Plasmonic Coatings Research Articles

Tuning the plasmonic resonance in TiN refractory metal

Plasmonic coatings can absorb electromagnetic radiation from visible to far-infrared spectrum for the better performance of solar panels and energy saving smart windows. For these applications, it is important for these coatings to be as thin as possible and grown at lower temperatures on arbitrary substrates like glass, silicon, or flexible polymers. Here, we tune and investigate the plasmonic resonance of titanium nitride thin films in lower thicknesses regime varying from ~ 20 to 60 nm. High-quality crystalline thin films of route-mean-square roughness less than ~ 0.5 nm were grown on a glass substrate at temperature of ~ 200 °C with bias voltage of − 60 V using cathodic vacuum arc deposition. A local surface-enhanced-plasmonic-resonance was observed between 400 and 500 nm, which further shows a blueshift in plasmonic frequency in thicker films due to the increase in the carrier mobility. These results were combined with finite-difference-time-domain numerical analysis to understand the role of thicknesses and stoichiometry on the broadening of electromagnetic absorption.

Plasmonic black coatings with broadband absorption for space applications

Stray-light reduction is critical for the operation of optical components in space. Here, we report on the testing of high performance plasmonic broadband absorbing black coatings for space applications fabricated by metastable atomic layer deposition (MS-ALD). For this purpose, humidity testing, thermal cycling, exposure to atomic oxygen, and adhesion testing were used as testing methods. The results show that the films with thickness greater than 9 μm are able to withstand the humidity tests, thermal cycling, and exposure to atomic oxygen without significant loss of their broadband absorption. However, it was also observed that the adhesion of the films has not yet been sufficient to meet the requirements posed by the space environment. Therefore, the authors conclude that further fine-tuning of the films with respect to increasing adhesion is required to make the films suitable for space applications. Therefore, the authors propose to investigate the coating of the MS-ALD films with high refractive index coatings.

Exploring the Bottom-Up Growth of Anisotropic Gold Nanoparticles from Substrate-Bound Seeds in Microfluidic Reactors.

We developed an unconventional seed-mediated in situ synthetic method, whereby gold nanostars are formed directly on the internal walls of microfluidic reactors. The dense plasmonic substrate coatings were grown in microfluidic channels with different geometries to elucidate the impacts of flow rate and profile on reagent consumption, product morphology, and density. Nanostar growth was found to occur in the flow-limited regime and our results highlight the possibility of creating shape gradients or incorporating multiple morphologies in the same microreactor, which is challenging to achieve with traditional self-assembly. The plasmonic-microfluidic platforms developed herein have implications for a broad range of applications, including cell culture/sorting, catalysis, sensing, and drug/gene delivery.

High performance refractive index SPR sensor modeling employing graphene tri sheets

This article illustrates a graphene tri sheets based surface plasmon resonance (SPR) biosensor. The exciting configuration consists of Gold (Au), graphene, prism (SF11 glass) and sensing medium. The angular interrogation scheme is basically utilized owing to inspect the light reflection from the sensor. For sake of the augmentation of sensor sensitivity (S), signal to noise ratio (SNR), quality factor (QF), first of all, the impact of adding graphene layer is investigated and then the number of graphene layers are optimized to tri layers. According to that tri sheets, the SPR curves are sketched and comparison of sensor sensitivity, SNR, the quality factor is made among the existing works. It is audited that an extraordinary improvement of sensitivity to 121.67° RIU−1. The most effective graphene layers states with improved SNR of 2.21 and QF of 36.87 RIU−1 respect conventional SPR sensor. After then, the electric field intensity on implanting graphene sheet is analyzed by incorporating the finite difference time domain (FDTD) method by applying the Opti FDTD multiphysics commercial software environment. The proposed design bears the advantages of high sensitivity, QF and SNR comparing with the existing sensors along with simple stricture, no need of plasmonic coatings of other dielectrics, compactness, light weight, real time fabrication flexibility due to avoid multi materials optical structure.

