Multiple Dielectric Resonances Research Articles

Investigation of dual-band perfect absorption and their hybridization on multilayer tungsten disulfide (WS2) gratings

We investigate the dual-band perfect absorption and their hybridization on multilayer tungsten disulfide (WS2) gratings with metallic substrates by the finite-difference time-domain method and the coupled-mode theory. Numerical results suggest that, under the illumination of the transverse magnetic polarized plane wave, the special multilayer WS2 grating with high refractive index not only allows the circulating-current-drove magnetic resonance but also provides additional wavevectors to excite the plasmonic resonance on the substrate surface simultaneously. Consequently, the dual-band perfect absorption is obtained in the single-port system by two independent critical coupling. The effect of small changes in the grating period, width, and height on spectral positions of absorption peaks is presented. The inherent multiple dielectric resonances on the WS2 grating under the illumination of the transverse electric polarized plane wave are also demonstrated. Intriguingly, the simultaneous existence of angle-independent magnetic resonances and angle-dependent plasmonic resonances gives rise to the obvious hybridization between the two types of resonances under the oblique incidence. Numerical results are in excellent agreement with theoretical calculations. The structure under study undoubtedly opens perspectives for enhancing light–matter interactions in two-dimensional materials.

Engineering multimodal dielectric resonance of TiO2 based nanostructures for high-performance refractive index sensing applications

Optical metasurface based refractive index (RI) sensors find applications in chemical, environmental, biomedical, and food processing industries. The existing RI sensors based on metals suffer from the plasmonic loss in the optical regime; in contrast, those based on Fano-type resonances generated by dielectric materials are either polarization-sensitive or are based on complex geometrical structures prone to fabrication imperfections that can lead to severe performance degradation. Here, we demonstrate that careful engineering of resonance modes in dielectric metasurfaces based on simple symmetric meta-atoms can overcome these limitations. More specifically, we have designed low-loss high-performance RI sensors using all-dielectric metasurfaces composed of TiO2 based nanostructures of three different shapes (i.e., cylindrical, square and elliptical) operating at near-infrared (NIR) wavelengths, which are robust against the perturbations of geometric parameters. In terms of physics, this work reports sensor structures achieving sharp resonant dips of high Q-factor in the transmission spectra corresponding to multiple dielectric resonance modes (i.e., electric quadrupole, magnetic dipole, and electric dipole) with superior performance as compared to the state-of-the-art. Four absolute liquids (water, ethanol, pentanol, and carbon tetrachloride) with a refractive index ranging from 1.333 to 1.453 are used to numerically validate the performance, and a maximum sensitivity of 798 nm/RIU with FOM up to 732 has been achieved.

Multiple dielectric resonance behaviors and microwave attenuation in vanadium nitride/vanadium sesquioxide nanowires

Vanadium nitride/vanadium sesquioxide nanowires (VN/V2O3 NWs) with multiple dielectric resonance behaviors were prepared by a simple method of partial nitridation. By many approach utilization, it was discovered that the one-dimensional (1D) structure of the as-prepared material was efficiently kept after partial nitridation. Nanoparticles-stacked VN/V2O3 NWs caused multiple dielectric resonances and then enhanced microwave attenuation. The as-prepared material exhibited good microwave absorption performances in X-band (8.2–12.4 GHz): a minimum reflection loss (RL) of −41.0 dB with an absorption bandwidth of 3.0 GHz (RL < −10 dB) at a thickness of 1.8 mm. Microwave energy could be effectively attenuated by multiple dielectric resonances and enhanced dielectric loss resulted from the special structure. Therefore, the design strategy of partial nitridation in this work can open a road for designing others 1D microwave absorbers.

A scalable chemical vapor deposition synthesis of high purity hollow carbon onions

Carbon onions have shown potential applications in many fields due to their low density, tunable conductivity, excellent thermal and chemical stability. In this study, we report an efficient method for synthesis of gram-scale hollow carbon onions (HCNOs). A chemical vapor deposition (CVD) process was carried out at 700 °C with magnesium oxide supported cobalt as catalyst. Abundant HCNOs were obtained by leaching the CVD product in hydrochloric acid when the precursor weight ratio of cobalt and magnesium oxide is 5%. Scanning electron microscopy and transmission electron microscopy images indicate the sample is composed of hollow polyhedral particles with diameter of 10–50 nm. The thermogravimetric analysis indicates the purity of HCNOs is about 99%. X-ray diffraction and Raman spectra demonstrates a moderate graphitization of HCNOs in which graphite carbon and defective carbon both present. The graphite carbon can provide good conduction that is beneficial to introduce the microwave, while the defects can provide abundant polarization center to stimulate the formation of multiple dielectric resonances. The calculated reflection loss curve of HCNOs with a thin thickness of 2 mm exhibit wide absorption bandwidth at high frequency (13.5–16.9 GHz), indicating an excellent microwave absorption performance at high frequency.

The arc-discharged Ni-cored carbon onions with enhanced microwave absorption performances

Carbon-based microwave absorbers are important for the rapid development of electronic devices. Herein Ni-cored carbon onions with wide particle size distribution were prepared via arc discharge method, and their structures were characterized by electron microscope, X-ray diffraction, Raman spectroscopy. The three-dimension porous structure, thick carbon shell and large number of defects endows Ni-cored carbon onions with various polarization centers that can stimulate multiple dielectric resonances, leading to wide response frequency bandwidth and multiple strong microwave absorption features. It was evidenced that the bandwidths over −10 dB were from 3.4 to 18.0 GHz when the thickness of samples ranged from 1.5 to 5.0 mm.

