Electric Field Intensity Enhancement Research Articles

Silicon nanoparticle-based near-infrared surface enhanced fluorescence without any “dielectric spacer”

For the first time, herein, we report the theoretical investigation on silicon (Si) nanoparticle-based near-infrared (NIR) surface-enhanced fluorescence (SEF). Initially, the scattering spectra of single spherical-shaped Si nanoparticles of different sizes are plotted and characterized all the observed modes using the multipolar decomposition method. Later, the electric field intensity enhancement (EFIE) distribution inside and outside Si nanoparticles is plotted at the wavelengths of electric and magnetic type modes. Finally, the SEF enhancement (χSEF) is estimated by varying the excitation wavelength (λex), fluorescence wavelength (λem), and separation (d) between the fluorophore and Si nanoparticle of different sizes. The χSEF is found to vary from 1 to 3 orders of magnitude when the λem falls in the NIR region. In contrast to the plasmonic or metal nanoparticle-based SEF, the maximum χSEF is observed when d = 0. This indicates that the thin dielectric spacers between the fluorophores and Si nanoparticles are not required to obtain the enhancement in the case of the Si nanoparticle-based SEF technique. This can be considered as a significant advantage over the conventional metal nanoparticle-based SEF, where dielectric spacers are mandatory. Finally, the average SEF enhancement ⟨χSEF⟩ is also estimated.

Field enhancement of epsilon-near-zero modes in realistic ultrathin absorbing films

Abstract Using electrodynamical description of the average power absorbed by a conducting film, we present an expression for the electric-field intensity enhancement (FIE) due to epsilon-near-zero (ENZ) polariton modes. We show that FIE reaches a limit in ultrathin ENZ films inverse of second power of ENZ losses. This is illustrated in an exemplary series of aluminum-doped zinc oxide nanolayers grown by atomic layer deposition. Only in a case of unrealistic lossless ENZ films, FIE follows the inverse second power of film thickness predicted by S. Campione, et al. [Phys. Rev. B, vol. 91, no. 12, art. 121408, 2015]. We also predict that FIE could reach values of 100,000 in ultrathin polar semiconductor films. This work is important for establishing the limits of plasmonic field enhancement and the development of near zero refractive index photonics, nonlinear optics, thermal, and quantum optics in the ENZ regime.

Synergistic effect of total ionizing dose on single-event gate rupture in SiC power MOSFETs

The synergistic effect of total ionizing dose (TID) and single event gate rupture (SEGR) in SiC power metal–oxide–semiconductor field effect transistors (MOSFETs) is investigated via simulation. The device is found to be more sensitive to SEGR with TID increasing, especially at higher temperature. The microscopic mechanism is revealed to be the increased trapped charges induced by TID and subsequent enhancement of electric field intensity inside the oxide layer.

High performance SPR biosensor using Cu-Pt bimetallic layers and 2D materials

In this present paper, we propose a surface plasmon resonance(SPR)sensor having better performance parameters based on Kretschmann configuration. The proposed SPR sensor is a modified Kretschmann configuration comprised of BK7 prism-Cu-Pt-Graphene/BP/WS2. The bimetallic layer provides consistent enhancement of sensitivity over other SPR structures. Extensive numerical analysis based on transfer matrix theory has been performed to characterize the sensor response considering sensitivity, full width at half maxima (FWHM), detection accuracy(DA), quality factor(QF) with other conventional reported SPR sensor. We have also analyzed the electric field intensity enhancement factor(EFIEF) for the proposed SPR sensor. We have found that maximum sensitivity of 309deg/RIU corresponds to the four layer of BP configuration. We believe that this proposed SPR sensor could find the new platform for the chemical examination, medical diagnosis, gas detection and biological detection.

Engineering Electromagnetic Field Distribution and Resonance Quality Factor Using Slotted Quasi-BIC Metasurfaces.

Dielectric metasurfaces governed by bound states in the continuum (BIC) are actively investigated for achieving high-quality factors and strong electromagnetic field enhancements. Traditional approaches reported for tuning the performance of quasi-BIC metasurfaces include tuning the resonator size, period, and structure symmetry. Here we propose and experimentally demonstrate an alternative approach through engineering slots within a zigzag array of elliptical silicon resonators. Through analytical theory, three-dimensional electromagnetic modeling, and infrared spectroscopy, we systematically investigate the spectral responses and field distributions of the slotted metasurface in the mid-IR. Our results show that by introducing slots, the electric field intensity enhancement near the apex and the quality factor of the quasi-BIC resonance are increased by a factor of 2.1 and 3.3, respectively, in comparison to the metasurface without slots. Furthermore, the slotted metasurface also provides extra regions of electromagnetic enhancement and confinement, which holds enormous potential in particle trapping, sensing, and emission enhancement.