Thermal annealing induced evolution of morphological, structural, optical and photocatalytic properties of Ag-TiO2 nanocomposite thin films

Plasmonic nanocomposite coatings are important for applications ranging from solar photovoltaics to environmental remediation. Plasmonic Ag-TiO2 nanocomposites were fabricated by atom beam sputtering. Morphological and microstructural variations in Ag-TiO2 nanocomposite thin film upon thermal annealing were investigated. FESEM studies revealed nanoparticles which grew in size and also aggregated forming nanostructures with shape anisotropy on surface upon annealing. The nanocomposite nature of the film with Ag and TiO2 nanocrystals was confirmed by X-ray diffraction. UV-Vis DRS spectra showed significant improvement in absorbance due to the plasmonic properties of aggregated Ag nanostructures formed and improvement in the crystallinity of the film upon annealing. Ag-TiO2 nanocomposite coatings were used for solar light induced photocatalytic degradation of methylene blue in water. The Ag-TiO2 coating annealed at 600 °C was found to be the most efficient photocatalyst degrading 2.5 μM MB in water in only 20 min, which is exciting for practical applications. The tentative mechanism underlying the observed enhancement in the photocatalytic efficiency of Ag-TiO2 coating upon annealing is proposed.

Empowering Electroless Plating to Produce Silver Nanoparticle Films for DNA Biosensing Using Localized Surface Plasmon Resonance Spectroscopy.

To facilitate the implementation of biosensors based on the localized surface plasmon resonance (LSPR) of metal nanostructures, there is a great need for cost-efficient, flexible, and tunable methods for producing plasmonic coatings. Due to its simplicity and excellent conformity, electroless plating (EP) is well suited for this task. However, it is traditionally optimized to produce continuous metal films, which cannot be employed in LSPR sensors. Here, we outline the development of an EP strategy for depositing island-like silver nanoparticle (NP) films on glass with distinct LSPR bands. The fully wet-chemical process only employs standard chemicals and proceeds within minutes at room temperature. The key step for producing spread-out NP films is an accelerated ripening of the silver seed layer in diluted hydrochloric acid, which reduces the nucleation density during plating. The reaction kinetics and mechanisms are investigated with scanning (transmission) electron microscopy (SEM/STEM), X-ray photoelectron spectroscopy (XPS), and UV-vis spectroscopy, with the latter enabling a convenient live monitoring of the deposition, allowing its termination at a stage of desired optical properties. The sensing capabilities of chemically deposited NP films as LSPR transducers are exemplified in DNA biosensing. To this end, a sensing interface is prepared using layer-by-layer (LbL) buildup of polyelectrolytes (PE), followed by adsorption and covalent immobilization of ssDNA. The obtained LSPR transducers demonstrate robustness and selectivity in sensing experiments with binding complementary and unrelated DNA strands.

Ion beam engineering of morphological, structural, optical and photocatalytic properties of Ag-TiO2-PVA nanocomposite thin film

Development of plasmonic nanocomposite coatings with tunable optical and photocatalytic properties is important for diverse technological applications. In this paper, we report modifications in the microstructural, optical and photocatalytic properties of Ag-TiO2-PVA nanocomposite thin film by 8 MeV Si3+ ion irradiation. Ag-TiO2-PVA nanocomposite thin films on silica glass were prepared by a combination of sol-gel method and spin coating. Ion irradiation induced morphological evolution of Ag-TiO2-PVA thin film was studied by atomic force microscopy and field emission scanning electron microscopy, which revealed interesting changes in the size distribution of nanostructures with increasing ion fluence. Ion irradiation of the Ag-TiO2-PVA thin film resulted in the emergence of SPR peak of Ag nanoparticles at 456 nm, which shifted to 446 nm along with enhancement in intensity as the ion fluence was increased. Significant enhancement in the photocatalytic efficiency of Ag-TiO2-PVA nanocomposite thin film for degradation of methylene blue was observed upon ion irradiation at 1 × 1013 ions/cm2. The origins of microstructural, morphological, optical and plasmonic modifications and enhancement in the photocatalytic efficiency of Ag-TiO2-PVA nanocomposite thin films have been discussed.

