Plasmonic Layer Research Articles

Ultra-sensitivity of surface plasmon resonance sensor using halide perovskite FASnI3 and 2D materials on Cu thin films

This paper studies a novel surface plasmon resonance (SPR) biosensor using a BK7 glass prism, a copper (Cu) metal plasmonic layer, which combine a halide perovskite (FASnI3) with two-dimensional (2D) materials such as phosphorus black, graphene and TMDC (MoS2, MoSe2, WS2, WSe2) for the detection of breast cancer cells. We have optimized the thickness of each layer in order to obtain maximum sensitivity. A numerical study mainly uses the transfer matrix principle, while the attenuation total reflection method involves examining the reflection properties. The evaluation of SPR biosensor configurations serves to obtain optimal performance. The simulation results indicate that the integration of halide perovskite (FASnI3) and 2D materials into the BK7/Cu/medium sensing structure significantly improves the sensitivity and figure of merit (ZT). The outstanding results in terms of sensor performance characteristics are observed in the BK7/Cu (48 nm)/FASnI3 (5 nm)/BP (0.53 nm) configuration. The figure of merit and sensitivity estimated at 123.11 RIU−1 and 459.28°/RIU, with a notable improvement of 338.45 %.

Engineering Fano resonances in plasmonic metasurfaces for colorimetric sensing and structural colors

In this paper, we present the design and fabrication of a plasmonic metasurface based on titanium dioxide (TiO2) nanowire arrays integrated with plasmonic layers. The structure is engineered to produce Fano resonances within the visible spectrum, resulting from the coupling of localized surface plasmon resonances, lattice modes, and nanowire's optical modes. Experimentally, we show that by tuning the geometrical features of the metasurface, such as the length, diameter, and period of the nanowires, a high-quality factor single peak can be achieved in the reflection spectra, resulting in vivid structural colors in bright field. To our knowledge, this is the first demonstration of such vivid colors with nanowire arrays in bright field reflections. When characterized by refractive index fluids around the refractive index of water, the plasmonic metasurface also showed great potential for biochemical colorimetric sensing. The best design demonstrated a bulk sensitivity of 183 nm/RIU with high Q resonance features and linear changes in color values using image processing.

Optimization of highly sensitive three-layer photonic crystal fiber sensor based on plasmonic

In this work, a photonic crystal fiber (PCF) refractive index (RI) sensor has been designed and optimized. The RIs range covered by the sensor is from 1.38 to 1.41. The proposed optical sensor has three layers of air holes with 24, 12 and 6 holes in each layer. The geometry parameters of the proposed sensor (the radius of the air holes and the thickness of the plasmonic layer) have been optimized using the Nelder-Mead algorithm and the FEM numerical with the objective of achieving the highest sensitivity. To achieve an optimized structure with minimal sensitivity to fabrication errors, the rotation angle of the hole layers has been analyzed. The results indicate that, due to the specific geometry of the proposed structure, variations in the rotation angle and displacement of the air holes have no significant impact on the outcomes. The results also indicate that the sensor’s maximum amplitude sensitivity (AS), maximum wavelength sensitivity (WS), and figure of merit (FOM) are 10000 (RIU−1), 23000 (nm/RIU) and 131 (RIU−1) respectively. The optimized design provides high sensitivity, a wide diagnostic range for the detection of the analytes’ RIs, and the advantages of a gold plasmonic layer, ensuring high stability in biological environments. This combination results in enhanced performance of the sensor for various applications particularly in biosensing and medical fields. The designed structural geometry also eliminates the effects of tolerances in manufacturing processes which makes the proposed PCF device a very efficient sensor.

Nanosensors Based on Bimetallic Plasmonic Layer and Black Phosphorus: Application to Urine Glucose Detection.

