Strong Magnetic Dipole Research Articles

(Invited) Optical Excitations and Growth in Layered Organic Metal Halide Semiconductors

Hybrid organic metal halides, such as CH3NH3PbI3, have garnered attention because they are earth-abundant, solution-processable materials that can be used to form solar cells with high power conversion efficiency (>20%). There are significant questions about the unusual electronic properties of this class of materials because of the coupling between excitations and the lattice. We will present our work investigating the optoelectronic properties of layered organic metal halide systems and the relationship to structure and growth conditions. We will discuss the nature of optical excitations in layered compounds of the class R2PbX4 where R is an organic cation and X is a halide. These systems show signatures of unusually strong optical frequency magnetic dipole transitions that can be understood through self-trapped exciton formation. We will then discuss how mechanical strain during growth influences broad photoluminescence in a model layered system based on the large cation ethylammonium (EA) with the structure (EA)2(EA)n-1PbnBr3n+1. In this system the emission is strongly impacted by growth-induced strain in thin films quantified using X-ray scattering. Our results suggest that broad emission, relevant for LEDs, can be tuned in thin films. Recent work on how growth impacts the behavior of low dimensional system will also be presented.

Strengthening mechanism of large-diameter magnetic particles on ferrofluid nanoparticle chaining

The magnetization of nano ferrofluid is lower than that of micrometer magnetorheological fluid, which limits its application in seals, dampers, and various other fields. To enhance the ferrofluid performance, this paper incorporates large-diameter magnetic particles into the ferrofluid to strengthen chaining among nanoparticles. A matrix discrete element method model is constructed to investigate the strengthening mechanism of large-diameter magnetic particles on ferrofluid nanoparticle chaining. Additionally, the chain formation process involving both large and small particles and the influence of large particle volume fractions on chain length, particle number, and yield strength are studied based on the simulation. The results show that small particles and large particles together constitute different complex structures, such as the columnar structure and column-net structure under the strong magnetic dipole force of the large particles, leading to the high chain structure strength. In addition, the chain formation speed, average chain length, average particle number, yield strength, and additional viscosity are influenced by the volume fractions and particle sizes of large particles. The method will enhance the ferrofluid sealing performance and expand the ferrofluid application areas.

Enhanced second harmonic generation from supercavity mode and magnetic resonance in dumbbell-shaped silicon nanoblock

Abstract Electromagnetic multipole resonance can be excited by dielectric nanostructures of appropriate size to effectively promote light-matter interaction. The interactions between light and nanostructures have the capability to enhance the electromagnetic field in the near field, thereby improving the nonlinear effect of nanostructures. We illustrate that the supercavity mode and magnetic dipole resonance are activated by a single dumbbell-shaped silicon nanoblock (DS-SiNB), to trap the near-field electromagnetic field energy. Enhanced second harmonic generation is achieved by exploiting the localized electromagnetic field at the surface of the nanostructure. Numerical simulations reveal that magnetic quadrupole (MQ) and total electric dipole (TED) can be coupled to the same radiation channel by adjusting continuously the aspect ratio Lout/Ly (the outer edge length to the length of DS-SiNB) of the nanoblock. When the aspect ratio Lout/Ly = 1, the supercavity mode formed by the interference of MQ and TED is excited at λ1 = 1124 nm. And, the strong magnetic resonance mode formed by the coupling of two magnetic dipoles (MD) in the same direction is also excited at λ2 = 1124 nm. Supercavity mode and strong magnetic dipole resonance can effectively capture electromagnetic fields on the surface of nanostructures to attain enhanced second harmonic generation (SHG). Our study presents a novel approach to enhance the nonlinear optical effect of a single silicon nanostructure, which can lead to the development of more efficient nonlinear optical devices.

Stretchable structural colors with polarization dependence using lithium niobate metasurfaces.