Study of surface enhanced fluorescence of CdSeS/ZnS alloyed quantum dots using cytop layer as a dielectric spacer

Recently, the surface enhanced fluorescence technique has been helpful for several biological applications. Some researchers have reported the SEF of fluorophores such as dye molecules and QDs using dielectric spacers formed by several approaches. Herein, for the first time, we report the SEF spectra of CdSeS/ZnS alloyed quantum dots (QDs) that have high photostability, less toxicity, and high biocompatibility. Interestingly, the thin cytop layers formed by a simple approach are used as “dielectric spacers” between Au nanoparticles in the plasmon-active substrate (PAS) and the QDs. For comparison, the spectra of QDs dispersed directly on (i) bare PAS, (ii) bare glass substrate, and (iii) cytop coated glass substrate are also recorded. The enhancement factor is found to vary from one to two orders of magnitude. Since the SEF enhancement depends on the electric field intensity enhancement (EFIE) in the PASs, Finite Element Method (FEM) simulations are performed to estimate the EFIE and its dependence on the thickness of the cytop layer and size of the nanogap between nanoparticles in the PASs.

Modeling of High-Performance SPR Refractive Index Sensor Employing Novel 2D Materials for Detection of Malaria Pathogens.

The present work exhibits a novel design of surface plasmon resonance (SPR) biosensor, which comprises CaF2 prism, TiO2, metal (Ag/Au), PtSe2, 2D materials (graphene/transition metal dichalcogenides (MoS2/WS2)) and sensing medium, for point-of-care detection of various stages of malaria diseases. The transfer matrix method (TMM) is employed to examine the angular reflectivity of the proposed structure after judiciously optimizing the layer thicknesses and layer numbers. Phase interrogation technique is utilised to validate the position of occurrence of resonance angles. Additionally, the proposed SPR structure is designed using COMSOL Multiphysics, to assay the electric field intensity and electric field enhancement factor near the edge of 2D material-sensing layer interface. Simulation upshots revealed that the use of new class of 2D materials catapult the sensor performance to a new height compared to the traditional SPR configuration. A maximum sensitivity of 240.10°/RIU, quality factor of 78.46 RIU-1 and detection accuracy of 1.99 is attained for Ag-based SPR configuration with bilayer of WS2. Sensing parameters are compared with previously reported works to prove the superiority of the present research. Moreover, the real-time and label-free detection of malaria diseases makes the suggested sensor worth to fabricate as a SPR chip with the recent nanofabrication technologies.

The evolution of nano-precursors at film-substrate interface under nanosecond laser irradiation

Functionally graded layers (FGLs) with quasi-continuous interfaces are deposited by ion-beam sputtering (IBS). The laser-induced damage threshold (LIDT) of FGLs is more than twice that of film-substrate interface. Basic time-resolved microscope system is designed to capture the ultrafast dynamics process of nanosecond laser-induced damage in FGLs and film-substrate interface, respectively. Materials ejections and damages craters at the film-substrate interface are observed by focused ion beam (FIB) microscope. The primary sources leading to low LIDTs are the nano-precursors distributed among the subsurface. The nano-precursors formed by the metastable chemical structures (FeOx and CeSixOy) are agglomeratedand grown during migration process because of sputtered atomic collision motion. High normalized electric field intensity enhancement in the subsurface region (about 275 nm) is considered to be an important factor that promotes absorption of the nano-precursors. The experiment first provides a sufficient experimental observation of the laser-induced damage process inside films which deepens people’s understanding of nano-precusors and lays a solid basis for solving the damage of film-substrate interface.

Characteristic parameters of photonic nanojets of single dielectric microspheres illuminated by focused broadband radiation

Herein, we report the theoretical investigation on the photonic nanojets (PNJs) of single dielectric microspheres illuminated by focused broadband radiation (polychromatic light) from a Halogen lamp, supercontinuum source, light-emitting diode, and Hg arc lamp. The role of incident beam waist, refractive index of the surrounding medium, and radius of the microsphere on the characteristic parameters such as the electric field intensity enhancement, effective width, and length of the PNJ is studied. Interestingly, the characteristic parameters of the PNJs of solid microspheres obtained for the above-mentioned broadband radiation sources are found close to those observed for the focused monochromatic radiation of wavelengths which are near to the central wavelengths of the sources. Moreover, the characteristic parameters of PNJs of the core–shell microspheres of different thicknesses (t) illuminated by polychromatic radiation from most commonly used sources such as Halogen and Hg arc lamps are studied. For each t value, a suitable wavelength of monochromatic radiation has been found to generate the PNJ with characteristic parameters which are close to those obtained in the case of polychromatic radiation. We believe that the analytical theory and the theoretical simulations reported here would be useful for researchers who work in the fields such as PNJ assisted photoacoustic spectroscopy, white light nanoscopy, low-coherence phase-shifting interference microscopy, and Mirau interferometry.

