tomography and confirmed by symmetry considerations of the experimental Jones matrix. Notably, investigating the antisymmetric and symmetric parts of the Jones matrix points out the contribution of 2D and 3D chirality in the polarization conversion induced by the system whose eigenpolarizations attest to the coexistence of planar and bulk chirality. Furthermore, we introduce a generalization of the microscopic model of Kuhn, yielding to a physical picture of the origins of the observed planar chirality, circular birefringence, and dichroism, theoretically prohibited in symmetric Λ-shaped nanostructures.

Fabrication of Periodic Gold Nanocup Arrays Using Colloidal Lithography.

Within recent years, the field of plasmonics has exploded as researchers have demonstrated exciting applications related to chemical and optical sensing in combination with new nanofabrication techniques. A plasmon is a quantum of charge density oscillation that lends nanoscale metals such as gold and silver unique optical properties. In particular, gold and silver nanoparticles exhibit localized surface plasmon resonances-collective charge density oscillations on the surface of the nanoparticle-in the visible spectrum. Here, we focus on the fabrication of periodic arrays of anisotropic plasmonic nanostructures. These half-shell (or nanocup) structures can exhibit additional unique light-bending and polarization-dependent optical properties that simple isotropic nanostructures cannot. Researchers are interested in the fabrication of periodic arrays of nanocups for a wide variety of applications such as low-cost optical devices, surface-enhanced Raman scattering, and tamper indication. We present a scalable technique based on colloidal lithography in which it is possible to easily fabricate large periodic arrays of nanocups using spin-coating and self-assembled commercially available polymeric nanospheres. Electron microscopy and optical spectroscopy from the visible to near-infrared (near-IR) was performed to confirm successful nanocup fabrication. We conclude with a demonstration of the transfer of nanocups to a flexible, conformal adhesive film.

Reversible Tuning of Visible Wavelength Surface Lattice Resonances in Self‐Assembled Hybrid Monolayers

Periodic arrays of plasmonic nanostructures can support surface lattice resonances emerging from coupling between localized and diffractive modes. This allows the confinement of light at the nanometer scale with significantly increased resonance lifetimes as compared to those of purely localized modes. Here, we demonstrate that self‐assembly of plasmonic hybrid nanoparticles allows the simple and fast fabrication of periodic plasmonic monolayers featuring macroscopic dimensions and easily controllable lattice spacings. Electromagnetic coupling between diffractive and localized modes is significantly enhanced when the arrays are embedded in a homogeneous refractive index environment. This is realized through spin‐coating of a polymer film on top of the colloidal monolayer. Narrow surface lattice resonances are detected by far‐field extinction spectroscopy while optical microscopy reveals a homogeneous coupling strength on cm‐sized substrates. The surface lattice resonance position is changed by manipulation of the refractive index of the polymer film through the immersion into different organic solvents. Capitalizing on the thermoresponsive behavior of the polymer film we modulate the surface lattice resonance by temperature in a fully reversible, dynamic manner. The findings demonstrate the potential of colloidal self‐assembly as a bottom‐up approach for the fabrication of future nanophotonic devices.

Nanoimprint methods for the fabrication of macroscopic plasmonically active metal nanostructures

In this article, we present a refined nanostructuring method, lift-off nanoimprint lithography (LO-NIL), which allows the deposition of high-quality metal nanostructures due to a bilayer resist process and compare it to nano-transfer printing (nTP), a purely additive metal printing technique. LO-NIL and nTP are used as accurate methods for the fabrication of ordered plasmonic metal nanostructure arrays on semiconducting substrates over large areas using the example of gold nanodisks on silicon. The possibility of feature size adjustment in LO-NIL during the fabrication process is especially useful for tuning plasmonic resonance peaks between the visible and the mid-infrared range as well as fine-tuning of these resonances. In UV-VIS-NIR spectroscopic measurements, a significant blueshift in the plasmonic resonance was found for nTP samples compared to the ones fabricated with the lift-off technique. It was concluded that this shift originates from a metal/substrate interface roughness resulting in a change in the dielectric properties of this layer. This finding was verified with finite difference time-domain simulations where a similar trend was found for a model with an assumed thin air gap in this interface. In cyclic voltammetry measurements under illumination, a reduced overpotential by almost 400 mV for CO2 reduction and hydrogen evolution was found for LO-NIL samples.