Plasmonics最新文献

This study explores the propagation characteristics of plasmon mode at non-uniform plasma-indium antimonide (InSb) interface in THz frequency regime. The primary goal of this work is to examine the combined effects of cyclotron frequency, plasma frequency, and InSb temperature on the dispersion relations of plasmon mode. We derive dispersion relation to analyze the effective mode index, propagation length, normalized phase velocity, cutoff frequency, and normalized propagation constant across THz frequency spectrum. Our results demonstrate that cyclotron frequency and plasma frequency of plasma medium profoundly influences the characteristics curves. Furthermore, temperature plays a critical role in modulating these plasmonic properties. The temperature effect provides additional degree of tunability for controlling the behavior of the plasmons, providing additional versatility for applications requiring precise thermal management and optimization. The combination of plasma parameters and temperature-dependent plasmonic behavior opens new avenues to design the nano-plasmonic devices with enhanced functionalities due to anisotropy of plasma medium.

Synthetic dyes, including indigo carmine (IC), are significant pollutants primarily because of their toxicity and resistance to conventional degradation methods. This study investigates the potential of ZnO nanoparticles as a photocatalyst for the degradation of indigo carmine under UV light. ZnO nanoparticles were synthesized using a simple water-based precipitation method and characterized via SEM, XRD, and UV–Vis spectroscopy. The photocatalytic degradation was optimized by adjusting experimental parameters such as the amount of catalyst, dye concentration, pH, and light intensity. The reduction rates for decolorization and chemical oxygen demand (COD) at the optimized operational conditions (pH 11, 32.3 W/m² light intensity, and 0.75 g/L ZnO) are 92% and 74%, respectively. The photodegradation followed pseudo-first-order kinetics, and the reusable ZnO catalyst experienced reduced efficiency. These findings suggest that ZnO nanoparticles may offer a low-cost and environmentally friendly alternative for wastewater treatment, with potential enhancements in catalyst reusability.

Metamaterial structures are versatile systems with unique characteristics, enabling various practical applications. Metamaterial absorbers (MAs) have recently gained significant attention for their remarkable absorption capabilities and tunable features. Terahertz (THz) MAs with sub-wavelength unit cells can manipulate THz radiation by either absorbing or transmitting it through carefully engineered structures. This study examines how unit cell design and structural parameters, including layer thickness, radius, and rod length, influence absorption spectra such as number of absorption peaks and bandwidth of multi-layer MAs in the THz range. The proposed multi-layer structure of MAs is composed of five layers arranged sequentially from bottom to top: a gold metal layer, a polydimethylsiloxane (PDMS) dielectric layer, a vanadium dioxide (VO₂) layer, a second PDMS dielectric layer and a top layer combining VO₂ with graphene. The findings show that adjusting the structural parameters can enhance the number of absorption peaks, reduce the bandwidth, and shift the spectrum. The proposed THz MAs have potential applications in diverse fields, including biosensors, photodetectors, and photonic switches.

Surface enhanced Raman scattering (SERS) is a highly sensitive and precise technique that enables the acquisition of high-quality spectra from materials in tiny quantities, down to the single-molecule level. Today, this technique, with its high signal enhancement factor, is considered an efficient tool for molecular detection in biosensors. This article will present and investigate the impact of uses of a novel hybrid silver-aluminum structure, a sensor, and also study the enhancement of SERS signal due to the plasmonic coupling effects. The results indicate that the hybrid multi-shape structure enhances the signal and enables a noticeable frequency shift in the Raman spectrum. Furthermore, the role of localized surface plasmon resonance (LSPR) and surface plasmon resonance (SPR) coupling in improving SERS performance is being investigated. It is found that the presence of multi-shape nanoparticles and the proposed arrangements optimize the plasmonic coupling between the localized surface plasmon and the surface plasmons of silver (Ag) and aluminum (Al), leading to an increased concentration of the electromagnetic field in the hotspot regions. We also present the results, the influence of various parameters on the spectral characteristics, and signal enhancement of SERS in the hybrid multi-shape structure. In this regard, the effect of the change in the inner radius of the nanostar from 10 to 100 nm and the use of different sequential arrangements of plasmonic materials, including gold (Au), silver (Ag), copper (Cu), aluminum (Al), and platinum (Pt), on electromagnetic field enhancement and SERS signal are being investigated. We show that in all configurations, the maximum SERS signal intensity occurs at an inner radius of 17.2 nm, reaching a value of 3.884 × 10⁷ /m. Additionally, the results for different sequential plasmonic material arrangements indicate that the Ag _ Al _ Ag configuration achieves the highest SERS signal intensity, with a value of 3.67328 × 10⁸ V/m. The Ag_Al_Ag structure achieves a sensitivity of 20.4 nm/RIU and a quality factor of 23.93. The corresponding enhancement factor (EF) for this structure has been calculated to be approximately 1.1 × 10⁷, indicating a significant enhancement in plasmonic sensor performance compared to previous designs.

Silver nanoparticles were synthesized on glass substrates via pulsed laser deposition at fluences of 2.5 and 8.3 J/cm². The number of laser pulses (300, 600, 900, and 1200) was varied to evaluate its impact on the surface plasmon resonance (SPR) absorption properties of the films. A Langmuir probe was used to characterize the plasma plume, allowing correlation between ion energy/density and nanoparticle features. The results show that both fluence and the number of pulses significantly influence the nanoparticle size, leading to changes in the position and width of the SPR absorption band. Atomic force microscopy revealed spherical nanoparticles with size variations depending on the laser fluence. The potential of these thin films as surface-enhanced Raman spectroscopy (SERS) substrates was investigated using methylene blue as a probe molecule. SERS spectra were collected from the film with the highest SPR intensity in the UV–Vis range, comparing spectra from different regions of the sample.