Independently tunable biaxial color pixels, composed of isolated nanosquare dimers, are demonstrated in this study. These pixels are capable of displaying a full range of colors under a linear-polarization dependent reflection mode. The metasurface is constructed by arranging LiNbO3 nanodimers on a PDMS substrate. By exciting a strong magnetic dipole (MD) resonance and effectively suppressing other multipolar resonances using surface lattice resonances, the researchers achieved a single reflection peak with a bandwidth of less than 9 nm and a reflective efficiency of up to 99%. Additionally, the stretchability of the PDMS substrate allows for active and continuous tuning of the metasurface by up to 40% strain, covering almost 150 nm of the visible light spectrum and enabling changes in reflection color. This metasurface holds potential applications in various fields, such as color displays, data storage, and anti-counterfeiting technologies.

Visible Metamaterial Using a Lithium Niobate Nanoring Structure for Stretchable Color Sensing Application

All-dielectric metamaterials present the capability to generate high quality structure colors with outstanding color purity and filtering efficiency. In this study, a visible metamaterial composed of a lithium niobate (LiNbO3) nanoring (LNR) structure on polydimethylsiloxane (PDMS) substrate is proposed. By carefully optimizing geometry configurations, a strong magnetic dipole (MD) resonance is stimulated and other multipole resonances are effectively suppressed with the assistance of surface lattice resonance, and then single reflection peaks are generated with high efficiencies up to 99% and narrow bandwidths smaller than 9 nm. Moreover, benefiting from the stretchable property of the PDMS substrate, LNR metamaterial has the potential to be actively tuned by mechanically changing the period of unit cells and then realizing the reflected color changes. Meanwhile, LNR metamaterial is also sensitive to the change of the ambient environment; the figure of merit can be up to 311.11 RIU–1. It indicates LNR metamaterial possesses potentials in stretchable electronics, color generating, light fidelity (LiFi) filtering, and biochemical sensing applications.

A Single-Step Bottom-up Approach for Synthesis of Highly Uniform Mie-Resonant Crystalline Semiconductor Particles at Visible Wavelengths.

Optically Mie-resonant crystalline silicon nanoparticles have long attracted interest for their unique scattering behaviors. Here, we report a bottom-up nonthermal plasma process that produces highly monodisperse particles, with diameters controllable between 60 and 214 nm, by temporarily electrostatically trapping nanoparticles inside a continuous-flow plasma reactor. The particle size is tuned by adjusting the gas residence time in the reactor. By dispersing the nanoparticles in water, optical extinction measurements indicate colloidal solutions of a particle-based metafluid in which particles support both strong magnetic and electric dipole resonances at visible wavelengths. The spectral overlap of the electric and magnetic resonances gives rise to directional Kerker scattering. The extinction measurements show excellent agreement with Mie theory, supporting the idea that the fabrication process enables particles with narrow distributions in size, shape, and composition. This single-step gas-phase process can also produce Mie-resonant nanoparticles of dielectric materials other than silicon and directly deposit them on the desired substrates.

Structural Colors Based on Diamond Metasurface for Information Encryption

AbstractStructural colors based on dielectric metasurfaces are attractive because of their potential application in next‐generation color printing. However, the commonly used dielectric materials suffer from issues of high light absorption (e.g., Si at blue wavelength) and low resistance to corrosion (e.g., titanium oxide), which greatly limit their application as structural color for information encryption. Here, dielectric‐metasurface‐based structural color constructed on nanocrystalline diamond (NCD) film by using bias enhanced nucleation (BEN) technique is demonstrated. Owing to the formation of highly crystalline diamond by the BEN process, the synthesized NCD film with a thickness of ~500 nm exhibits excellent optical quality with a relatively high refractive index that produces a strong magnetic dipole mode by Mie resonance. To realize the dynamic functionalities of diamond‐metasurface color with high resolution, a periodic array of asymmetric diamond cuboids with high aspect ratio (≈3.1) is fabricated, which produces polarization‐dependent response due to the enhanced Mie resonance. By optimizing the configuration of the diamond‐metasurface system, the color performance is improved with high brightness and a relatively wide gamut. This work demonstrates for the first time that NCD can serve as a robust and highly tunable dielectric platform for application in information encryption.