Blood Hemoglobin Concentration Sensing by Optical Nano Biosensor-Based Plasmonic Metasurface: A Feasibility Study

Erratic in concentration of the blood hemoglobin (Hb) is pernicious and common disease in many humans worldwide. The establishment of Hb measurement led to finding bio-optics mechanisms for tunable and high sensitivity dual-band plasmonic metasurface (PM) configuration that studied for Hb concentration detection of blood and formed by a semiconductor integrated with metal and dielectric layers. However, finding particularly useful mechanisms without surgery is a safe method with several potentials in biomedical applications. In this paper, a biosensor based on surface plasmon resonances (SPRs) that is a label-free detection method is proposed to measure Hb concentration of blood. The presented sensing method is susceptible to being a dual-bands metasurface perfect absorber at room temperature to adjust the optical properties of the integrated semiconductor plasmonic structure. The modeling and numerical performance have been fulfilled based on the finite element method (FEM) using an electromagnetic field simulation software (CST). Also, to validate the numerical results, the transfer matrix method (TMM) was introduced as an analytical model. The analytical and numerical results show a good agreement. Results indicate maximum sensitivity, figure of merit (FoM), and quality factor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ) as 315 nm/RIU, 398.8, and 1407.6, respectively. By controlling and harnessing the light-matter interaction in near-infrared (NIR) region, we obtained the giant electric field intensity enhancement (EFIE) as 5000 and the maximum absorption close to 1 in the first resonance peak of λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> = 1.126 µm which is the best track of optical operation in NIR regime. By adding samples to the biosensor, different Hb concentrations of 0 g/L to 260 g/L have been detected from 1.11 µm to 1.17 µm. Furthermore, the proposed optical metasurface design can be utilized as a biosensor to measure the different content of Hb concentration in whole blood on a g/L scale, making it one of the best candidates for the future optical biosensors for biomedical applications.

The Effectiveness of Mitigation Schemes on Electric Field Intensity (Stress Control) for Overhead Line Glass Insulator

This paper presents the simulation results of electric field distribution within suspension insulators on different stress control techniques under dry-clean and polluted conditions. Finite element method (FEM) is adopted to estimate the electric field behaviour along the insulator profile. For this study, COMSOL Multiphysics version 5.3a is used to perform the modelling and executing the field analysis. The effectiveness of zinc-oxide (ZnO) micro-varistor and grading ring as mitigation tools for the electric field intensity enhancement was examined in this study. The reference data from the dry-clean condition was used as the benchmark to examine the effect of pollution on electric field distribution on the insulator surface. It was found that the application of the combined techniques of ZnO micro-varistor and grading ring is the best scheme for stress control as it reduced the electric field intensity up to almost 84% for both dry-clean and polluted conditions. This study also found that the positioning the grading and corona ring is crucial as it will affect the electric field intensity distribution

Aperture-type terahertz near-field imaging with a cylindrical frustum-shaped plastic probe.

We designed an aluminum-coated plastic probe made from the combination of cylinder and a frustum of a cone for terahertz near-field imaging. The bunching width of the probe is 12 µm and the electric field intensity enhancement factor just outside the probe tip reaches up to 25. An imaging resolution obtained through near-field imaging experiments on a variety of targets, including narrow metals and narrow media, is 6 µm (λ/450) at 0.11 THz. By adopting an adaptive threshold segmentation image processing algorithm that combines Hilbert scanning and wavelet transform, the influence of a large area of metal near the imaging area on the imaging result is successfully suppressed. Imaging of a scratch on the plastic substrate makes the new probe feasible for quality identification of nonmetallic cultural relics.

