FDTD Calculations Research Articles

Tunable Ag Nanocavity Enhanced Green Electroluminescence from SiNx:O Light-Emitting Diode.

As the driving source, highly efficient silicon-based light emission is urgently needed for the realization of optoelectronic integrated chips. Here, we report that enhanced green electroluminescence (EL) can be obtained from oxygen-doped silicon nitride (SiNx:O) films based on an ordered and tunable Ag nanocavity array with a high density by nanosphere lithography and laser irradiation. Compared with that of a pure SiNxO device, the green electroluminescence (EL) from the SiNx:O/Ag nanocavity array device can be increased by 7.1-fold. Moreover, the external quantum efficiency of the green electroluminescence (EL) is enhanced 3-fold for SiNx:O/Ag nanocavity arrays with diameters of 300 nm. The analysis of absorption spectra and the FDTD calculation reveal that the localized surface plasmon (LSP) resonance of size-controllable Ag nanocavity arrays and SiNx:O films play a key role in the strong green EL. Our discovery demonstrates that SiNx:O films coupled with tunable Ag nanocavity arrays are promising for silicon-based light-emitting diode devices of the AI period in the future.

Enhancing external quantum efficiency of deep ultraviolet micro-leds through geometry design and multi-physics field coupling analysis

Abstract High-efficiency deep-ultraviolet (DUV) micro light-emitting diodes (LEDs) are explored for inspiring development in numerous fields, such as non-line-of-sight solar-blind communication, optical pumping, and maskless lithography. In this study, we performed FDTD and SimuLED calculations to investigate the optimized DUV micro-LED structure geometry for high light extraction efficiency (LEE) by designing different mesa structures, including square, hexagonal, and circular geometries of micro-LEDs emitted at a wavelength of 275 nm. The results showed that a circular mesa of 5 μm diameter achieved a LEE of 27% from the bottom and sidewall emissions of as-prepared DUV micro-LED. And both the near- and far-field transverse magnetic polarized light intensities were enhanced by a factor of 1.5 over the square and hexagonal mesas. Meanwhile, the transverse electric (TE) polarized light of the circular mesa structure was enhanced and concentrated along the normal direction. Moreover, the internal quantum efficiency (IQE) of circular mesas with varied sizes was comprehensively investigated in the interactions of the thermal and electric fields. An AlGaN-based DUV micro-LED with a diameter of 5 μm was found to obtain the highest IQE owing to a high current-density distribution and its self-heating properties, thereby achieving a sufficiently high external quantum efficiency of 26.75%. This study provides a comprehensive technical report, including electrical, thermal, and optical analyses, and a new perspective for developing high-efficiency, high-performance DUV micro-LEDs in practical applications.

Formation of two-dimensional diamond-like colloidal crystals using layer-by-layer electrostatic self-assembly.

We report here that a two-dimensional (2D) diamond-like structure of micron-sized colloidal particles can be obtained by layer-by-layer self-assembly. Positively and negatively charged silica particles, 1 μm in diameter, were used in the experiments. On a positively charged, flat glass substrate, the first layer of negatively charged particles was prepared to form a non-close-packed 2D crystal. Then the second and third layers were fabricated using electrostatic adsorption. The positions of adsorbed particles were controllable by tuning the zeta-potential of the particles and the salt concentration of the medium. The FDTD calculations show that the 2D diamond structures of particles with higher refractive index (titania) have an absorption band in the wavelength range corresponding to the photonic band gap of the 3D bulk crystal. We expect these findings to be useful for the fabrication of novel photonic materials.

