Dielectric Core Research Articles

Superior discharge energy density and efficiency in polymer nanocomposites induced by linear dielectric core–shell nanofibers

Novel SrTiO3@Al2O3/PVDF composite film capacitors have remarkably large discharge energy density (15.3 J cm−3) along with high discharge efficiency (68.52%) and ultrafast discharge speed (127 ns).

Highly tunable multiple narrow emissions of dyed dielectric-metal core–shell resonators: towards efficient fluorescent labels

We report a potential efficient fluorescent label based on the dyed dielectric-metal core–shell resonators (DMCSRs). By utilizing the near-field coupling between the dyes and the multipolar sharp cavity plasmon resonances, the dyed DMCSRs with diameter of 1.02 μm are demonstrated to be capable of supporting multiple spontaneous emission peaks with the linewidths as narrow as ∼ 10 nm in visible range, and these reshaped fluorescent emissions are insensitive to the surrounding dielectric environment. Furthermore, these multiple narrow emission peaks show a precise tunability on the spectrum by simply separating a nanometric dielectric layer between the dielectric core and the metallic shell, which may provide an attractive spectral multiplexing strategy in the fields of cell biology and medical sciences.

Synthesis of core–shell structured tetra-needle ZnO whisker and Fe composite with excellent electromagnetic properties

Core–shell structured T-ZnOw@Fe composite composed of a dielectric T-ZnOw core and a ferromagnetic Fe shell was synthesized using MOCVD method. Rough α-Fe shell was homogeneously deposited on the surface of T-ZnOw. The as-prepared composite exhibits excellent microwave absorption properties with the minimum reflection loss (RL) of −55.6 dB for a thickness of 1.48 mm and the broadest effective absorption bandwidth (less than −10 dB) of 4.56 GHz for a thickness of 1.55–1.66 mm. The enhanced electromagnetic performances are attributed to the enhanced interfacial polarization, natural resonance, and exchange resonance. The results imply that the deposition of α-Fe shell on T-ZnOw was an efficient way to fabricate lightweight and high-performance microwave absorption materials.

Optimized cloaks made of near-zero materials for different-sized concealed targets

The optimized cloaking design for conducting cylinders of different sizes is studied based on the Mie scattering theory. We construct a concentric multi-layered cloak made of alternating materials with isotropic dielectrics and epsilon-near-zero (ENZ) material, the thickness of which can be determined through genetic algorithm. As the radius of the conducting cylinder increases, high order scattering contributions are becoming evident, and more layers are needed. The scattering cross sections of three different radii of PEC cylinders are minimized by utilizing different numbers of multi-layers respectively. We find that eight or less optimized layers can cancel most of the scattering from a conducting cylinder with its dimension compared to wavelength, and more effectively when taking the ENZ material as the inner starting shell. The frequency dependence of total scattering is also studied, leading to the result that the bandwidth decreases as the size of concealed PEC cylinder increases. Furthermore, it is shown that the cloaking efficiency is less sensitive to the permittivity and thickness of the ENZ material, due to the small phase variation in the ENZ material. The multi-layered cloak designed for a PEC target can also be used to evidently reduce the scattering of a dielectric core and design a multi-layered elliptical cloak.

Additively Manufactured Profiled Conical Horn Antenna With Dielectric Loading

The world's first additively manufactured dielectric loaded profiled conical horn antenna is presented in this letter. With a smooth profiled flare and two loaded dielectric core materials, this horn offers symmetrical patterns, wideband gain, low sidelobe level, and low cross polarization. Additive manufacturing, including electroplating, has been employed to address the fabrication challenges. The measurement results show that the fabrication process produces a horn antenna with reduced mass and volume (<200 g with three-dimensional-printed flange) and high antenna performance with realized gain 16–20 dBi, sidelobe level −22 to −19 dB across the frequency range from 9 to 15 GHz.