Novel design of plasmonic and dielectric antireflection coatings to enhance the efficiency of perovskite solar cells

Recently, nanostructured plasmonic antireflection coatings emerge as a solution to minimize reflection in solar cells over a wideband. However, metals have large light absorption coefficient, making this solution non-reliable for efficient large-scale production. On the other hand, all dielectric antireflection coatings are considered as promising alternative due to the lower losses and easier assembly, especially for third generation photovoltaics such as perovskite solar cells. Herein, we report a first principles methodology for selecting and comparing optimally nanostructured antireflective coatings for enhancing the efficiency of perovskite solar cells based on Mie theory. The first part of the method includes studying absorption and scattering cross sections of five nanostructures and identifying the role of magnetic and electric dipoles. Accordingly, dimensions of each nanostructure that maximizes light coupling to the solar cell active layer was identified. The second part comprises the study of the coupling effect between closed nanostructures. Using three-dimensional finite element method optical and electrical model, periodicity and dimensions of the proposed nanostructures with the highest generated photocurrent were identified. The results showed 15% enhancement in short circuit current (Jsc) over the entire wavelength band, and up to 27% in narrow band spectrum compared to planar perovskite solar cells.

Hot Electron Harvesting via Photoelectric Ejection and Photothermal Heat Relaxation in Hotspots-Enriched Plasmonic/Photonic Disordered Nanocomposites

The ability of plasmonic nanostructures to harvest photons beyond the traditional band-to-band photovoltaic conversion of semiconductors has stimulated intensive research activities in hot electron. As an emerging strategy for energy-harvesting, photodetection and photocatalysis, realization of broadband and efficient plasmonic absorption with easily constructed metal-semconductor (M-S) nanosystems is essential for improving its photoelectric efficiency, while minimizing the cost and complexity of fabrication. Here, we report an approach for near-infrared (NIR) photodetection by combining the randomly and densely packed photonic nanostructures with ultrathin plasmonic coatings. Relying on the Au covered disordered silicon nanoholes (SiNHs) M-S platform, the efficient plasmonic absorption, strong field localization and together with random nature facilitate the broadband photon-energy conversion from both photoelectric hot electron ejection and photothermal hot electron relaxation. Spectral- and time-resol...

Thermal graphene metamaterials and epsilon-near-zero high temperature plasmonics

The key feature of a thermophotovoltaic (TPV) emitter is the enhancement of thermal emission corresponding to energies just above the bandgap of the absorbing photovoltaic cell and simultaneous suppression of thermal emission below the bandgap. We show here that a single layer plasmonic coating can perform this task with high efficiency. Our key design principle involves tuning the epsilon-near-zero frequency (plasma frequency) of the metal acting as a thermal emitter to the electronic bandgap of the semiconducting cell. This approach utilizes the change in the reflectivity of a metal near its plasma frequency (epsilon-near-zero frequency) to lead to spectrally selective thermal emission, and can be adapted to large area coatings using high temperature plasmonic materials. We provide a detailed analysis of the spectral and angular performance of high temperature plasmonic coatings as TPV emitters. We show the potential of such high temperature plasmonic thermal emitter coatings (p-TECs) for narrowband near-field thermal emission. We also show the enhancement of near-surface energy density in graphene-multilayer thermal metamaterials due to a topological transition at an effective epsilon-near-zero frequency. This opens up spectrally selective thermal emission from graphene multilayers in the infrared frequency regime. Our design paves the way for the development of single layer p-TECs and graphene multilayers for spectrally selective radiative heat transfer applications.

Plasmonic and silicon spherical nanoparticle antireflective coatings.