This paper presents a new biosensor design based on the Kretschmann configuration, for the detection of analytes at different refractive indices. Our studied design consists of a TiO2/SiO2 bi-layer sandwiched between a BK7 prism and a bimetallic layer of Ag/Au plasmonic materials, covered by a layer of black phosphorus placed below the analyte-containing detection medium. The different layers of our structure and analyte detection were optimized using the angular interrogation method. High performance was achieved, with a sensitivity of 240 deg/RIU and a quality factor of 34.7 RIU-1. This biosensor can detect analytes with a wide refractive index range between 1.330 and 1.347, such as glucose detection in urine samples using a refractive index variation of 10-3. This capability offers a wide range of applications for biomedical and biochemical detection and selectivity.

Fundamentals and recent developments of free-space optical neural networks

Machine learning with artificial neural networks has recently transformed many scientific fields by introducing new data analysis and information processing techniques. Despite these advancements, efficient implementation of machine learning on conventional computers remains challenging due to speed and power constraints. Optical computing schemes have quickly emerged as the leading candidate for replacing their electronic counterparts as the backbone for artificial neural networks. Some early integrated photonic neural network (IPNN) techniques have already been fast-tracked to industrial technologies. This review article focuses on the next generation of optical neural networks (ONNs), which can perform machine learning algorithms directly in free space. We have aptly named this class of neural network model the free space optical neural network (FSONN). We systematically compare FSONNs, IPNNs, and the traditional machine learning models with regard to their fundamental principles, forward propagation model, and training process. We survey several broad classes of FSONNs and categorize them based on the technology used in their hidden layers. These technologies include 3D printed layers, dielectric and plasmonic metasurface layers, and spatial light modulators. Finally, we summarize the current state of FSONN research and provide a roadmap for its future development.

Mott–Schottky heterostructural TiO2@Ag@AgBr nanohybrids for efficient photocatalytic degradation of Cr (VI) and enhanced on-site SERS detection

In the study, a novel ternary composite TiO2@Ag@AgBr was successfully prepared by surface modification of complete Ag layer and AgBr particles for photocatalytic degradation of representative heavy metal ions Cr (VI) and on-site Surface-enhanced Raman spectroscopy (SERS) detection of the Cr (VI) reduction process. The Mott–Schottky heterojunction contained structure exhibited remarkable photocatalytic ability for heavy metal ions Cr (VI) by tuning the ratio of Ag and AgBr, which could reduce Cr (VI) ions within 30 min and the reaction rate constant is 0.12 min−1. The remarkable photo-reduction performance is attributed to synergistic effect among the various components: the AgBr decorated on the surface of TiO2@Ag could significantly enhance the absorption of visible light and generate numerous photoexcited electrons and holes. Furthermore, the complete Ag layer was constructed on the TiO2 microspheres surface to form heterojunctions in the photocatalytic system by in-situ deposition of AgNO3. Mott–Schottky junctions formed between AgBr/Ag and Ag/TiO2 interface which could extend the charge transfer pathway and facilitate separation of photoexcited electrons and holes. The plasmonic metal layer of nano Ag could generate significant surface plasmon resonance (SPR) effect which not only enhanced the absorption of visible light but also exhibited remarkable SERS effect for probe molecules. And an amazing detection limit of 1 × 10–10 M could be obtained when using crystal violet (CV) as probe molecules. In addition, the SERS substrates exhibited significant linear relationship between concentration and SERS signal intensity which ensures the accuracy of quantitative analysis and monitoring photoreduction process. The substrates have good cycling stability, enabling it to be reused for SERS detection many times. Thus, the excellent photocatalytic and SERS performance of Mott–Schottky hetero-structural TiO2@Ag@AgBr substrates shows great potential toward rapidly photocatalytic removal Cr (VI) ions and SERS on-site detection reduction process of Cr (VI) in waste water, which is of great significance to environmental protection and ecological restoration.