Depolying Tunable Metal-Shell/Dielectric Core Nanorod Arrays as the Virtually Perfect Absorber in the Near-Infrared Regime.

In this paper, the coupled Ag-shell/dielectric-core nanorod for sensor application is investigated and the different dielectric core plasmonic metamaterial is adopted in our design. The operational principle is based on the concept of combining the lattice resonance, localized surface plasmon resonance (SPR), and cavity plasmon resonance modes within the nanostructure. The underlying mechanisms are investigated numerically by using the three-dimensional finite element method and the numerical results of coupled solid Ag nanorods are included for comparison. The characteristic absorptance/reflectance peaks/dips have been demonstrated to be induced by different plasmonic modes that could lead to different responses required for plasmonic sensors. A nearly perfect absorptance and an approximate zero reflectance with a sharp band linewidth are obtained from the proposed system, when operated as an SPR sensor with the sensitivity and figure of merit of 757.58 nm/RIU (RIU is the refractive index unit) and 50.51 (RIU–1), respectively. Our work provides a promising method for the future developments of more advanced metamaterial absorber for chemical sensing, thermal radiation tailoring, field enhanced spectroscopy, and general filtering applications.

Light control based on unidirectional scattering in metal–dielectric core–shell nanoparticles

We theoretically investigate the light control performances of metal−low-permittivity (LP)−high-permittivity (HP) core–shell nanoparticles (M-LP-HP CSNPs). We demonstrate that a free-standing M-LP-HP CSNP can simultaneously possess the zero-backward (ZB) and near-zero-forward (NZF) scattering at different wavelength ranges due to the interference of electric and magnetic modes. We show that at the wavelength of the ZB and NZF scattering, the ability of CSNPs to confine the optical fields within the cavity is quite robust against the existence of LP substrates. As a result, such unidirectional scattering properties are well maintained when the CSNP is placed on the LP substrate. Furthermore, we demonstrate that in the arrays of CSNPs, the high reflection and transmission can be achieved near the wavelengths of NZF and ZB scattering. Particularly for the case of the optimal inter-particle distance, the reflectance can reach 98% over a wavelength range from 868 nm to 935 nm. These features are further tuned to other wavelengths by varying the structural parameters of the CSNPs.

Transient laser-induced voltaic response in a partially illuminated dielectric core

Ultraviolet laser-induced voltage (LIV) measurements were performed on dielectric rock cores. The LIV response in the dielectric core samples were measured with the laser spot partially irradiated at the surfaces under a bias of 210 V, and the accumulation of interface charges was considered resulting in the transient voltage response. The voltage waveforms at the shale and sandstone were different in maximum values (Vp) and full width at half maximum in accordance with the components and structures. Vp, as a function of spot position, depended on the distance between the laser spot and the electrode planes. In addition, ablation was observed in the rock surface irradiated by the pulsed laser, which was associated with rapid buildup of electrons and generation of intrinsic defects in the cores. Therefore, the LIV method can promote the understanding of the interaction between intense laser and dielectric materials.

TM01mode in a cylindrical hybrid plasmonic waveguide with large propagation length

This study reports on a cylindrical hybrid plasmonic waveguide (CHPW) consisting of a high-index dielectric core, a sandwiched low-index dielectric layer, and a metal cladding. The CHPW supports the TM01 mode with a radially polarized transverse component of the electric field. Optical fields can be significantly enhanced in the sandwiched low-index dielectric region with nanoscale thickness down to 5nm, and tight mode confinement with the same order of the normalized mode area compared with that of the plasmonic waveguide is achieved. Moreover, the mode propagation loss is well compensated by adjusting dimensions of the waveguide to obtain a longer propagation distance. The calculated figure of merit reaches a value several times greater than that in the similarly reported structure. The results indicate that this novel type of hybrid structure can support the limited propagation of a radially polarized mode with good confinement and low loss, consummate the whole system of manipulating the cylindrical vector beams, and show great potential of applications for various integrated nano-photonic devices.