Over the last decade, plasmonic antireflecting nanostructures have been extensively studied to be utilized in various optical and optoelectronic systems such as lenses, solar cells, photodetectors, and others. The growing interest to all-dielectric photonics as an alternative optical technology along with plasmonics motivates us to compare antireflective properties of plasmonic and all-dielectric nanoparticle coatings based on silver and crystalline silicon respectively. Our simulation results for spherical nanoparticles array on top of amorphous silicon show that both silicon and silver coatings demonstrate strong antireflective properties in the visible spectral range. For the first time, we show that zero reflectance from the structure with silicon coatings originates from the destructive interference of electric- and magnetic-dipole responses of nanoparticle array with the wave reflected from the substrate, and we refer to this reflection suppression as substrate-mediated Kerker effect. We theoretically compare the silicon and silver coating effectiveness for the thin-film photovoltaic applications. Silver nanoparticles can be more efficient, enabling up to 30% increase of the overall absorbance in semiconductor layer. Nevertheless, silicon coatings allow up to 64% absorbance increase in the narrow band spectral range because of the substrate-mediated Kerker effect, and band position can be effectively tuned by varying the nanoparticles sizes.

Role of the spacer layer in plasmonic antireflection coatings comprised of gold or silver nanoparticles

Metal nanoparticles (NPs) can increase the absorption of light within semiconductors and hence improve the efficiency of solar cells. We experimentally investigate the effect that gold and silver NPs have on the reflectance of silicon wafers. The NPs are fabricated using the low cost, large area technique of thermal dewetting. We show that a dielectric spacer layer between the NPs and the semiconductor is required to achieve a net reduction of reflection. Furthermore, the optimum thickness of the spacer layer is found to be independent of NP size and metal type.

Effect of EVA Encapsulation on Antireflection Properties of Mie Nanoscatterers for c-Si Solar Cells

Dielectric nanoparticle arrays have been proposed as antireflection coatings and light-trapping schemes for thin-film c-Si solar cells. However, practical aspects about the integration of these nanostructures with solar modules have yet to be investigated. In this paper, we study the effect of ethylene vinyl acetate (EVA) encapsulation on the optical properties of dielectric nanoparticles placed on top of c-Si substrates. We experimentally show that Si nanoparticle Mie coatings encapsulated in an EVA layer yield ultralow reflectivity over the entire 300-1000-nm spectral range. The AM1.5-weighted average reflectivity of the Mie coating is as low as 1.5%, which is comparable with that of a standard alkaline texture used for c-Si solar cells. TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticle Mie coatings also yield similar results. Mie coatings are thus valid substitutes of standard textures for ultrathin devices. We also study the case of plasmonic nanoparticle coatings for c-Si solar cells. We find that they are not suited for c-Si cells when EVA encapsulation is used.

RCS computations of targets with plasmonic coatings

As far as RADAR Cross Section (RCS) computations are concerned, metamaterial coating modeling issues lead to cases of millions of unknowns for targets greater than the wavelength. For computational limiting reasons, details of the coating cannot be meshed, even if they play a key role like in metamaterial design. Equivalent boundary conditions or effective medium approximation are then necessary. In this paper we consider spheres and cone-spheres with plasmonic coatings. Exact and approximated RCS computations are compared over a broad range of microwave frequencies. In the last section, we eventually point out the relevance of full-metallic grooved coatings in designing calibration objects exhibiting low RCS without the use of conventional RADAR Absorbing Materials.

Near‐Infrared Spectrally Selective Plasmonic Electrochromic Thin Films

A plasmonic electrochromic effect in which electrochemical doping reversibly modulates near-infrared surface plasmon absorption of aluminium-doped zinc oxide and tin-doped indium oxide nanocrystals is reported. Optical performance, switching kinetics, and cycling durability point to high-performance NIR selective plasmonic electrochromic coatings based on earth-abundant materials.