Chiral metasurface absorbers with tunable circular dichroism in the mid-infrared via phase transition of vanadium dioxide

Chiral metasurface absorbers are vital for many applications such as polarization imaging, CD spectroscopy, and thermal emitters. Herein, we present a chiral metasurface integrated with η-shaped vanadium dioxide (VO2) to achieve dynamic tuning of circular dichroism (CD) in the mid-infrared region. The proposed chiral absorber can achieve near-perfect absorption due to the excitation of strong magnetic dipole (MD) resonance under the illumination of the right-handed circularly polarized (RCP) light, while the absorption is comparably low in the case of the left-handed circularly polarized (LCP) light as the electric dipole (ED) mode associated with the LCP light is weak, thus broadband CD effect with maximum CD of 0.63 can be realized due to the remarkable chiral-selective absorption performances. In addition, the CD value and the absorption peak of the chiral metasurface can be dynamically tuned by changing the volume fraction of the metallic state of VO2, and good CD effect can be maintained even if the structural parameters are significantly altered.

Synthesis and luminescence properties of (Dy3+, Eu3+) ions co-doped double-perovskite Ba2LaNbO6 phosphors

Dy[Formula: see text] and Eu[Formula: see text] ions co-doped double-perovskite Ba2LaNbO6 phosphor was prepared by a high-temperature solid-state reaction method. The effects of ions co-doping concentration onto the crystal structures, surface morphologies and photoluminescence properties of phosphors were elucidated by using X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), and fluorescence spectrophotometer, respectively. The XRD patterns reveal that the crystallization of Dy[Formula: see text] and Eu[Formula: see text] ions co-doped Ba2LaNbO6 was monoclinic phase with space group of C2/m. For the Dy[Formula: see text] ion-doped Ba2LaNbO6 phosphors under an excitation wavelength of 293 nm, the main emission wavelengths are between 460 and 520 nm and 560 and 620 nm, which are due to the 4F[Formula: see text]H[Formula: see text] magnetic dipole transition and the 4F[Formula: see text]H[Formula: see text] super sensitive transition of Dy[Formula: see text] ion, respectively. The concentration quenching effect occurs as the Dy[Formula: see text] ion concentration is 4 mol%. The CIE chromaticity coordinates shift from the light blue region to the green region as the Dy[Formula: see text] ion doping concentration increases. When the Dy[Formula: see text] and Eu[Formula: see text] ions co-doped Ba2LaNbO6 phosphors, the CIE chromaticity coordinates of Ba2(La[Formula: see text] Dy[Formula: see text]Eu[Formula: see text]Nbo6 phosphors are moved from the green light region to the near white-light region due to the mixing of the strong magnetic dipole transition of 5D[Formula: see text]F1 at 594 nm, and electric dipole transition of 5D[Formula: see text]F2 at 617 nm for the characteristic [Formula: see text]–[Formula: see text] transition of Eu[Formula: see text] ion.

Perfect magnetic mirror based on magnetic dipole scattering in all-dielectric resonators

Perfect magnetic mirrors are important optical devices for the development of novel optical detectors, solar cells, and imaging devices. They have the property of only reversing the magnetic field of a light wave upon reflection, for instance, in functional optical metasurfaces. To design an optical magnetic mirror, high-refractive-index dielectric nanostructures that support strong magnetic dipole (MD) response in the optical wavelength range are used. However, the spectral overlap between the MD and electric dipole in dielectric resonators degrades the magnetic mirror reflection. Here, we propose and demonstrate a perfect optical magnetic mirror metasurface that totally reflects an incident wave without electric field phase change. In this perfect magnetic mirror, the electric dipole radiation is completely suppressed by the radiation of the anapole mode in the spectral range where the destructive interference between the electric dipole and toroidal dipole occurs. By fine-tuning the size parameters of the dielectric resonators, we show near-perfect MD scattering as a result of the spectral overlap between MD resonance and anapole mode. The optical magnetic mirror can be tuned from the visible to near-infrared range by scaling the sizes of the resonators. The MD scattering resonators promote the perfect magnetic mirror, a promising platform for designing photodetectors, biological sensors, and reflected waveplates.