Bio-inspired hierarchical wrinkles for tunable infrared reflectance

Wrinkles with large infrared emissivity regulation are attractive for thermal management. Here we present the design and preparation of hierarchical wrinkles (H-wrinkles) of POE-POE/Al, which exhibit a high reflectance modulation range from 0.60 to 0.16 upon mechanical actuation. The POE-POE/Al primary wrinkles (P-wrinkles) with optimum structure factors are prepared by hot-pressing. According to the FDTD calculation, the infrared absorption by plasma resonance in periodic structure mainly occurs at the troughs. Hierarchical troughs would further promote the infrared absorption by dual plasma resonance. Then sub-troughs via mechanical instability are introduced in the primary troughs according to prediction of theoretical analysis. When placed on a hot stage of 40°C, a temperature difference of ∼5.3°C is obtained for the H-wrinkles before and after a uniaxial stretching of 150%. Meanwhile, when being covered on the artificial skin, the H-wrinkles could achieve a dynamic temperature modulation of ∼1.4°C upon mechanical actuation. The study offers a strategy for preparation of the biomimetic wrinkles with high infrared modulation ability for applications in infrared camouflage and thermal management.

A Promising Radiation Thermal Protection Coating Based on Lamellar Porous Ca‐Cr co‐Doped Y3NbO7 Ceramic

AbstractDissipation of heat efficiently from a hot object via radiation while minimizing the inward heat conduction is the key requirement of radiation thermal protection. In this study, a Ca‐Cr co‐doped Y3NbO7 coating with lamellar porous structure is fabricated, which shows an ultra‐low thermal conductivity (<0.7 W m−1 K−1) and near‐unity emissivity (>0.9) across a broad wavelength range of ≈1–24 µm. This record high emissivity to thermal conductivity ratio (≈1.3) is experimentally and theoretically revealed from a multi‐scale perspective. The diffusoin‐mediated thermal conduction feature of niobates combined with lamellar porous structure of the coating reduces its thermal conductivity to an impressive 0.5 W m−1 K−1 at 25 °C, surpassing the theoretical amorphous limitation of 0.72 W m−1 K−1. Experiments and FDTD calculation results demonstrate that the intrinsic emissivity dips at shallow extinction wavelengths (1 and 8 µm) and strong phonon‐polariton resonances wavelengths (>13 µm) can be effectively compensated by the multiple scattering/absorption and gradual modulation of conical shape/effective refractive index induced by surface micro‐protrusion structures, respectively. Furthermore, the coating exhibits robust mechanical and thermal stability with a high bonding strength (18.3 MPa) and thermal expansion coefficient (≈11 × 10−6 K−1 at 1200 °C) comparable to YSZ, showing great potential in the radiation thermal protection field.

Optical Control of the Localized Surface Plasmon Resonance in a Heterotype and Hollow Gold Nanosheet.

The remote excitation and remote-controlling of the localized surface plasmon resonance (LSPR) in a heterotype and hollow gold nanosheet (HGNS) is studied using FDTD simulations. The heterotype HGNS contains an equilateral and hollow triangle in the center of a special hexagon, which forms a so-called hexagon-triangle (H-T) heterotype HGNS. If we focus the incident-exciting laser on one of the vertexes of the center triangle, the LSPR could be achieved among other remote vertexes of the outer hexagon. The LSPR wavelength and peak intensity depend sensitively on factors such as the polarization of the incident light, the size and symmetry of the H-T heterotype structure, etc. Several groups of the optimized parameters were screened out from numerous FDTD calculations, which help to further obtain some significant polar plots of the polarization-dependent LSPR peak intensity with two-petal, four-petal or six-petal patterns. Remarkably, based on these polar plots, the on-off switching of the LSPR coupled among four HGNS hotspots could be remote-controlled simply via only one polarized light, which shows promise for its potential application in remote-controllable surface-enhanced Raman scattering (SERS), optical interconnects and multi-channel waveguide switches.

