Plasmonics最新文献

We investigate surface plasmon polaritons (SPPs) modes in palladium (Pd)-coated silver double nanowires by using the finite difference time domain (FDTD) method. Since Pd can absorb hydrogen (H(_2)) and converts to Pd-H, its permittivity is completely different from that of Pd-H, so the optical response of the system will be also change. The results of electric field distributions and propagation lengths of seven modes of the designed structure are obtained by calculations. For different modes, it is found that the propagation length increases with the increase of mode order. The propagation lengths of the same mode in the structure of Pd and Pd-H are respectively compared, and it is discovered that it is also different due to the change of dielectric constant before and after H(_2) absorption. The results show that in the double nanowire structure, the propagation lengths of structures with Pd are larger than the ones of structures with Pd-H for each mode. The distance of the two nanowires impacts on the coupling between the two nanowires. By changing the radius of Ag nanowire, the propagation lengths of the fundamental mode increase, while the ones of the harmonic modes decrease. There is an optimal thickness to make the propagation length longest for each mode by changing the thickness of Pd, which shows the competition between the dissipation of the structure and the coupling between SPPs in different layers. The structure we designed can be applied to the direction of the hydrogen sensor to realize the monitoring of its state when using hydrogen energy to ensure safety.

We designed a single-layer patterned graphene metasurface composed of four L-shaped graphene strips, four rectangular graphene strips, and meter-shaped graphene block. Metasurface creates dual plasmon-induced transparency (PIT) through the interaction between light and dark modes. The transmission characteristics of the structure are analyzed using the coupled mode theory and the finite element method, and the structure realizes the function of the dual-frequency optical switch. At frequencies of 3.72 THz and 6.24 THz, the optical switch modulation amplitudes are 98.04% and 95.37%, respectively, and the corresponding insertion losses are 0.16 dB and 0.08 dB respectively. In addition, the proposed structure is insensitive to changes in the polarization angle of the incident light. Under the incidence of x-polarized light and y-polarized light, the PIT effect of the two structures is consistent. This research will present a new idea for the design of terahertz multi-frequency optical switches. The optical switch has great potential for various applications such as terahertz imaging, sensors, photodetectors, and modulators.

In this paper, a tunable low-pass optical filter based on metal–insulator-metal (MIM) structure with surface plasmon polaritons (SPPs) is proposed and discussed, which is composed of a bus waveguide containing two silver rods with square section (SRSS) and two semi-elliptical resonators (SERs) partially filled with Kerr material. After optimizing the structural parameters, a relatively ideal low-pass filtering effect is achieved. The minimum transmittance of the passband is 0.76, and the roll off coefficient (ROC) of the filtering barrier is up to 1.55 × 10⁻⁷ GHz⁻¹. Furthermore, based on the influence of refractive index on optical modes in the two SERs, the cutoff frequency of the filtering effect can be conveniently adjusted by controlling the external light field irradiated on the Kerr material. The sensitivity of the right cutoff frequency adjustment is 11.6 GHz·μm²/mW, accompanied by an increase in the ROC. The low-pass filter with tunable cutoff frequency may have promising applications in integrated optical communication and information processing.

The expeditious growth and development of different optical-based medical and biomedical instruments to detect various diseases nowadays put itself a potential research topic. In recent times, prevalence of diabetes mellitus among people has become alarming and often life-threatening. In this regard, efficient sensors with high sensitivity are extremely necessary for monitoring and quantification of glucose level in the urine samples. A self-referenced surface plasmon polariton sensor using trapezoidal TiO₂ grating on thin Au film has been proposed here to detect glucose level in urine samples for the first time. The proposed sensor has been optimized for better sensitivity and can be operated in the optical communication band which can help to achieve existing mature light sources and light detection instruments. The sensor has been designed with a thin dielectric grating on top of thin metal film resulting in generation of two surface plasmons at the two boundaries of the metal film. This technique is fascinating to improve the accuracy of sensitivity of the device and helps to eliminate cross-sensitivity problem. As a result, this type of self-referenced biosensor can be used for a wide range of applications in fields such as biochemistry, biophysics, and environmental monitoring. The proposed sensor shows a higher sensitivity compared to that of other plasmonic sensors reported in recent times due to incorporation of trapezoidal-shaped grating structure for the first time instead of rectangular shape. The spectral sensitivity of the proposed structure was obtained as 666.67 nm/RIU with optimized values of different structural parameters.