A unique wheel-shaped exposed core LSPR-PCF sensor for dual-peak sensing: Applications in the optical communication bands, M-IR region and biosensing

Photonic Crystal Fibers (PCF) effectiveness in practice decreases if the fabrication of the sensor becomes too complex. Keeping this in mind, we propose a one-of-a-kind wheel shaped PCF sensor with an exposed core containing only three air holes with exceptional sensing features. The sensor is equipped with dual plasmonic layers, Indium Tin Oxide (ITO, 10 % wt) and silver (Ag) with a coating of TiO2 to enhance the sensing capabilities and provide protection against oxidation. The sensor's distinctive configuration enables it to exhibit two distinct peaks within a range of refractive index from 1.32 to 1.38 for y-polarization and from 1.35 to 1.38 for x-polarization. The sensor specifications have been optimized to achieve the maximum levels of wavelength sensitivity (WS) and double peak shift sensitivity (DPSS). The sensor portrays a WS of 50,652 nm/RIU and the highest DPSS ever recorded, measuring 50,000 nm/RIU. Additionally, the sensor exhibits a significantly high scale of amplitude sensitivity (AS) of 1668.34 RIU−1 which is a very remarkable value considering silver as plasmonic material along with an outstanding figure of merit (FOM) of 1017.11 RIU−1. In addition, our sensor is able to manifest resolutions in the order of 10−6, demonstrating a resolution of 5.94 × 10−6 RIU with the deployment of amplitude interrogation method and 1.97 × 10−6 RIU with the wavelength interrogation method. The design spans an extensive spectrum, covering ultraviolet to mid-infrared wavelengths, enabling detection of biomolecules and biochemicals, along with operation in the optical communication band.

Highly sensitive detection of low-concentration sodium chloride solutions based on a gold-coated prism in Kretschmann setup

A gold-coated Kretschmann setup has been constructed and explored as a surface plasmon resonance (SPR) platform, specifically tailored for the detection of low-concentration sodium chloride (NaCl) solutions. The setup employs a BK7 prism coated with a 50 nm gold layer, serving as a plasmonic layer, to induce resonance. This resonance arises from the interplay between light waves and free electrons propagating at the interface of two media. The experimental findings reveal a notable resonance angle shift of 10° when the NaCl concentration is varied from 0 to 2.5 %. Furthermore, angle interrogation provides insightful details about the sensor's response to changes in the refractive index, showcasing a commendable sensitivity of 2400°/RIU, a high level of linearity at 0.9771, and an impressive resolution of 0.217 %. The demonstrated capabilities of this sensor underscore its potential for widespread applications, particularly in the monitoring of salt concentration across diverse domains such as seawater analysis, food processing, and fermentation processes. The robust performance and precision of this proposed sensor position it as a valuable tool with promising prospects for addressing the needs of various industries dependent on accurate salt concentration measurements.

Numerical analysis and detection of cancer cells using a dual-core gold coated plasmonic biosensor

In this research, a simple dual-core photonic crystal fiber (PCF) that leverages surface plasmon resonance (SPR) to operate as a bio-sensor in the visible to near-infrared range is proposed. An external analyte channel is constructed by putting a gold plasmonic metal layer over the fiber sensor. A numerical investigation employing the wavelength interrogation approach reveals that the maximal wavelength and amplitude sensitivity are 22000 nm/RIU and 1561.4 RIU-1, respectively. The high wavelength resolution for this suggested sensor is 4.54 × 10−6 RIU, and that suggests a high detection range. The proposed sensor is designed for the detection of any molecules from the RI range 1.33 to 1.42, and it can detect six different types of cancerous cells (the refractive index of different cancerous cells varied from 1.380 to 1.401) in this range. According to the obtained numerical results, MCF-7 cells exhibit the highest wavelength sensitivity of 6428.6 nm/RIU and amplitude sensitivity of 766.361 RIU-1. Furthermore, the sensor will be able to detect different viruses, proteins, DNA/RNA strands, and other things in this sensing range. This sensor offered the potential to detect biochemical solutions and biological samples due to its high sensitivity and simple shape.