Surface plasmon resonance (SPR) sensors are essential for detecting several applications because of their high sensitivity and real-time analysis capabilities. This paper’s proposed sensor incorporates the CsF prism, gold (Au), silicon nitride (Si₃N₄), and zirconium nitride layers to detect the various applications. Au, which has excellent plasmonic qualities, greatly increases sensitivity. Additionally, incorporating Si₃N and ZrN, which have remarkable optical and electronic properties, improves signal enhancement by increasing light-matter interaction. The proposed sensor analyzes performance using the transfer matrix method (TMM) and Kretschmann configuration, which is based on Fresnel’s equation. At RI of 1.33–1.35 sensing analyte has the following maximum sensitivities (S) and figure of merits (FoM): 281.58, 294.44°/RIU and 38.85/RIU, 45.93/RIU with/without ZrN layer at remarkable minimum reflectance, respectively. According to the study, combining Si₃N₄ and ZrN materials with conventional plasmonic metals can improve sensitivity while serving as a platform for additional medical diagnostics and environmental monitoring.

This pragmatic study aims to synthesize nanoparticles from three noble metal elements as a core@shell of gold, silver, and palladium, and to study their optical, structural, and morphological properties, as well as to study the effect of these nanoparticles as antibacterial agents. A 532 nm Nd: YAG laser was used, and various durations of 10, 15, 20, and 25 min, at a repetition rate of 4 Hz and 1500 mJ energy, ablated the targets immersed in 10 ml of deionized water. The results of ultraviolet–visible spectroscopy showed that the colloidal nanoparticles of gold, silver, and palladium have surface plasmon resonances at 486, 510, 511, and 516 nm. The X-ray diffraction analysis exhibited the significant climax peaks at 2θ values of 38.6°, 44.7°, 64.8°, and 78.4°, and indicates that the nanoparticles have a cubic crystal structure that complies with the JCPDS. On the other hand, the analysis of the energy dispersive X-ray and the existence of pure nanoparticles was an affirmation. Furthermore, the field emission scanning electron microscope images showed crystalline core–shell nanoparticles, and the particle size was between 27 and 31 nm, agreeing with the results of the transmission electron microscopy, which explained that the nanoparticles have a double core of gold and silver and a shell of palladium. It was found that the prepared nanoparticles exhibit antibacterial activity against Staphylococcus aureus and Escherichia coli bacteria better than when compared to their activity when prepared as bimetallic or monometallic, potentially enabling their use in biomedical applications. According to the literature, this is the first time that the preparation of three nanoparticles of noble metals of gold, silver, and palladium as core–shell in deionized water using the pulsed laser ablation method has been reported.

Graphical Abstract

We present a self-referenced plasmonic sensor with a high surface sensitivity based on Au nanoislands synthesized by thermal dewetting on a planar SiO₂/metal bilayer deposited on a Si chip. The optical device displays two spectral features in reflection: a Fabry-Pérot resonance due to the SiO₂/metal bilayer and a localized surface plasmon resonance (LSPR) associated with the Au nanoislands, serving as a reference and sensing signal, respectively. Surface sensitivity was investigated through the study of bovine serum albumin protein adsorption. The device exhibited a surface sensitivity of 0.2 nm/(ng/cm²), an order of magnitude greater than other plasmonic devices based on Au nanoislands. The device response was theoretically modeled using rigorous coupled-wave analysis (RCWA) simulations, which showed strong agreement with the experimental results and provided design guidelines for further sensitivity improvement. The combination of high surface sensitivity, chip-based architecture, cost-effectiveness, and a straightforward Au nanostructure synthesis procedure positions this device as a promising self-referenced plasmonic sensor for biosensing applications.

Proteins play a crucial role in tissue formation and repair, making their accurate detection essential for biomedical applications. This study presents a square-core photonic crystal fiber sensor (SCPCFS) designed for the sensitive detection of protein concentrations in aqueous solutions. Zeonex is selected as the background material due to its superior optical characteristics in the terahertz (THz) frequency range. Operating within the 0.8–2.2 THz band, the sensor achieves high relative sensitivity at 1.6 THz, with values of 97.667%, 98.33%, 98.781%, 99.072%, and 99.242% corresponding to protein concentrations of 15%, 30%, 45%, 60%, and 75%, respectively. The associated confinement loss values are notably low—4.56, 9.89, 2.26, 5.87, and 2.25 cm⁻¹—indicating minimal signal attenuation. Furthermore, the SCPCFS demonstrates excellent performance across other key optical metrics. Its simple geometric structure facilitates fabrication using current technologies. These features highlight the sensor’s potential for reliable, real-time, and highly sensitive protein concentration monitoring in biomedical and biochemical applications.

A novel photonic crystal fiber structure with two elliptical air-holes at center, surrounded by two hexagonal rings of circular holes, has been investigated for its performance as a wide range SPR-PCF refractive index sensor. The analyte is applied to the outer plasmonic layer, made of gold. The proposed Plasmonic sensor supports the ease of fabrication due to its simplistic structure. The full vector finite element method has been utilized to examine the proposed Plasmonic structure, in terms of several performance metrics, such as confinement loss and sensitivities. The refractive indices between 1.36 and 1.41 have been taken into consideration for the analysis. The sensor has been designed to operate in the mid-infrared band, i.e., 2500–3800 nm. The proposed surface Plasmon resonance based PCF sensor has achieved a very remarkable sensor resolution of (1.67 times {10}^{-6}), as well as 148 per RIU of amplitude sensitivity, and an extremely impressive spectral/wavelength sensitivity of 60,000 nm/RIU. The analysis of the proposed design can be suitably extended to sense the other analytes, such as wide range of biomolecules, human body fluids, and other chemicals.