Heterogeneity in Dynamic Metamolecules

Here, we fabricated spherical assemblies of metal nanobeads with size or material heterogeneity to study how the mismatch in the strength and energy of surface plasmon resonance (SPR) of nanobead building blocks affects the global magnetic resonance modes. In binary metamolecules (BMMs) composed of 15 and 45 nm Au beads, small 15 nm beads can act as the medium between sparsely placed large nanobeads and enhance the overall plasmon coupling, resulting in a strong and narrow magnetic dipole resonance. In BMMs made of Au and Ag nanobeads of the same size, the coupling between Au and Ag nanobeads significantly contributes to the magnetic resonance modes, affecting both their strength and position, while it does not significantly affect electric modes. These results provide valuable guidelines for the fabrication of colloidal metamolecules with desired metamaterial properties.

Similarity and Finite Difference Solution on Biomagnetic Flow and Heat Transfer of Blood‐Fe3O4 through a Thin Needle

A magnetic fluid is composed of a base fluid and magnetic particles, where magnetic particles are carefully distraught in the base fluid. Here, we will assume that blood is the base fluid that exhibits electrical conductivity and polarization properties and Fe3O4 as magnetic particles. The addition of Fe3O4 into the blood can remarkably ameliorate the properties of the blood’s thermal conductivity. Such physical aspects can play a vital role in biomedical and bioengineering. The presented model studies the biomagnetic fluid flow, such as blood that contains magnetic particles through a thin needle in the appearance of a strong magnetic dipole. First, the governing equations are transformed using similarity transformation into a system of dimensional differential equations, which are then nondimensionalized. The system of nondimensional equations is then solved numerically using a finite difference method. By analyzing the results, we find that the axial flow decreases for the ferromagnetic number, magnetic field number, and Eckert number, while the temperature increases with volume fraction, where the size of the needle plays a significant role. Finally, the results also indicate that the presence of ferromagnetism significantly influences the skin friction coefficient. Our presented results will also be compared with existing literature that is similar to our work.

Tailoring Magnetic Dipole Emission by Broken-Symmetry TiO2 Metasurfaces

Strong magnetic dipole emission is offered by rare earth ions such as trivalent lanthanides, due to selection rule forbidden electric dipole (ED) transitions. This stimulates the study of optical nanostructures, which efficiently tailor magnetic dipole emission. High refractive index all dielectric nanostructures are promising candidates in this regard due to their strong magnetic response and negligible absorption loss in the visible spectral range. Here, we design and experimentally realize a broken-symmetry titanium dioxide (TiO2) metasurface supporting an out-of-plane magnetic dipole (MD) resonance at 590 nm wavelength, corresponding to the MD transition of trivalent Europium ions (Eu3+). A strong photoluminescence (PL) enhancement of the MD transition up to a factor of 15.5 is observed.

Synthesis and characterization of poly(styrene-co-divinylbenzene) and nanomagnetite structures

The use of iron oxide nanoparticles for the synthesis of adsorbents materials with application in contaminated water remediation is based on both their magnetic and adsorption properties. Poly(styrene-co-divinylbenzene) - Poly(Sty-co-DVB)microparticles are widely known for this use and the addition of magnetite comes to add magnetic properties, however it should not limit the functionalization processes for formation of cationic and/or anionic resins. Thus, there is a concern about the stability of magnetite in acidic environments, as required by the sulfonation process, for example. Furthermore, the synthesis of composites with magnetic nanoparticles is a challenge due to the strong magnetic dipole interactions between particles resulting from the high specific surface area, making them susceptible to aggregation. As well as oxidation during the synthesis process can compromise the structure of the initial magnetic material. In this sense, the present work validated processes for the synthesis of Poly(Sty-co-DVB)/magnetite microparticles that sought, as a final result, the incorporation of magnetite aiming to preserve its initial structural conformation. Thus, started from original synthesis method aimed at the production of Poly(Sty-co-DVB) microparticles without magnetite, to methods in which magnetite nanoparticles is added through two distinct processes, different regarding the use or not of oleic acid in its preparation.In this method article we show:•Combination of methods to preserve the structure of magnetite in the Poly(Sty-co-DVB)/magnetite composite.•Simple method of adding magnetite to the Poly(Sty-co-DVB)/magnetite composite synthesis process.•Magnetite treatment method with oleic acid in Poly(Sty-co-DVB)/magnetite composite synthesis.The samples were characterized using Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and Mössbauer spectroscopy to evaluate the chemical modifications that were introduced in the original synthesis method.