Scattering Properties of Individual Hedgehog Particles

“Hedgehog” particles (HPs) possess a micrometer-sized dielectric spherical core which is densely coated with nanoscale metal oxide spikes. This unique surface topography, resembling the appearance of a hedgehog, provides the particles with the exclusive physiochemical property to stably disperse in both polar and nonpolar solvents without the necessity of changing the surface chemistry. Optical extinction measurements of HP ensembles in aqueous solution indicate a broad spectral response in the visible range. However, there remains a dearth of fundamental knowledge about the cause of the broad optical resonance, as it can be a consequence of shape polydispersity in the many-particle system or intrinsic to each individual HP. In this paper, we present the first experimental study of the dark-field scattering of individual hydrophilic and hydrophobic HPs. Our measurements disclose that the expansive optical response in the visible spectral range is truly characteristic for the far-field scattering of a single HP. Our results also uncover how intrinsic particle features, such as spike length, as well as environmental changes affect the scattering of individual HPs. In particular, by changing the atmosphere around a hydrophilic HP from air to nitrogen and by completely immersing in water by employing a 3D optical trap, we discovered that the scattering from a hydrophilic HP is strongly modulated by excess water in its interstitial shell.

3D printed utility dielectric core manufacturing process for antenna prototyping

A prototyping method for dielectrically loaded antennas is presented. Dielectric loading has been used with horn antennas, feeds, and lenses. Dielectrics have also been used for coating antennas submerged in water and biological matter and have led to improvements in bandwidth and efficiency as well as antenna miniaturisation. The authors present a new technique to produce variable dielectrics with permittivity from 6 to 28 using two commonly available powders, titanium dioxide (used in foods) and magnesium silicate (used in talcum powder). An example spherical helical ball antenna is used to demonstrate the process. In this antenna, the mixed powders were encased in a 3D printed shell that achieved a reduction in diameter of the spherical antenna by a factor of 1.85. The technique aids rapid prototyping and optimisation using search algorithms.

Study of plasmonics in hybrids made from a quantum emitter and double metallic nanoshell dimer

We developed a theory for the fluorescence (FL) for quantum emitter and double metallic nanoshell dimer hybrids using the density matrix method. The dimer is made from two identical double metallic nanoshells, which are made of a dielectric core, a gold metallic shell and a dielectric spacer layer. The quantum emitters are deposited on the surface of the spacer layers of the dimers due to the electrostatic absorptions. We consider that dimer hybrids are surrounded by biological cells. This can be achieved by injecting them into human or animal cells. The surface plasmon polaritons (SPP) are calculated for the dimer using Maxwell’s equations in the static wave approximation. The calculated SPP energy agrees with experimental data from Zhai et al (2017 Plasmonics 12 263) for the dimer made from a silica core, a gold metallic nanoshell and a silica spacer layer. We have also obtained an analytical expression of the FL using the density matrix method. We compare our theory with FL experimental data from Zhai et al (2017 Plasmonics 12 263) where the FL spectrum was measured by varying the thickness of the spacer layer from 9 nm to 40 nm. A good agreement between theory and experiment is found. We have shown that the enhancement of the FL increases as the thickness of the spacer layer decreases. We have also found that the enhancement of the FL increases as the distance between the double metallic nanoshells in the dimer decreases. These are interesting findings which are consistent with the experiments of Zhai et al (2017 Plasmonics 12 263) and can be used to control the FL enhancement in the FL-based biomedical imaging and cancer treatment. These interesting findings may also be useful in the fabrication of nanosensors and nanoswitches for applications in medicine.

