Plasmonics最新文献

The design of nanostructure colors is influenced by mechanisms such as quantum size effects, surface plasmon resonance, and structural coloration. These optical properties arise from the interaction between localized magnetic and electric dipole resonances, rendering them highly sensitive to changes in geometric parameters. However, conventional analytical methods are inefficient in optimizing geometric parameters to achieve target colors, particularly when faced with the challenges of large-scale and diverse structural color designs. To address this limitation, we propose a design framework based on a bidirectional deep neural network (DNN) consisting of both a forward network and an inverse design network. The forward network learns the relationship between geometry and color response through parameter scans, enabling precise color prediction for specific geometries. The inverse design network derives the corresponding geometry from target color coordinates (CIE1931 color space) and tackles the multi-solution challenges in inverse design by cross-validating with the forward network. Rigorous computational modeling demonstrates that this approach can generate over one million visible-spectrum nanostructure colors with a theoretically predicted color reproduction rate exceeding 98%. This research presents a highly efficient and accurate framework for the design of high-precision optical components, including those used in silicon-based color processing, optical displays, sensors, and photovoltaic systems.

A comprehensive investigation of both spectral characterizations and sensing performance of a Pd-Au core–shell dimer is conducted theoretically by the finite-difference time-domain (FDTD) numerical tool. The extinction spectrum of the two-particle model exhibits the excitation of three hybrid resonance modes, which introduces a reliable multi-site sensing platform for bio/chemical molecules. Altering either the core size (r_c) or the shell thickness (t) significantly impacts the overall optical properties, illustrating controlled optical tunability over a wide range of frequencies extending from the UV to the visible region. Increasing the shell thickness considerably improves sensing capability to changes in the dielectric properties of the host matrix. To maintain simultaneous and effective sensing standards at several spectral sites, a structural ratio of t ≤ (3/2)r_c should be maintained. Otherwise, the sensing performance of the high-energy site is degraded with any further increase in t. The optimal sensing performance is achieved for a core radius of r_c = 10 nm and a shell thickness of t = 15 nm, where both low- and high-energy plasmonic modes exhibit enhanced sensitivity factors. The structural tunability of the proposed bimetallic dimer provides detailed guidelines for designing plasmon-based nanosensors. Additionally, we conclude that our theoretical observations will have profound implications for the use of extinction cross-section spectra in characterizing bimetallic core–shell dimers.

Metasurfaces, as ultra-thin two-dimensional structures with subwavelength patterns, can achieve flexible control over beam phase, amplitude, and polarization. However, most existing metasurfaces can only control beams from a specific incident direction, limiting their potential applications. This paper proposes a non-interleaved, bidirectional multifunctional Janus metasurface, which can be used to control terahertz waves over the entire space. By integrating photosensitive silicon—a phase-change material whose properties can be modulated by light—the functionality of the Janus metasurface can be dynamically reconfigured through changes in illumination intensity. With two input parameters—electromagnetic wave propagation direction and the state of the photosensitive silicon—four independent beam control functionalities are realized. Based on the proposed four-channel metasurface, a beam focusing characterization half-adder is designed for simple optical computation. The Gerchberg-Saxton (GS) algorithm is then used to design four near-field imaging phase encoding distributions to validate the performance of the proposed four-channel metasurface. A series of simulation results indicate that the reconfigurable Janus metasurface effectively reduces crosstalk between channels, and the simulation results of each channel match the expected design. Our work is of great significance for advancing multifunctional, miniaturized metasurfaces, and the proposed metasurface devices have many potential applications in optical computation, imaging, and communication.