Ultrahigh broadband absorption in metamaterials with electric and magnetic polaritons enabled by multiple materials

Large amounts of studies focus on perfect absorption of metamaterials based on electric plasmon resonance. However, it still challenges a lot in total absorption of solar energy with different kinds of plasmon resonances. In this paper, we numerically study the absorption properties of a proposed plasmonic absorber based on a variety of different materials. The proposed plasmonic absorber is composed of a carbon bottom layer, a top layer with different subwavelength nanostructures, as well as a layer of Al2O3 in between. The effects of thickness of different layers, material, height, diameter, and center distance of nanostructures on solar energy harvesting performance are numerically studied. The simulation results show that the proposed absorber exhibits excellent broadband absorption properties, and the absorptance in the wavelength range from 300 nm to 1200 nm is higher than 98.2% or even 100% in a wide wavelength range. It has been demonstrated that the nearly perfect absorption of solar energy originates from both of strong electric dipole resonance and magnetic dipole resonance due to the interaction between nanostructures made of different materials. In addition, the carbon bottom layer also contributes to the broadband absorption of electromagnetic waves. However, the geometric parameters make a big difference on the absorption property of the proposed absorber, though there is a large tolerance for the possible error during the potential fabrication process. Furthermore, the proposed absorber is almost free of the polarization of the light. Therefore, the present study provides a new physical mechanism for designing the nearly perfect absorber for solar energy harvesting submerged in water.

Magnetic toroidal dipole resonances with high quality factor in all-dielectric metamaterial

Meta-photonics with high quality factor (Q-factor) resonances have been proposed as promising candidates for various practical applications. Recently, the theory of bound states in the continuum (BICs) has drawn great attention as it offers a simple method to pursue high Q-factors by exciting supercavity modes in nanostructures. Here, we report a novel optical metamaterial exhibiting sharp Fano-type resonances driven by quasi-BICs. Unit cell of the proposed metamaterial consists of three bars made of intrinsic silicon. The proposed metamaterial supports strong magnetic toroidal dipole (MTD) resonance, which is verified by both the multipole expansion and localized field distribution. Further analyses show that the Q-factor can be easily modulated by tuning the degree of asymmetry and their relationship follows an inverse quadratic law. Owing to its narrow linewidth, the proposed MTD metamaterial can serve as an optical sensing platform for monitoring surrounding refractive index, whose sensitivity and figure of merit (FOM) can reach to 894 nm/RIU and 3.89×103, respectively.

High efficiency and ultra-wideband polarization converter based on an L-shaped metasurface

An ultra-wideband and efficient single layer polarization converting metasurface based on an L-shaped resonator is presented. The metasurface is based on an F4B dielectric substrate with relative permittivity of 2.65 and a loss tangent of 0.002. The size of the unit cell is 0.132λo × 0.132λo and the thickness of the metasurface is 0.05λo, where λo is the largest wavelength (corresponding to the lower frequency) in the operation band of interest. The proposed structure effectively transforms the linearly or circularly polarized incident wave to its orthogonal equivalent, which is justified by both simulated and measured results where the polarization conversion ratio (PCR) is greater than 90% in the frequency range from 8.6 GHz to 22 GHz with a fractional bandwidth of 88%. The polarization transformation process is illustrated in depth by the surface current distribution. Simulation results reveal that ultra-wideband is achieved because of strong electric and magnetic dipole resonances on the upper and the lower layer of the metasurface. Furthermore, the bandwidth and central frequency can be efficiently adjusted over a wide spectrum by changing the geometric aspects of the unit cell, thereby retaining high transformation proficiency. The designed converter can be used in applications such as antenna design, radar invisibility, imaging, microwave communications, and remote sensing.