Aluminum-Based Plasmonic Photodetector for Sensing Applications

Plasmonic sensors have great potential for widespread usage. However, the prohibitive cost of noble metals restrains the wider adoption of these devices. The aim of our study is to develop a cost-effective Al-based alternative to common noble metal-based plasmonic detectors. We considered a structure consisting of an n-type doped Si wafer with a shallow p-n junction and an overlying Al grating with a trapezoidal groove profile. The RCWA (rigorous coupled-wave analysis) method was used to numerically calculate the distribution of absorbed light energy in the plasmonic detector layers and to optimize the grating parameters. Based on the simulation results, experimental samples of plasmonic photodetectors with optimal grating parameters (period—633 nm, relief depth—50 nm, groove filling factor—0.36, and thickness of the intermediate Al layer—14 nm) were manufactured, and their properties were studied. For these samples, we obtained a polarization sensitivity value of Ip/Is = 8, an FWHM of the resonance in the photocurrent spectrum ranging from 50 to 100 nm, a sensitivity at the resonance maximum of Iph = 0.04–0.06 A/W, and an angular half-width of photocurrent resonance of Δθ = 5°, which are comparable to noble metal-based analogs. Our results may be used for creating cost-effective high-sensitivity plasmonic sensors.

Saturated optical absorption in a mesoporous film decorated with a plasmonic layer

Porous materials with a large surface to volume ratio have found broad applications in fields from energy to environment. Here, we examine the linear and nonlinear optical response of a mesoporous film with vertical pores decorated with a layer of plasmonic nanostructures. Our measurements show that the plasmonic resonance leads to strong linear absorption from visible to infrared regions, which dramatically boosts the saturable absorptive nonlinear optical response with a modulation depth approaching 30 %. The strong absorptive nonlinearity enables immediate application as an optical switch for pulse generation in a fiber laser.

Formation of partially embedded Au nanostructures: Ion beam irradiation on thin film.

The Au partially embedded nanostructure (PEN) is synthesized by ion irradiation on an Au thin film deposited on a glass substrate using a 50 keV Ar ion. Scanning electron microscopy results show ion beam-induced restructuring from irregularly shaped nanostructures (NSs) to spherical Au NSs, and further ion irradiation leads to the formation of well-separated spherical nanoparticles. Higuchi's algorithm of surface analysis is utilized to find the evolution of surface morphology with ion irradiation in terms of the Hurst exponent and fractal dimension. The Au PEN is evidenced by Rutherford backscattering spectrometry and optical studies. Also, the depth of the mechanism behind synthesized PEN is explained on the basis of theoretical simulations, namely, a unified thermal spike and a Monte Carlo simulation consisting of dynamic compositional changes (TRIDYN). Another set of plasmonic NSs was formed on the surface by thermal annealing of the Au film on the substrate. Glucose sensing has been studied on the two types of plasmonic layers: nanoparticles on the surface and PEN. The results reveal the sensing responses of both types of plasmonic layers. However, PEN retains its plasmonic behavior as the NSs are still present after washing with water, which demonstrates the potential for reusability. RESEARCH HIGHLIGHTS: Synthesis of PENs by ion irradiation Utilization of Higuchi's algorithm to explore the surface morphology. Unified thermal spike and TRIDYN simulations being used to explain the results. Glucose is only used as a test case for reusability of substrate.

Double Polarization Peak Shift Sensitivity (DPPSS): An interrogation technique for a PCF SPR sensor

This research article provides a comprehensive analysis of a localized surface plasmon resonance (LSPR) based sensor, which operates in the visible to near-infrared region and uses a distinctive combination of two metals, ITO and Au as the plasmonic layers to achieve exceptional sensitivity. The wavelength spectrum that this sensor can now measure has been extended by combining these two materials in the RI region of 1.30 to 1.41, allowing the sensor to function in diverse fields such as bioimaging, biosensing, photocatalysis etc. A distinct and novel characteristic of the sensor which is termed as double polarization peak shift sensitivity (DPPSS) is proposed in this manuscript indicating the detection of resonance peak shift in both x-pol and y-pol simultaneously. DPPSS serves as the evaluative parameter for assessing the performance of the sensor. After optimizing all the structural parameters of the proposed sensor on the basis of DPPSS, it is found that the ultimate DPPSS value is 19560 nm/RIU and the maximum wavelength sensitivity is 19630 nm/RIU. Along with having a great sensitivity, the suggested sensor is fabrication friendly. The proposed research serves as a foundation for a thorough exploration of the LSPR phenomena for PCF in double metal scenario.