Dispersion relation and electron acceleration in the combined circular and elliptical metallic-dielectric waveguide filled by plasma

Two special types of metallic waveguide having dielectric cladding and plasma core including the combined circular and elliptical structure are studied. Longitudinal and transverse field components in the different regions are obtained. Applying the boundary conditions, dispersion relations of the electromagnetic waves in the structures are obtained and then plotted. The acceleration of an injected external relativistic electron in the considered waveguides is studied. The obtained differential equations related to electron motion are solved by the fourth-order Runge-Kutta method. Numerical computations are made, and the results are graphically presented.

Acoustic Vibrations of Core–Shell Nanospheres: Probing the Mechanical Contact at the Metal–Dielectric Interface

The acoustic vibrations of metal–dielectric core–shell nanoparticles (Ag@SiO2 and Au@SiO2) are investigated using ultrafast pump–probe spectroscopy. The experimental results are in good agreement with calculations of the period of the breathing vibration of the core–shell particles. The transition from one overtone of the breathing mode to the next one as the size of the silica shell increases is observed for slightly thinner SiO2 shells than previously reported. Our results confirm that this optical technique permits the determination of the quality of the mechanical contact at the metal dielectric interface. This is of major importance for many applications, in particular because it modifies significantly the thermal conductivity at the nanoscale. Moreover, we observed that for two different synthesis routes, poor contact core–shell samples could sneak in among good sample series based on the same metallic core particles. This confirms the suitability of this all optical and noninvasive technique to obt...

Controlling Magnetic Dipole Resonance in Raspberry-like Metamolecules

Raspberry-like metamolecules (RMMs), clusters of closely packed noble metal nanobeads self-assembled on a dielectric core, exhibit emergent optical properties not available in simple nanoparticles. Examples include broad band far-field extinction and artificial optical magnetism. An important feature of these clusters is that their magnetic plasmon resonance and the breadth of their extinction spectra can be tuned via simple synthetic routes, such as by changing the bead size, core size, or the average interbead distance. However, the effect of each of these variables on the final magnetic resonance frequency and strength has not been studied in depth. Understanding how to tune the electric and magnetic resonance modes in these clusters can help improve the design of novel metamaterials for various applications. In this article, we combine theoretical analyses using numerical finite-different time-domain modeling and analytical dipole–dipole coupling theory to study the role of these variables in the glob...

Scattering of electromagnetic waves by a graphene-coated thin cylinder of left-handed metamaterial

In this paper, we explored the scattering behavior of thin cylinders made of a left-handed material (LHM) and coated by a monoatomic graphene layer. A spectral tunability of the resonance peaks is evidenced by altering the chemical potential of the graphene coating, a fact that occurs at any state of polarization of the incident plane wave in opposition to the case of scatterers of dielectric core. On the contrary, no invisibility condition can be satisfied for dielectric environments. A singular performance is also found for cylinders with permittivity and permeability near zero. Practical implementations of our results can be carried out in sensing and wave manipulation driven by metamaterials.

Reconstructing Fine Details of Small Objects by Using Plasmonic Spectroscopic Data. Part II: The Strong Interaction Regime

This paper is concerned with the inverse problem of reconstructing a small object from far field measurements by using the field interaction with a plasmonic particle which can be viewed as a passive sensor. It is a follow-up of the work [H. Ammari et al., Reconstructing fine details of small objects by using plasmonic spectroscopic data, SIAM J. Imag. Sci., to appear], where the intermediate interaction regime was considered. In that regime, it was shown that the presence of the target object induces small shifts to the resonant frequencies of the plasmonic particle. These shifts, which can be determined from the far field data, encodes the contracted generalized polarization tensors of the target object, from which one can perform reconstruction beyond the usual resolution limit. The main argument is based on perturbation theory. However, the same argument is no longer applicable in the strong interaction regime as considered in this paper due to the large shift induced by strong field interaction between the particles. We develop a novel technique based on conformal mapping theory to overcome this difficulty. The key is to design a conformal mapping which transforms the two particle system into a shell-core structure, in which the inner dielectric core corresponds to the target object. We show that a perturbation argument can be used to analyze the shift in the resonant frequencies due to the presence of the inner dielectric core. This shift also encodes information of the contracted polarization tensors of the core, from which one can reconstruct its shape, and hence the target object. Our theoretical findings are supplemented by a variety of numerical results based on an efficient optimal control algorithm. The results of this paper make the mathematical foundation for plasmonic sensing complete.