Ascorbic acid, commonly called vitamin C, is a major biomarker of many malfunctions and deficiencies in the human body. This research focuses on enhancing ascorbic acid detection sensitivity using a specialized (single-mode, multimode, and single-mode) SMS fiber structure through enzyme functionalization and leveraging localized surface plasmon resonance (LSPR). The SMS fiber structure, designed for versatility, was modified to increase selectivity by ascorbate oxidase functionalization, which oxidizes the AA in the presence of oxygen, while LSPR techniques were employed to harness plasmonic effects for improved detection capabilities using gold nanoparticles (AuNPs), whose absorbance peak wavelength appeared at 522.8 nm. The resulting sensor probe was examined for various concentrations of AA ranging from 50 to 120 µM in terms of different performance parameters such as sensitivity, limit of detection, selectivity, reproducibility, and repeatability for ascorbic acid detection and such studies could be employed in complex biological matrices for AA detection. The sensor demonstrated a sensitivity of 0.0138 nm/μM and a calibration correlation factor of 0.9181, good linearity over the range of 50–120 µM AA concentrations. Additionally, the resulting fiber structure displayed selective detection of AA, thus ensuring non-interference of other analytes present in the realistic biological matrix. This research holds promise for advanced applications in clinical diagnostics and biomedical research, offering a novel and effective approach to enhance ascorbic acid detection.

This study investigated the influence of the degree of polydispersity of silver nanoparticles on plasmon-enhanced photoluminescence (PL) and surface-enhanced Raman scattering (SERS), which is crucial for the development of sensitive sensors. Experimental and theoretical modeling demonstrate the advantages of silver nanoparticles (~ 30 nm) with higher polydispersity and polymorphicity over monodisperse particles in enhancing the photoluminescence of a "green" luminophore, as well as SERS and resonance SERS (SERRS) of dyes under green light excitation within the resonance range of individual silver nanoparticles. When red excitation (620 nm and 633 nm) within the plasmon resonance of silver nanoparticle aggregates was used, no significant effect of Ag nanoparticle polydispersity on the enhancement of PL, SERS, or SERRS was observed. These findings highlight the importance of considering metal nanoparticle polydispersity when optimizing sensor systems based on plasmonic enhancement and challenge the conventional prioritization of monodispersity in plasmonic sensor design and offer practical guidelines for optimizing enhancement efficiency.

In this article, we present a passive plasmonic metasurface sensor, the square annular cavity array (SACA), designed for ultrasensitive refractive index (RI) detection, structural color modulation, and multiwavelength spectral filtering. This sensor is built on a multilayer plasmonic architecture comprising silver (Ag), silicon nitride (Si(_3)N(_4)), and silicon dioxide (SiO(_2)), featuring tunable square annular nanocavities with gap sizes ranging from 10 to 110 nm. These cavities are engineered to support hybrid plasmon–Fabry–Pérot resonances over a wavelength range of 400 to 1800nm. Finite element method (FEM) simulations conducted in COMSOL and optimized using the Nelder–Mead algorithm reveal the highest sensitivity of 800 nm/RIU, a spectral figure of merit (FOM) of 85.23, a quality factor (Q-factor) of 167.61, and a dots per inch (DPI) value of 169,333. The SACA sensor displays distinct chromatic transitions influenced by changes in the refractive index and angle of incidence. These effects are quantitatively assessed using the CIE 1931 color space under standard D65 illumination, facilitating label-free visual detection. Angle-resolved analysis reveals polarization-dependent mode splitting of up to 30(^{circ }), facilitating multiplexed spectral filtering and sensing. The normalized sRGB color gamut coverage is calculated to be 85.90% under RI modulation, indicating a design balance between visual expressiveness and functional spectral performance. By integrating high RI sensitivity, tunable spectral response, and real-time colorimetric feedback within a compact passive structure, the SACA sensor offers significant advantages. This design provides a versatile solution for point-of-care diagnostics, lab-on-chip optics, and integrated photonic applications.

A novel duplex-channel biosensor designed for simultaneous detection of cervical cancer and adrenal gland cancer is proposed here. The surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) uses a thin film of Ta₂O₅ and gold for cancer cell detection. The finite element method (FEM)-based confinement loss (C_L) analysis is used for geometrical optimization. The right and left slots are denoted by Channel 1 (Ch1), and Channel 2 (Ch2) is the label for vertically positioned top and bottom slots, respectively. Two channels are separated by a thick barrier of silica layer to prevent direct contacts between two neighboring channels such that the analytes in each channel will not mix up. Simulation results show that Channel 1 with adrenal cancer cells supports y-polarized electric field modes, whereas Channel 2 with cervical cancer cells supports x-polarized modes. For cervical and adrenal cancer cells, the sensor’s amplitude sensitivities are 1168.83 RIU⁻¹ and 394.29 RIU⁻¹, respectively, while its wavelength sensitivities are 8333.33 nm/RIU and 12,142.86 nm/RIU. The suggested sensor is a circular-shaped, dual-channel PCF sensor capable of detecting two separate analytes at the same time. The sensor uses an external sensing technique, which is affordable; liquid sample infiltration will be simpler, and it will make the sensing mechanism more convenient. With the ability to identify multiple cancer cells at once, the suggested sensor is a good fit for the biosensing applications in healthcare.