Optimized film thicknesses for maximum refractive index sensitivity and figure of merit of a bimetallic film surface plasmon resonance sensor

In this paper, a simple surface plasmon resonance (SPR) optical sensor with a bimetallic gold-silver film is proposed and its parameters are optimized based on reflectance spectra analysis. In comparison with most SPR sensors, which use single gold films, the evanescent field of this bimetallic configuration at the analyte–metal interface enables the sensing with substantially enhanced refractive index (RI) sensitivity and figure of merit (FOM). The proposed structure comprising a BK7 glass substrate, an adhesion layer of chromium, a gold-silver plasmonic layer, and a protective layer of silicon dioxide is employed in the Kretschmann configuration for liquid analyte sensing. In order to achieve the best sensing properties, the gold-silver layer thickness ratio is varied, and a thorough analysis of reflectance spectra is performed based on RI sensitivity and FOM. For this purpose, a liquid analyte of aqueous solutions of NaCl is employed for angles of incidence 63∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ $$\\end{document} and 64∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ $$\\end{document}, respectively. Moreover, based on the analysis, an optimized gold-silver layer thickness ratio is selected, and a sensitivity of 41,592 nm per RI unit (RIU) and FOM of 424 RIU-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document} are reached. The designed bimetallic SPR structure proves to be advantageous compared to single-gold-film structures employed for sensing applications.

Suppression of the plasmon-quenching effect on light amplification in 20-μm-diameter plasmonic whispering gallery mode resonators fabricated from bowl-shaped organic/metal thin films.

Bowl-shaped plasmonic whispering gallery mode (WGM) resonators were fabricated from a 10-nm-thick metal (Al, Ag, or Au) plasmonic layer that was covered with a 100-nm-thick 4,4'-bis(N-carbazolyl)-1,1'-biphenyl spacer layer and a 250-nm-thick 2,7-bis[9,9-di(4-methylphenyl)-fluoren-2-yl]-9,9-di(4-methylphenyl)fluorene light-emitting layer; the layer structure was grown on a 20-μm-diameter silica microsphere. When compared with a reference structure without the plasmonic layer, the resonators, which included either Al or Ag, showed almost the same threshold excitation intensities for generation of amplified spontaneous emission (ASE). This result indicates that the ease of light amplification in the plasmonic resonators was comparable to that in the reference structure. Excitons that exist in the vicinity of metal thin films are generally easy to quench because propagating surface plasmon polaritons (SPPs) absorb the exciton energy. Therefore, the observed comparability demonstrates that the plasmonic WGM resonators overcome this quenching effect on ASE via localization of the SPPs in the vicinity of the excitons.

Design of pseudo brain nano gold layer photonic crystal fiber sensor and investigation of fabrication accuracy

In this research, a new photonic crystal fiber sensor is proposed based on human brain scan images. As the human brain analyzes information in the cerebellum to make decisions, the use of this design and placement of air holes in the shape of human brain is the main reason of more electromagnetic field limitation in the center of the fiber or pseudo-cerebellum. Finite element method based on mode solver (FEM) is used to analyze this sensor. The size of the air holes and the thickness of the plasmonic layer are proposed in this design based on the Nelder-Mead optimization algorithm. The possible errors caused by the sensor fabrication are investigated and a unique equation is presented to estimate the effect of the size of the air holes on the sensor confinement loss. Numerical inference show that this brain shape sensor has an amazing maximum amplitude sensitivity (AS) of 7208 RIU−1 and appropriate maximum wavelength sensitivity (WS) of 10000 nm/RIU. Therefore, the proposed sensor has great prospects for medical, chemical and pharmaceutical measurements and diagnostic applications because of its high sensitivity, powerful detection and easy fabrication.