Fabrication and nano-engineering of non-/noble metal-coupled plasmonic heterostructures for ultrasensitive photoelectrochemical immunoassays

To achieve reliable and ultrasensitive detection for disease markers in PEC bioanalysis, constructing and nano-engineering of ideal photoelectrodes and signal transduction strategies are of vital importance. Herein, a non-/noble metal coupled plasmonic nanostructure (TiO2/r-STO/Au) was tactically designed with high-efficient PEC performance. Evidenced by the DFT and FDTD calculations, the reduced SrTiO3 (r-STO) was found to support the localized surface plasmon resonance due to the sufficiently increased and delocalized local charge in r-STO. Under the synergistic coupling of plasmonic r-STO and AuNPs, the PEC performance of TiO2/r-STO/Au was found remarkably promoted with reduced onset potential. This merit supported TiO2/r-STO/Au as a self-powered immunoassay via a proposed oxygen-evolution-reaction mediated signal transduction strategy. With the increase of the target biomolecules (PSA), the catalytic active sites of TiO2/r-STO/Au would be blocked and result in the decrease of the oxygen evaluation reaction. Under optimal conditions, the immunoassays exhibited an excellent detection performance with a LOD as low as 1.1 fg/mL. This work proposed a new type of plasmonic nanomaterial for ultrasensitive PEC bioanalysis.

Hybridization of surface lattice modes: towards plasmonic metasurfaces with high flexible tunability

Abstract When assembled in periodic arrangements, metallic nanostructures (NSs) support plasmonic surface lattice (SL) resonances resulting from long-range interactions these surface lattice resonances differ radically from localized surface plasmon (LSP). Similarly to the hybridization of LSP resonances, observed in short-range interactions, we demonstrate the possibility to generate a hybridization of surface lattice (SL) plasmon resonances, by the excitation of grazing order diffraction within the metasurface. This hybridization leads to the emergence of bonding and anti-bonding modes. If hybridization of LSP modes has been widely described in recent literature, there is still no experimental proof-of-concept reporting such hybridization with SL plasmon resonances. We fill this gap in the present paper by considering surfaces made of binary arrays with unit cells made of two gold disks of distinct diameters. We demonstrate the possibility to maximize or cancel the interaction between the hybridized SL resonances by simply controlling the distance between particles. All our experimental results are supported by FDTD calculations. The hybridization of SL modes results in much richer hybridization scenario in terms of wavelength and quality factor control, compared to a hybridization of LSP in a short-range configuration. It offers unprecedented opportunities to generate innovative optical devices, with high flexible tunability.

Towards improved efficiency of SnS solar cells using back grooves and strained-SnO2 buffer layer: FDTD and DFT calculations

In this work, a novel SnS thin-film solar cell (TFSC) based on strained-SnO2 electron transport layer (ETL) combined with back grooves aspect is proposed. The density functional theory (DFT) is used to assess the influence of the unit cell volume engineering on the electronic and optical properties of SnO2 material. Simulated results demonstrate the potential of strained-SnO2 material as a junction partner of p-type SnS absorber, showing a favorable conduction band offset and thereby reduced recombination effects. Moreover, the role of back grooves texture in enhancing light-scattering effects is investigated using FDTD technique. It is revealed that the proposed SnS TFSC based on combined strained-SnO2/SnS heterostructure and optimized back grooves paradigm offers the possibility for bridging the gap between improved absorption capabilities and enhanced photo-induced carrier extraction characteristics. It is demonstrated that the optimized SnS TFSC exhibits superior performances compared to the conventional one in terms of photovoltaic parameters, offering a high short-circuit current of Isc = 28 mA/cm2, a superior open-circuit voltage of Voc = 0.47 V, a high fill factor of FF = 68.4% and over than 9% of PCE. Therefore, our work paves the way to use the strained-SnO2 buffer layer and back grooves to boost the poor performances of SnS-based TFSCs.

Tuning of the plasmon resonance location in Au nanostructures coated with a ultrathin film of Al2O3 – Optical measurements and FDTD simulations

The Au nanostructures have been coated with an ultra-thin films of amorphous aluminium oxide. Optical absorption spectra show the influence of the thickness of Al2O3 on plasmon resonance wavelength. The observed red-shift of the resonance location with the increase of the thickness of the Al2O3 film, can be explained by the change in the dielectric function of this film. It allows control of the optical spectra of the coated particles. In this paper we present a two ways for determinaton of optical paramaters of aluminium oxide ultra-thin films. The first one is based on a ellipsometry method, while in second approach a shift of plasmon resonance is used for computer simulations of films. The experimental data are in agreement with the results of the FDTD calculations, showing the possibility of both determining such a function for ultra-thin layers by the computer simulation method, as well as predicting the value of the dielectric constant depending on the thickness of the layer. The experimental data needed for the simulation was obtained in studies such as XRD, XPS, SEM and HR TEM. The proposed models can help to adjust the coating thickness to the desired plasmon resonance position.