SERS-active dielectric metamaterials based on periodic nanostructures.

New dielectric SERS metamaterial is investigated. The material consists of periodic dielectric bars deposited on the metal substrate. Computer simulations as well as real experiment reveal extraordinary optical reflectance in the proposed metamaterial due to the excitation of the multiple dielectric resonances. We demonstrate the enhancement of the Raman signal from the complex of 5,5'-dithio-bis-[2-nitrobenzoic acid] molecules and gold nanoparticle (DTNB-Au-NP), which is immobilized on the surface of the barshaped dielectric metamaterial.

The hierarchical three-dimensional cobalt superstructure: Controllable synthesis, electromagnetic properties and microwave absorption

A close-packed hexagonal (HCP)-cobalt superstructure was synthesized on a large scale through a simple, yet low-cost liquid reduction method. The cobalt superstructure was assembled by nanoflakes with strong shape anisotropy. The permittivity (εr=ε′-jε″) and permeability (μr=μ′-jμ″) of cobalt superstructure were also studied as a function of frequency in microwave range of 1–18GHz. It is demonstrated that permittivity displays remarkable multiple dielectric resonance peaks. Multiple magnetic resonances were also exhibited for permeability, which were discussed based on the LLG equation and exchange resonance mode. Multiple dielectric and magnetic resonances were beneficial to widen microwave absorption bandwidth. The calculated reflection loss (RL) indicated that the cobalt superstructure had potential application as a promising candidate for microwave absorption. The reflection loss was attributed to two main reasons, one is the destructive interference, which was related to the thickness of the absorbent layer, and the other one was multiple microwave reflection due to the structure assembled by nanoflakes.

Synthesis, magnetic resonance and microwave absorption properties of cobalt nanospheres

By using a simple and low-cost liquid reduction method, we have synthesized cobalt nanospheres on a large scale. The materials were characterized, and the result showed that as-prepared products were cobalt nanospheres, assembled by nanosheets in parallel, with a size of around 100 nm. The electromagnetic behaviors of the cobalt nanospheres, including permittivity () and permeability (), were also investigated as a function of frequency in the microwave frequency range of 2–18 GHz. The permittivity presented multiple dielectric resonance peaks whilst the permeability displayed dual obvious magnetic resonance peaks, manifestly different from other cobalt particles in comparison. The calculated reflection loss (RL) indicated there were two strong microwave absorption peaks over the microwave frequency range of 2–18 GHz, which was in accord with the magnetic resonance peaks. The result revealed that the magnetic loss contributed even more than dielectric loss to the microwave absorption for the cobalt nanospheres.

Effect of the TiO2 amounts on microwave absorption properties of Ni/TiO2 heterostructure composites

Hybrid core/shell Ni/TiO2 composites were prepared with different contents of tetrabutyl orthotitanate (TBOT). The microwave absorption properties of the Ni/TiO2 composites have been studied in the range of 1–18GHz. The amount of TiO2 is found to have a great impact on the microwave absorption of this metal–semiconductor composite. The microwave absorption properties of Ni/TiO2 heterostructure prepared at 2mL TBOT were highly enhanced compared with other two samples. The excellent microwave absorption properties are due to the proper complementarities between magnetic loss and dielectric loss, geometrical effect, the natural resonance and multipolarization. The multiple dielectric resonances are attributed to interfacial polarization and the magnetic resonances are ascribed to natural resonance.

Submillimeter-wave phonon modes in DNA macromolecules.

A detailed investigation of phonon modes in DNA macromolecules is presented. This work presents experimental evidence to confirm the presence of multiple dielectric resonances in the submillimeter-wave spectra (i.e., approximately 0.01-10 THz) obtained from DNA samples. These long-wave (i.e., approximately 1-30 cm(-1)) absorption features are shown to be intrinsic properties of the particular DNA sequence under study. Most importantly, a direct comparison of spectra between different DNA samples reveals a large number of modes and a reasonable level of sequence-specific uniqueness. This work establishes the initial foundation for the future use of submillimeter-wave spectroscopy in the identification and characterization of DNA macromolecules.

Submillimeter-wave Fourier transform spectroscopy of biological macromolecules

In this article we report experimental results on Fourier-transform infrared spectroscopy of deoxyribonucleic acid (DNA) macromolecules and related biological materials in the submillimeter range (i.e., ∼10–500 cm−1). Film samples made from commercial DNA fibers, polyadenylic acid potassium salt, and cellular agents such as the spore form of Bacillus subtillis have been prepared and measured. A broad series of measurements carried out in the low frequency region (10–50 cm−1) with a higher resolution of 0.2 cm−1 revealed fine features—multiple dielectric resonances in the submillimeter-wave spectra obtained from DNA samples. These long-wave absorption features are shown to be intrinsic properties of biological materials determined by phonon modes. The emphasis is on reproducibility of experimental spectra and on receiving reliable results. The effects of differences in sample preparation, including sample geometry, orientation, and aging are studied and separated from the phonon effects that determine the fine structure of transmission spectra. A direct comparison of spectra between different DNA samples reveals a large number of modes and a reasonable level of sequence-specific uniqueness. A theoretical study of two double helical DNA fragments has applied a normal mode analysis to predict spectra in the far infrared. Most of the modes determined by long-distance interactions are at frequencies below 220 cm−1, with the density higher than one mode per cm−1, which is approximately what was observed experimentally.