Nonlocal response of planar plasmonic layers

Nonlocal response of planar plasmonic layers

Plasmonic Modification of Epitaxial Nanostructures for the Development of a Highly Efficient SERS Platform

Epitaxy is the process of crystallization of monocrystalline layers and nanostructures on a crystalline substrate. It allows for the crystallization of various semiconductor layers on a finite quantity of semiconductor substrates, like GaAs, InP, GaP, InGaP, GaP, and many others. The growth of epitaxial heterostructures is very complicated and requires special conditions and the precise control of the growth temperature, the pressure in the reactor, and the flow of the precursors. It is used to grow epitaxial structures in lasers, diodes, detectors, photovoltaic structures, and so on. Semiconductors themselves are not suitable materials for application in surface-enhanced Raman spectroscopy (SERS) due to poor plasmonic properties in the UV/VIS range caused by missing free electrons in the conduction band due to the existing band gap. A plasmonic material is added on top of the nanostructured pattern, allowing for the formation of mixed photon–plasmon modes called localized surface plasmon-polaritons which stand behind the SERS effect. Typically, gold and silver are used as functional plasmonic layers. Such materials could be deposited via chemical or physical process. Attention has also been devoted to other plasmonic materials, like ones based on the nitrides of metals. The SERS performance of a functional surface depends both on the response of the plasmonic material and the morphology of the underlying semiconductor epitaxial layer. In the context of SERS, epitaxial growth allows for the fabrication of substrates with well-defined 3D nanostructures and enhanced electromagnetic properties. In this work, we described the possible potential plasmonic modification, composed of various coatings such as noble metals, TiN, and others, of well-developed epitaxial nanostructures for the construction of a new type of highly active SERS platforms. This abstract also highlights the role of epitaxial growth in advancing SERS, focusing on its principles, methods, and impact. Furthermore, this work outlines the potential of epitaxial growth to push the boundaries of SERS. The ability to design substrates with tailored plasmonic properties opens avenues for ultralow concentration detection.

Numerical Analysis of Solid-Core Photonic Crystal Fiber Based on Plasmonic Materials for Analyte Refractive Index Sensing

In this study, we presented a simple highly sensitive sensor based on commercially available solid-core photonic crystal fiber (PCF) and surface plasmon resonance (SPR) for measuring the refractive index (RI) of analytes. The numerical simulation based on the finite element method (FEM) has been examined to compute the optical properties such as confinement loss, power spectrum, and transmission intensity of the sensor. The most sensitive and inert plasmonic materials (gold and silver) have been assumed to be coated inside the fiber with the range of analyte RI from 1.32 to 1.40. The performance of the proposed sensor has been evaluated by tracing the several optical features like wavelength sensitivity, amplitude sensitivity, resolution of the sensor, and figure of merit. As a result, the comparative study between silver and gold elements has been carried out in which the maximum sensitivity received was 1.15 μm/RIU and 1.10 μm/RIU, respectively. Whereas, on the base of power spectrum, the obtained sensitivity was 513 μm/RIU for the gold layer. Moreover, the effect of other structural parameters (air holes and plasmonic layer thickness) on the sensing performance has been taken into an account. According to the simulation analysis and results, this sensor would have a great potential in various sensing applications of biomedical and liquid refractive index.

A two-fold SPR-SERS sensor utilizing gold nanoparticles and graphene thin membrane as a spacer in a 3D composite structure

Localized surface plasmonic resonance (LSPR) biosensing using optical fibers has gained popularity due to its label-free approach and high sensitivity to changes in the nanoparticle surface's local index of refraction. However, improving sensitivity remains a challenge. In this study, a two-step approach was employed to fabricate a composite structure using gold nanoparticles and monolayer graphene (Gr-AuNPs). The combination of AuNPs and graphene membrane demonstrated high potential for Surface-enhanced Raman scattering (SERS) and surface plasmonic resonance (SPR) fiber sensors. The Gr-AuNPs sensor successfully detected R6G molecules with a low detection limit of 10−12 M, indicating promising SERS activity. Numerical simulations confirmed that the graphene generated densely hot spots in the nanogap region between plasmonic layers. It's interesting that the proposed SPR-SERS Sensor can detect both glucose and thiram. This demonstrates the sensors practicality and can help with a basic environmental need to find leftover pesticides in the soil. The combination of SPR-SERS dual-mode detection provides more options for detecting and verifying data, increasing the precision and repeatability of experiments.