Mass producible, robust SERS substrates based on metal film on nanosphere (MFON) on an adhesive substrate for detection of surface-adsorbed molecules and their evaluation by helium ion microscopy.

We have developed a SERS stamp that can be pressed directly onto a solid surface for characterization of surface-adsorbed target molecules. The stamp was fabricated by transfer of a dense monolayer of SiO2 nanospheres from a glass surface onto a piece of adhesive tape and subsequent evaporation of silver. The performance of the resulting SERS stamps was evaluated by their exposure to methyl mercaptan vapor, and immersion in rhodamine 6G and ferbam solutions. It was found that beside the nanosphere diameter and metal deposition thickness, the extent of burial of the nanospheres into the adhesive tape, dictated by the pressure during the nanosphere transfer process, had a significant effect. We carried out FDTD calculations of the near field. Models are based on morphological information obtained from helium ion microscopy, which can provide high-resolution images of poor electrical conductors such as our SERS stamp. While one of our main eventual goals is detection of pesticides on agricultural produce, we have begun to take a careful step by testing our SERS stamp on better characterized surfaces such as a porous gel surface, having been immersed in fungicides such as ferbam. We also present our preliminary results with ferbam on oranges. It is expected that our well-characterized SERS stamp will play a role in shedding light on the poorly studied transfer process of target molecules onto a SERS surface as well as serving as a new SERS platform.

High-speed FDTD calculation method specialized for automotive radar analysis

High-speed FDTD calculation method specialized for automotive radar analysis

Q-BOR–FDTD method for solving Schrödinger equation for rotationally symmetric nanostructures with hydrogenic impurity

An efficient method inspired by the traditional body of revolution finite-difference time-domain (BOR-FDTD) method is developed to solve the Schrödinger equation for rotationally symmetric problems. As test cases, spherical, cylindrical, cone-like quantum dots, harmonic oscillator, and spherical quantum dot with hydrogenic impurity are investigated to check the efficiency of the proposed method which we coin as Quantum BOR-FDTD (Q-BOR-FDTD) method. The obtained results are analysed and compared to the 3D FDTD method, and the analytical solutions. Q-BOR-FDTD method proves to be very accurate and time and memory efficient by reducing a three-dimensional problem to a two-dimensional one, therefore one can employ very fine meshes to get very precise results. Moreover, it can be exploited to solve problems including hydrogenic impurities which is not an easy task in the traditional FDTD calculation due to singularity problem. To demonstrate its accuracy, we consider spherical and cone-like core-shell QD with hydrogenic impurity. Comparison with analytical solutions confirms that Q-BOR–FDTD method is very efficient and accurate for solving Schrödinger equation for problems with hydrogenic impurity

Surface-Enhanced Raman Scattering on Silver Sinusoidal Nanograting: Impact of Interactions of Grating-Coupled Surface Plasmon Polaritons

In this study, we reported a silver sinusoidal nanograting used in microchannels, forming H2O/Ag/NOA/SiO2 heterostructure and studied the impact of interactions of grating-coupled surface plasmon polaritons (SPPs) on surface-enhanced Raman scattering (SERS). There are two modes of \(E_{x} (z)\) in the Ag grating, namely, the anti-symmetric mode (AM) at the high SPP resonance frequency and the symmetric mode (SM) at the low-SPP resonance frequency. When the refractive indices of the upper and lower dielectrics of the thin Ag grating are close, there will be a strong coupling between the SPPs of the two interfaces, which will increase the transmittance but reduce the maximum electromagnetic (EM) of the SERS substrate. Additionally, the thinner the Ag grating, the stronger the coupling, accompanied by the frequency shift of the two coupling modes. Our experimental results are supported by FDTD calculations, which have corroborated the importance of the interactions of grating-coupled SPPs in the design of SERS substrate.