Gap-Dependent Localized High Energy Multiple Dipolar Modes in Passive Silver-Coated Silica Nanoparticle Antennas

The gap-induced plasmonic response of metallic nanoparticles drastically changes the near and far-field properties of nanoparticle antenna. Similar to a pair of metallic nanostructures, the two nanoparticles, with a dielectric core and silver shell in close proximity, exhibit multiple high energy plasmonic resonances at the short wavelength end of their optical spectrum. In this article, we have overwhelmingly investigated the disparity in the electric field of a core–shell dimer antenna when the gap between nanoparticles within the dimer becomes sub-nanometer in length. We used an electromagnetic planewave to excite the core–shell nanoparticles within the dimer. Frequency domain Finite Element Method (FEM) was employed for the numerical optical analysis of a dimer comprised of two silver-coated silica (SCS) nanoparticles in close proximity, using Computer Simulation Technology (CST) Microwave Studio. A modified Drude model has been used to predict the optical properties of the system with incorporating the size effects. The SCS dimer was numerically analyzed in the visible frequency band, and anomalies in near-field plasmonic coupling were investigated in detail. The inter-surface gap g between nanoparticles within the dimer varied in a range from 0.1 to 402 nm.

Toroidal dipole-induced absorption and scattering dip in (dielectric core)@(plasmonic shell) nanostructures

As the counterpart of electric and magnetic dipoles, the toroidal dipole is of paramount importance in the flourishing fields of metamaterials and Nanophotonics, and has therefore been getting much attention recently. Here, we demonstrate that a toroidal dipole can be formed in (dielectric core)@(plasmonic shell) nanostructures as the core refractive index is increased. For nanostructures with relatively large core refractive indices, polarized charge oscillation can be induced in the core by the oscillation of free electrons in the shell. These two oscillations create a toroidal dipole in the nanostructure. The formation of a toroidal dipole induces a scattering dip and a new absorption peak spectrally close to the created scattering dip. We also show that the toroidal dipole-induced absorption and scattering dip become weaker as the imaginary part of the core refractive index is increased. To the best of our knowledge, this is the first observation that the absorption becomes weaker with the increase of the imaginary part of the refractive index. Moreover, because almost all of the electric and magnetic fields are concentrated within the nanostructure, the toroidal dipole-induced scattering dip and absorption peak show resonance wavelength that is independent of the refractive index of the surrounding medium. Such an invariable property can be used as optical references or marks.

Effective electromagnetic properties of microheterogeneous materials with surface phenomena

In this paper, we present an approach to calculate the complex dielectric permittivity of a micro-heterogeneous medium composed of non-conductive solid inclusions embedded into the conductive liquid continuous host. To take into account the surface effects, we approximate the inclusion by a layered ellipsoid consisting of a dielectric core and an infinitesimally thin outer shell corresponding to an electrical double layer (EDL). To predict the effective complex dielectric permittivity of materials with a high concentration of inclusions, we have modified the Effective Field Method (EFM) for the layered ellipsoidal particles with complex electrical properties. We present the results of complex permittivity calculations for the composites with randomly and parallel oriented ellipsoidal inclusions. To analyze the influence of surface polarization, we have accomplished modeling in a wide frequency range for different existing physic-chemical models of double electrical layer. The results obtained show that the tensor of effective complex permittivity of a micro-heterogeneous medium with surface effects has complicate dependences on the component electrical properties, spatial material texture, and the inclusion shape (ellipsoid aspect ratio) and size. The dispersion of dielectric permittivity corresponds to the frequency dependence for individual inclusion of given size, and does not depend on the inclusion concentration.