This research study specifically examines the CuO@ZnO nanoparticle core–shell colloidal solution that is produced using Nd: YAG laser ablation. The laser used has pulse energies of 900, 700, and 500 mJ, a wavelength of 1064 nm, and repeated pulses of 200. This work demonstrated the characteristics of a colloidal solution containing CuO@ZnO NP core–shell deposited onto Si substrates using the drop-casting process. The TEM, SEM, XRD, and UV–vis spectroscopy techniques were used to investigate the morphological, shape, optical, and structural characteristics of the synthesized CuO@ZnO NP core–shell. The XRD analysis reveals that the CuO@ZnO NP core–shell has sizes ranging from 30 to 93 nm approximately. The nanoparticle core–shell exhibited a combination of spherical and irregular shapes with sizes ranging from 30 to 90 nm. The nanoparticle size appeared to be influenced by the variation in laser pulse energy, as evidenced in SEM pictures. The TEM pictures reveal that the core–shell nanoparticles exhibit a particle size distribution with average sizes of 19, 70, and 30 nm for the nanoparticles produced using laser pulses with energy levels of 900, 700, and 500 mJ, respectively. The TEM pictures also exhibit a dark central region of CuO NPs and a comparatively lighter outside region of the ZnO nanoshell, thereby verifying its core–shell structure. Alteration of the laser energy resulted in a noticeable change in the optical energy band gap in the generated samples. The results of the UV–vis test suggested that a change in the energy of the laser pulse caused a change in the energy gap that ranges from 2.6 to 3 eV. The dye degradation capability of CuO@ZnO NP core–shell has been evaluated using methylene blue (MB), an organic dye. The results indicate that all samples exhibited successful degradation using CuO@ZnO NP core–shell with differentiated activity levels. The blue color of the methylene blue solution vanished within 120 min of exposure to illumination when the CuO@ZnO nanoparticles, generated with a laser energy of 900 mJ, were present. The investigation of CuO@ZnO nanoparticles, synthesized through the use of laser pulse energy, demonstrates its potential as a highly effective substance for water purification.

Malaria continues to be a major global health issue, impacting millions each year and leading to hundreds of thousands of deaths, especially in less developed areas. Timely and precise diagnosis is essential for effective treatment and management of this parasitic illness. This study presents the design and evaluation of a tunable terahertz (THz) metasurface biosensor tailored for malaria detection, integrating plasmonic materials with artificial intelligence. The biosensor employs a multi-layer structure comprising graphene, gold, and silver to leverage surface plasmon resonance effects. Comprehensive electromagnetic simulations and parameter optimization demonstrate the sensor's ability to detect minute changes in malaria parasite concentrations, achieving a peak sensitivity of 429 GHzRIU⁻¹, detection accuracy of 25.6 and a figure of merit of 10.989 RIU_-1. The sensor features tunable elements that allow dynamic performance adjustments. Additionally, the XGBoost machine learning algorithm is harnessed to predict sensor performance across various design parameters, consistently demonstrating maximum R² ranging up to 100%. This fusion of advanced materials, precise engineering, and predictive analytics represents a significant advancement in biosensing technology for malaria detection, offering substantial potential for early and accurate diagnosis.

An optimized prism-based surface plasmon resonance (SPR) sensor, containing a specific material combination, is represented for the accurate detection of the human blood group at a wavelength of 633 nm. The sensor structure includes a BK7 prism as a substrate followed by sequential deposition of silver (Ag), bismuth ferrite (BiFeO(_{textbf{3}})), black phosphorus (BP), and zinc telluride (ZnTe). The angular interrogation method (ATM) is used to investigate the performance parameters of the sensor, which include sensitivity, detection accuracy, and quality factor. Design and performance analysis is conducted using COMSOL, a finite element method (FEM)-based multiphysics software. Optimization of the thickness of the layers is done to get the highest possible outcome. For resonance and non-resonance conditions, magnetic field propagation and electric field distribution are determined which specifies an enhanced electric field at the metallic layer. The enhanced electric field is produced due to the metallic layer which reflects and redirects the electric field and provides a significant advancement in the performance parameter. The numerical calculations of the sensor parameters are obtained with the sensing medium immobilized with different blood groups (A, B, O). The highest sensitivity, detection accuracy, and quality factor for the detection of blood group A are 298.17 (^{circ })/RIU, 2.2, and 130.1 RIU(^{mathbf {-1}}); for the detection of blood group O are 327.79 (^{circ })/RIU, 1.98, and 95.35 RIU(^{mathbf {-1}}); and for the detection of blood group B are 330.86 (^{circ })/RIU, 1.73, and 81.33 RIU(^{-1}), respectively. The numerical analysis of the sensor parameters assures a significant improvement in the performance compared to previous research studies.