Quantitatively analysis of nonlinear/linear nanofocusing of plasmonic tips array driven via radial vector beam

Electric field enhancement of the plasmonic tip-based nanofocusing light field determines the interaction efficiency of light and matter. Herein, the nonlinear/liner nanofocusing of the plasmonic tips array (PTA) is quantitatively analyzed, under excitation of the radial vector beam (RVB) and the linear polarization beam (LPB), respectively. Second harmonic (SH) emission intensity of PTA, under ultrafast RVB excitation, has been increased 18.6 times than that of the ultrafast LPB excitation. Experimental result is coincided with the theoretical prediction of 20.5 times, revealing that PTA has better nonlinear nanofocusing under excitation of the ultrafast RVB. The linear nanofocusing is examined via surface-enhanced Raman scattering (SERS). Under continuous wave RVB excitation, Raman scattering intensity of 4-Mercaptobenzoic acid (4MBA) is increased 4.5 times than that of LPB excitation, coinciding with the theoretically calculated electric field intensity enhancement of 4.8 times. Furthermore, the linear nanofocusing of PTA is examined using Raman scattering of the monolayer graphene, revealing that the linear nanofocusing of PTA will be slightly deteriorated, when a monolayer graphene is coated on PTA. This method may be adopted as a plasmonic tip-based nanofocusing light field with significant electric field enhancement to increase the light-matter nonlinear/linear interaction efficiency.

Ultralarge Rabi splitting and broadband strong coupling in a spherical hyperbolic metamaterial cavity

Strong coupling (SC) between two resonant plasmon modes can result in the formation of new hybrid modes exhibiting Rabi splitting with strong energy exchange at the nanoscale. However, normal Rabi splitting is often limited to ∼ 50 – 320 meV due to the short lifetime of the plasmon mode. Here, we theoretically demonstrate a record Rabi splitting energy as large as 805 meV arising from the SC between the high- Q plasmonic whispering gallery mode and high- Q cavity plasmon resonance supported by a spherical hyperbolic metamaterial cavity, which consists of a dielectric nanosphere core wrapped in 7 alternating layers of silver/dielectric materials. In addition, the new hybrid modes formed by the SC are shown to exhibit an extralong lifetime of up to 71.9–81.6 fs, with the large electric field intensity enhancement at both the dielectric core and the dielectric layers. More importantly, the spectral ranges of SC can be tuned across an ultrabroad range from the visible to the near-IR by simply changing the dielectric core size. These findings may have potential applications in bright single-photon sources.

Graphene-based tunable hyperbolic microcavity

Graphene-based hyperbolic metamaterials provide a unique scaffold for designing nanophotonic devices with active functionalities. In this work, we have theoretically demonstrated that the characteristics of a polarization-dependent tunable hyperbolic microcavity in the mid-infrared frequencies could be realized by modulating the thickness of the dielectric layers, and thus breaking periodicity in a graphene-based hyperbolic metamaterial stack. Transmission of the tunable microcavity shows a Fabry–Perot resonant mode with a Q-factor > 20, and a sixfold local enhancement of electric field intensity. It was found that by varying the gating voltage of graphene from 2 to 8 V, the device could be self-regulated with respect to both the intensity (up to 30%) and spectrum (up to 2.1 µm). In addition, the switching of the device was considered over a wide range of incident angles for both the transverse electric and transverse magnetic modes. Finally, numerical analysis indicated that a topological transition between elliptic and type II hyperbolic dispersion could be actively switched. The proposed scheme represents a remarkably versatile platform for the mid-infrared wave manipulation and may find applications in many multi-functional architectures, including ultra-sensitive filters, low-threshold lasers, and photonic chips.

Study on mode shifts of localized surface plasmon cavity in Ag nanowire tetramer

The interaction between noble metal nanowires can induce the local surface plasmonic resonance effect, thereby enhancing the distribution of electric field in the nanostructures, which is of very important significance in improving the fluorescence characteristics and enhancing the sensitivity of sensors. In this study, we design several types of tetramers based on precious metals Ag nanostructures, including cylindrical and prismatic Ag tetramers, and by changing the arrangement and the rotation angle of prism nanowires, we simulate the rotation-angle dependent electric field distribution and electric field intensity of &lt;i&gt;X&lt;/i&gt; component , and also discuss the physical mechanism of the relationship between the resonant peak position of absorption spectrum and the change of mode volume. The results show that in the Ag nanowires tetramer structure, the electric field in the cylindrical structure is not enhanced obviously, but the electric field in the prismatic structure is greatly enhanced, and an electric dipole resonance mode is produced in the gap between tetramers. The polarization of plasma resonant cavity revels that the morphology plays a decisive role in generating the hot spots, After changing both the combination mode of tetramer nanowires and the rotation angle of the four-prism, the local surface exciton resonance of the unrotated asymmetric tetramer structure is most ideal and has resonance intensity higher than the that of symmetrical four-prism structure. Therefore, our results provide a structural model and theoretical parameters for the enhancement of electric field intensity by local surface plasmon resonance effect.