Tin sulfide, particularly in its π-phase with a cubic crystal structure, has demonstrated significant potential for use in flexible photodetector applications due to its unique optoelectronic properties. However, its performance is often limited by low photocurrent and, consequently, low responsivity. This study addresses this challenge by introducing a novel approach to enhancing photodetector performance through copper doping. A thin film of copper-doped tin sulfide (SnS: Cu) was grown on a flexible polyester substrate using the cost-effective and straightforward chemical bath deposition (CBD) technique. The photoresponse measurements demonstrated an increase in responsivity of approximately 56 times compared to what was previously reported for undoped SnS thin films in our earlier study. Furthermore, the present photodetector exhibited a strong response across a wide range from UV to near-infrared illumination. X-ray diffraction (XRD) confirmed the preservation of the cubic SnS phase. Field emission scanning electron microscopy (FE-SEM) revealed a homogeneous, quasi-spherical grain structure. Energy-dispersive X-ray spectroscopy (EDX) confirmed the presence of Cu in the film, and the systematic shift of XRD peaks toward higher diffraction angles indicates that Cu is incorporated into the SnS lattice, consistent with substitutional doping. The optical measurements indicated a bandgap of 1.44 eV. The responsivity (R) and detectivity (D) were also calculated at 380 nm, 750 nm, and 850 nm. These findings underscore the potential of Cu-doped SnS thin films as next-generation flexible optoelectronic devices.

This study presents a theoretical framework for achieving subwavelength atomic localization using surface plasmon polaritons (SPPs) in a four-level atomic system. By exploiting the strong field confinement and enhanced near-field effects of SPPs, we demonstrate high-precision atom positioning through quantum interference phenomena. The proposed model utilizes a combination of probe and control fields to generate spatially dependent absorption profiles, enabling atom localization with nanometer-scale resolution. Numerical simulations reveal distinct localization patterns dependent on phase modulation and detuning parameters, with peak resolutions reaching (lambda /20). The interaction between SPPs and atomic states is shown to overcome traditional diffraction limits while maintaining robust coherence properties. These results suggest new possibilities for quantum control at the nanoscale, with direct applications in atom trapping, nanolithography, and plasmon-enhanced spectroscopy. The analysis further identifies optimal conditions for minimizing decoherence effects while maximizing spatial resolution in plasmonic nanostructures.

The study presents a theoretical and computational study of a ZBLAN fiber-based SPR sensor in the NIR region of wavelength. Malignant liver tissues are considered as analytes, and the analysis is carried out under the phenomenon of optimum radiation damping (ORD). The sensor architecture incorporates an amorphous silicon (a-Si) substrate and silver metal (Ag) along with tellurium dioxide (TeO₂) as an absorption enhancement layer. Utilizing the dynamic nature of ORD, the quantitative analysis is carried out to observe the contribution of individual layers, their respective thicknesses, and operating wavelength towards absorption enhancement and optimization of figure of merit (FOM). The results are further explained in terms of physical concepts such as power loss, field enhancement, and Rayleigh scattering in the sensors. The systematic optimization of thickness and wavelength led to a maximum FOM of 15,810 RIU⁻¹ with an extremely small FWHM (width of spectrum) of 0.012°. The calculated power loss ratio (PLR) is 6.039 with combined performance factor (CPF) of 92337 μm⁴/RIU. After optimization, the PLR enhances by nearly five times to the initial values. A high PLR and FOM values show ultrasensitive detection, while a small FWHM shows well detectable sensing of malignancy in liver tissues. To the best of our knowledge, the exploitation of ORD for the detection of liver malignancy using ZBLAN fiber, NaF cladding, and an a-Si/Ag/TeO₂ heterostructure has been explored for the first time.