Enhanced photocurrent in crystalline silicon solar cells by hybrid plasmonic antireflection coatings

Photocurrent enhancement induced by plasmonic light trapping is of great interest for photovoltaics. We design and demonstrate hybrid plasmonic antireflection coatings as an efficient light trapping strategy for broadband absorption and photocurrent enhancement in crystalline silicon solar cells. Gold nanoparticles of size ranging from 15 to 150 nm are embedded in standard SiNx antireflection coatings with a thickness of 90 nm. Through optimizing the location of tailored nanoparticles within the SiNx layer, both light scattering enhancement and near-field light concentration can be harnessed. A maximum increase of 6.3% in photocurrent is achieved for textured multi-crystalline Si solar cells with the optimum configuration.

Comparison of frequency responses of cloaking devices under nonmonochromatic illumination

Plasmonic coatings have been proposed as a robust method to suppress the scattering signature of conventional dielectric objects, typically by surrounding a given object of moderate size with an isotropic, homogeneous, dispersive material that has a low or negative permittivity. In contrast to transformation-based cloaking devices, where highly anisotropic inhomogeneous materials achieve invisibility by electromagnetically isolating a certain region of space, plasmonic cloaks operate under the principle of scattering cancellation and usually allow field energy to enter the device's core. So far, plasmonic devices have been mostly examined using single-frequency, plane-wave excitations. In this work, the performance of such plasmonic cloaks when illuminated by more realistic, broadband nonmonochromatic pulses is investigated and compared with other cloaking mechanisms. The two-dimensional total-field scattered-field method is used within the finite-difference time-domain dispersive numerical technique in order to simulate time domain effects when temporally Gaussian pulses are launched toward cylindrical moderately-sized dielectric objects which are covered with appropriate plasmonic coatings. The results are compared to the performance of transformation-based cloaks, finding that the plasmonic cloaks may suppress scattering more effectively over a wider frequency range.

Optimization of Plasmonic Enhancement of Fluorescence on Plastic Substrates

In this work, we report on the uniform deposition of tailored plasmonic coatings on polymer substrates and on the distance dependence of the plasmonic enhancement of a fluorescent dye. Silver, gold, and silver/gold alloy nanoparticles (NPs) with a range of diameters were synthesized using chemical techniques and characterized using UV-vis absorption spectroscopy, transmission electron microscopy (TEM), and atomic force microscopy (AFM). Reproducible polyelectrolyte (PEL) layers, which were deposited on plastic microwell plates using a layer-by-layer technique, served as both a stable and uniform substrate for deposition of the NPs as well as providing spacer layers of known thickness between the NPs and the fluorescent dye. A maximum enhancement factor of approximately 11 was measured for 60 nm diameter pure silver NPs, for a dye-NP separation of approximately 3 nm. A shift in the localized surface plasmon resonance (LSPR) wavelength as a function of the effective refractive index of the PEL layers was also observed, and the measured shifts show a similar trend with theoretical predictions. This work will contribute toward the rational design of optical biochip platforms based on plasmon-enhanced fluorescence.

Erratum: Achieving transparency with plasmonic and metamaterial coatings [Phys. Rev. E,72, 016623 (2005)

Received 22 December 2005DOI:https://doi.org/10.1103/PhysRevE.73.019906©2006 American Physical Society

Achieving transparency with plasmonic and metamaterial coatings

The possibility of using plasmonic and metamaterial covers to drastically reduce the total scattering cross section of spherical and cylindrical objects is discussed. While it is intuitively expected that increasing the physical size of an object may lead to an increase in its overall scattering cross section, here we see how a proper design of these lossless metamaterial covers near their plasma resonance may induce a dramatic drop in the scattering cross section, making these objects nearly "invisible" or "transparent" to an outside observer--a phenomenon with obvious applications for low-observability and noninvasive probe design. Physical insights into this phenomenon and some numerical results are provided.