Electromagnetic response of nanoparticles with a metallic core and a semiconductor shell

We study the interplay between localized surface plasmon resonances from metallic cores and electromagnetic resonances from semiconducting shells in core@shell nanoparticles in the optical and near-infrared regions. To this end, we consider silver (Ag) spheres as plasmonically active nanoparticles with radii 20 nm, covered with shells of silicon (Si) up to 160 nm in thickness. We use the classical Lorenz-Mie theory to calculate the response of the core@shell nanoparticles to an external electromagnetic field that reveals a high degree of tunability of the Ag surface plasmons with a varying Si shell thickness, and a consequent merging of their Mie resonances. In contrast with pure metallic systems, the use of a low-bandgap semiconducting shell allows for a unique interrelation between its strong characteristic magnetic dipole mode and the localized surface plasmon resonance of the metallic core. This allows control over the forward and backward scattering efficiencies in the near-infrared in accordance with the predictions based on the Kerker conditions. Employing several other core@shell materials (Al@Si, Au@Si and Ag@Ge), we show that this approach to tailoring the absorption and scattering efficiencies, based on Kerker’s conditions, can be further generalized to other similar core@shell systems.

MoS2-SiO2/EG hybrid nanofluid transport in a rotating channel under the influence of a strong magnetic dipole (Hall effect)

PurposeThe article focuses on the magnetohydrodynamic (MHD) convective flow of MoS2-SiO2 /ethylene glycol (EG) hybrid nanofluid. The effectiveness of Hall current, periodically heating wall and shape factor of nanoparticles on the magnetized flow of hybrid nanocomposite molybdenum disulfide- silicon dioxide (MoS2-SiO2) suspended in ethylene glycol (EG) in a vertical rotating channel under the influence of strong magnetic dipole (Hall effect) and thermal radiation is assessed. One of the channel walls has an oscillatory temperature gradient. Four different shapes (i.e. brick, cylinder, platelet and blade) of nanoparticles disseminated in base fluid (EG) are considered for simulation of the flow.Design/methodology/approachThe analytical solution of governing equations has been presented. Influences of emerging physical parameters on the velocity and temperature profiles, the shear stresses and the rate of heat transfer are pointed out and discussed via graphs and tables.FindingsThe analysis revealed that Hall parameter has suppressing behavior on the velocity profiles within the rotating channel. The impact of nanoparticle shape factor advances the temperature characteristics significantly in the rotating channel. Brick-shape nanoparticles put up relatively low-temperature distribution in the rotating channel. The Hall parameter reduces the amplitudes of the shear stresses at the channel wall. However, the radiation parameter enhances the amplitude of the rate of heat transfer at the channel wall.Social implicationsThe important technical advantage of hybrid composition of nanoparticles as a drug carrier is its stability, high thermal conductivity, high load carrying capacity, etc. The proposed model may be beneficial in biomedical engineering, automobile parts, mineral and cleaning oils manufacturing, rubber and plastic industries.Originality/valueTo the best of our knowledge, there is little or no report on the aspects of assessment of the effectiveness of Hall current and nanoparticle shape factor on an MHD flow and heat transfer of an electrically conducting MoS2-SiO2/EG ethylene glycol-based hybrid nanofluid confined in a vertical channel with periodically varying wall temperature subject to a rotating frame. The present work furnishes a robust benchmark for the dynamics of nanofluids.

Structure of positive parity states in 139Pm

The excited states of 139Pm is investigated via 127I(16O, 4n)139Pm reaction at 84 MeV beam energy. The spin and parity of several states have been determined from the results of angular correlation (RDCO) and linear polarization asymmetry () measurements. The features of four positive parity bands have been determined. A band above state at 1951 keV comprised of strong magnetic dipole transitions has been established and a three-quasi-protons configuration is suggested on the basis of systematic of neighbouring nuclei. Additionally, a new band above state at 228 keV is observed. The states are compared with the modified particle rotor model calculations which indicated πg7/2 configuration for this band.