The work function and tunable photoluminescence of gold nanoparticles (AuNPs) and their interaction with Rhodamine 6G (R6G) molecules were characterized using scanning probe microscopy (SPM) and spectroscopy techniques. Atomic Force Microscopy (AFM) and Kelvin Probe Force Microscopy (KPFM) were employed to analyze the surface roughness and work function of AuNPs ranging in size from 3 to 21 nm. According to measurements with Kelvin Probe Force Microscopy (KPFM), the work functions for AuNPs are approximately 5.17 eV, 5.14 eV, and 5.13 eV for the range of sizes of nanoparticles. It was observed that larger AuNPs have increased surface roughness and consequently decreased work function. Additionally, phase imaging and Electrostatic Force Microscopy (EFM) were utilized to further investigate the AuNPs/R6G composites, revealing their surface nanoscale distribution and their electrical properties. In addition, the tunable photoluminescence of AuNPs based on excitation wavelength was studied, showing that as the excitation wavelength increases, the photoluminescence shifts to higher emission wavelengths and the peak intensity increases. Furthermore, UV–visible absorption and photoluminescence spectroscopy were employed to investigate the optical properties of AuNPs added to Rhodamine 6G molecules, revealing an enhancement in absorption and a reduction in photoluminescence.

Fiber-optic surface plasmon resonance (FO-SPR) sensors look at the absorbance of reflected light to measure changes in refractive index (RI). FO-SPR sensor modeling is essential in understanding the underlying processes that induce such RI changes. Despite two types of rays, i.e., skew and meridional rays, an FO-SPR model has been developed in the literature that only considers meridional rays. This meridional model has proven its applicability in several publications using pass-through FO-SPR sensors. However, this simplified FO-SPR model fails to simulate back-reflecting FO-SPR sensors properly, where diffuse light is delivered and collected at the same optical fiber end. Here, it is shown that a generalized FO-SPR model that includes skew rays more accurately simulates the spectra obtained in back-reflecting FO-SPR sensors. With the changing incidence plane of a skew ray in mind, the generalized FO-SPR model was built with three-dimensional polarization ray-tracing calculus. The necessary angular ray distribution of the back-reflecting FO-SPR sensor was acquired by a Monte Carlo three-dimensional ray-tracing simulation. Next, the effect of including optical components and deviations and model optimization by adjusting the gold relative permittivity and thickness was evaluated. The generalized model simulated FO-SPR absorbances with smaller widths than the experimental FO-SPR absorbances. The cause of this difference in absorbance is unclear and demands more research. Nevertheless, the skew ray incorporation in the generalized FO-SPR model enabled its application to a greater diversity of FO-SPR sensors compared to the simplified FO-SPR model both as a predictive and an analytic tool in the development of FO-SPR sensors.

Aqueous solutions are fundamental to a wide range of chemical and biological processes, serving as a critical medium for both natural phenomena and technological advancements. This study presents the design and modelling of a metasurface-based biosensor for aqueous solution detection. The sensor architecture comprises multiple resonators deposited on a silicon dioxide substrate, with materials selected for their specific optical properties. Finite element analysis was employed to simulate the sensor’s signal transduction mechanisms. The optimized design exhibits a sensitivity of 500 GHzRIU⁻¹ and a figure of merit of 10.638 RIU⁻¹. Comprehensive characterization of the sensor’s performance includes evaluation of its detection limit, dynamic range, and signal-to-noise ratio, all of which demonstrate superior target detection accuracy. The sensor’s versatility is further illustrated through its application in encoding operations, leveraging on the transmittance values to perform logic functions. A polynomial regression model was developed to interpolate absorption values at intermediate frequencies, achieving an R² value of 1.0, indicating perfect correlation between predicted and simulated data. These results suggest significant potential for the sensor’s application in high-precision biomolecular detection across various fields, including biomedical diagnostics and environmental monitoring.