High performance for refractive index sensors via symmetry-protected guided mode resonance.

The symmetry breaking in a typical dielectric GMR-grating structure allows the coupling of the incident wave with the so-called Symmetry-Protected Modes (SPM). In this present work, the excitation conditions of such particular modes are investigated. A parametric study including the grating dimensions is carried out to exploit them for a blood refractive index sensing with higher Sensitivity (S) and Figure Of Merit (FOM). To our knowledge, the performances obtained by FDTD calculations (Q = 2.1 × 104, S = 657 nm/RIU and FOM ≃ ~9 112 RIU-1) and FMM calculations (Q = 3 × 106, S = 656 nm/RIU and FOM ≃ ~1.64 × 106 RIU-1) are the highest level reached.

Representation of Vivid Colors of Cyan, Magenta, Yellow, and Green in Ag Deposition-Based Plasmonic Electrochromic Device By Precise Control of Shape and Density of Deposited Ag Nanoparticles

Ag nanoparticles exhibit various colors depending on their localized surface plasmon resonance (LSPR). Based on this phenomenon, Ag deposition-based electrochromic devices can represent various optical states in a single device such as the three primary colors (cyan, magenta, and yellow), silver mirror, black and transparent.1 A control of the morphology of Ag nanoparticles can lead to dramatic changes in color, as their size and shape influence the LSPR band. For this purpose, the “voltage-step method” was applied to a Ag deposition-based EC device to obtain multiple colors by shifting the LSPR band. In this method, two different voltages are successively applied : the first voltage V 1 is applied for a very short time t 1 to initiate Ag nucleation, and the second voltage V 2 is applied for a time t 2 to promote growth of the Ag nuclei. As V 2 is more positive than the nucleation voltage, further nucleation is no longer possible during t 2. Therefore, the Ag nanoparticle growth and the resultant device color can be controlled by changing t 2.In this study2, we aimed to improve the color quality of Ag deposition-based multicolor EC devices by precisely controlling the supply of Ag+ ions to the electrode surface. Initially, the effect of coloration by decreasing the concentration of Ag+ ions in the Ag deposition-based EC device was investigated. As a result of optimizing the driving voltage, a lower concentration device (10 mM Ag+ ion) showed vivid and bright colors of cyan and magenta. This improvement was due to the generation of fine Ag nanoparticles and the prevention of the connection of Ag particles. From the electrochemical investigation, it was suggested that the slow supply rate of Ag+ ions in the lower concentration device induced electrochemical deposition of fine and isolated Ag nanoparticles.Consequently, to obtain more uniformly deposited Ag nanoparticles, the nucleation voltage of V 1 was set to a lower voltage in the 10 mM device. As a result, spherical Ag nanoparticles were successfully obtained, and the device showed yellow and green colors. By comparing the LSPR behavior of the device with that of Ag nanoparticles dispersed in solution and using FDTD calculations, the mechanism of the yellow and green colors was investigated in detail. Thus, it indicated that the yellow coloration with an absorption band in the 400–500 nm region was caused by LSPR absorption of isolated spherical Ag nanoparticles. Furthermore, it was also observed that the coexistence of isolated spherical particles and aggregations of Ag nanoparticles induced two types of LSPR bands, leading to a good green color. References A.Tsuboi, K.Nakamura and N.Kobayashi, Chem. Mater., 2014, 26, 6477-6485S.Kimura, T.Sugita, K.Nakamura and N. Kobayashi, Nanoscale, 2020 (in press)

Specular-reflection photonic hook generation under oblique illumination of a super-contrast dielectric microparticle