Simulation and Fabrication of Nanoscale Spirals Based on Dual-Scale Self-Assemblies.

Archimedean spirals in nanometer scale have shown remarkable plasmonic responses derived from their linear and rotational asymmetry. Despite the unique optical properties of nanoscale spirals, their applications have been limited due to the difficulty in fabricating large-scale arrays with uniform and systematic control of the morphology. Here, we report simulation results of spiral morphologies, which are used to design a scalable fabrication process for nanoscale spirals and predict their plasmonic responses. First, self-consistent field theory (SCFT) simulations were performed to design optimal templates to guide self-assembly into spiral morphologies. Using the SCFT results, we developed a scalable fabrication process, which is based on the micron-scale assembly of microspheres combined with glancing angle deposition and nanoscale assembly of block copolymers, to induce the formation of uniform nanospirals with diverse size, handedness, orientation, and winding number. Finally, finite-difference time-domain simulation results show linear dichroism and electric field intensity enhancement effects of these nanospirals, which are highly dependent on the winding number of the spirals, indicating the importance of precise control of the structural parameters.

Optical trapping of single nano-size particles using a plasmonic nanocavity

Trapping and manipulating micro-size particles using optical tweezers has contributed to many breakthroughs in biology, materials science, and colloidal physics. However, it remains challenging to extend this technique to a few nanometers particles owing to the diffraction limit and the considerable Brownian motion of trapped nanoparticles. In this work, a nanometric optical tweezer is proposed by using a plasmonic nanocavity composed of the closely spaced silver coated fiber tip and gold film. It is found that the radial vector mode can produce a nano-sized near field with the electric-field intensity enhancement factor over 103 through exciting the plasmon gap mode in the nanocavity. By employing the Maxwell stress tensor formalism, we theoretically demonstrate that this nano-sized near field results in a sharp quasi-harmonic potential well, capable of stably trapping 2 nm quantum dots beneath the tip apex with the laser power as low as 3.7 mW. Further analysis reveals that our nanotweezers can stably work in a wide range of particle-to-tip distances, gap sizes, and operation wavelengths. We envision that our proposed nanometric optical tweezers could be compatible with the tip-enhanced Raman spectroscopy to allow simultaneously manipulating and characterizing single nanoparticles as well as nanoparticle interactions with high sensitivity.

Efficiency enhancement in polymer solar cells using combined plasmonic effects of multi-positional silver nanostructures

Abstract Achieving high absorption enhancement in a broad wavelength range without increasing the thickness of active layer is essential for improving the performance of polymer solar cells. In this work, we report efficiency enhancement in poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno [3,4-b]thiophenediyl}): [6,6]-phenyl C71-butyric acid methyl ester active layer based polymer solar cells by incorporating silver nanostructures simultaneously in cathode buffer layer and active layer. Efficiency of the device was increased from 6.53% to 7.53% after incorporating the nanostructures. The plasmonic devices exhibited superior performance in a broad wavelength range from 450 nm to 750 nm. Photoluminescence measurements were carried out to confirm the improvement in light harvesting capability of the devices. Finite-difference time-domain simulations and Raman spectroscopy were employed to verify the electric field intensity enhancement around the nanostructures. The performance enhancement mechanism was realized based on theoretical simulations and optical measurements.

A comparative study among WS2, MoS2 and graphene based surface plasmon resonance (SPR) sensor

In the present paper, we propose a new design of surface plasmon resonance (SPR) sensor having better performance parameters by employing the well-known transfer matrix method. The proposed SPR sensor is comprised of BK-7 prism-ZnO-Ag-BaTiO3-Transition metal dichalcogenides (TMDCs, mainly WS2 and MoS2)/Graphene. A comparison is made among their performance parameters i.e. sensitivity, detection accuracy, quality parameter with other traditional reported SPR sensor. We have also analysed full width at half maxima (FWHM) and electric field intensity enhancement factor (EFIEF) for the proposed SPR sensor. On comparison, it is found that the proposed SPR sensor with monolayer WS2 configuration has better sensitivity of 180°/RIU as compared to monolayer MoS2 and graphene which are 174°/RIU and 157°/RIU respectively. However, the proposed SPR sensor with graphene layer shows small FWHM, higher quality parameter and detection accuracy. We have found that maximum sensitivity of 2350/RIU corresponds to the two-layer WS2 configuration. Our proposed SPR sensor shows better performance as compared to the other reported works.