The possibility of overcoming the critical condition for localized photonic nanojet (PNJ) upon plane optical wave diffraction at mesoscale dielectric particle, which is commonly known as ‘the refractive index contrast is less than two’, was recently reported in our works. To this end, the novel geometrical scheme of PNJ generation in ‘reflection mode’ was proposed recently based on a super-contrast microparticle placed near a flat mirror. In this paper, through the numerical FDTD calculations of optical near-field structure of 2D and 3D dielectric microparticles (cylinder, sphere) we extend our considerations to the case of oblique particle-at-mirror illumination and present new physical phenomena arising in the considered photonic geometry. Specifically, we report on the generation of a quasi-retrograde PNJ which follows the inclined particle illumination and propose a new principle for obtaining a curvilinear photonic flux in the form of a ‘specular-reflection photonic hook’ (s-Hook) in the opposite to the illuminated wavevector direction. Two different regimes of s-Hook formation are analyzed by changing the direction of light incidence on a dielectric particle and by flat mirror inclination. Self-bending property of PNJ at oblique illumination is investigated.

Surface Enhanced Raman Scattering on Regular Arrays of Gold Nanostructures: Impact of Long-Range Interactions and the Surrounding Medium.

Long-range interaction in regular metallic nanostructure arrays can provide the possibility to manipulate their optical properties, governed by the excitation of localized surface plasmon (LSP) resonances. When assembling the nanoparticles in an array, interactions between nanoparticles can result in a strong electromagnetic coupling for specific grating constants. Such a grating effect leads to narrow LSP peaks due to the emergence of new radiative orders in the plane of the substrate, and thus, an important improvement of the intensity of the local electric field. In this work, we report on the optical study of LSP modes supported by square arrays of gold nanodiscs deposited on an indium tin oxyde (ITO) coated glass substrate, and its impact on the surface enhanced Raman scattering (SERS) of a molecular adsorbate, the mercapto benzoic acid (4-MBA). We estimated the Raman gain of these molecules, by varying the grating constant and the refractive index of the surrounding medium of the superstrate, from an asymmetric medium (air) to a symmetric one (oil). We show that the Raman gain can be improved with one order of magnitude in a symmetric medium compared to SERS experiments in air, by considering the appropriate grating constant. Our experimental results are supported by FDTD calculations, and confirm the importance of the grating effect in the design of SERS substrates.

Parallel Implementation of Yee Algorithm 2D Using MPI

The examination work clarifies a practical, superior registering stage for the parallel usage of the FDTD calculation on PC bunches utilizing the message-passing interface (MPI) library, which is a neighborhood framework comprising of various interconnected (PCs), and is now generally utilized for parallel figuring. In this paper, we describe the essential elements of a parallel algorithm for the FDTD method using the MPI (message passing interface). At present, the Internet of Things (IoT) has attracted more and more researchers’ attention. Parallel FDTD method is applied to analyze the electromagnetic problems of the electrically large targets. This paper presents the concept of “the optimum virtual topology” for MPI based parallel FDTD. Parallel FDTD method is applied to analyze the electromagnetic problems of the electrically large targets on super computer.

Enhancement of Magneto-optic Kerr effect of YIG nanoparticle by backscattering suppression

Magneto-optic Kerr effect (MOKE) enhancement is studied for Yttrium Iron Garnet (YIG) nanoparticle. The MOKE is quantified by the ratio of the polarization components of reflected wave, namely between the perpendicular component to the parallel component with respect to the polarization of the incident wave. Thus, the enhancement of MOKE can be obtained by increasing the perpendicular component or reducing the parallel component of the reflected wave polarization. An FDTD calculation is performed to obtain the scattered field. Projecting the resulting scattered field to the vector spherical harmonic basis, we show through multipole moments analysis that the suppression of backscattering non-MO field and the raise of the backscattered MO field can be achieved by subtle superposition of some optical modes. For the specific YIG particle system and the wavelength range chosen, the result shows that enhancement of MOKE up to 7.5[Formula: see text]mrad can be achieved.