Graphene-supported tunable extraordinary transmission

Polarization-sensitive tunable extraordinary terahertz transmission based on a hybrid metal-vanadium dioxide metasurface

Thermally tunable extraordinary terahertz transmission in a hybrid metal-vanadium dioxide (VO₂) metasurface is numerically demonstrated. The metasurface consists of a metal sheet perforated by square loops, while the loops are connected with strips of VO₂. The frequency and amplitude of the transmission resonance are modulated by controlling the conductivity of VO₂. For a y-polarized incident field, the resonance transmission peak redshifts from 0.88 to 0.81 THz upon insulator-to-metallic phase transition of VO₂. For an x-polarized incident field, the transmission resonance at 0.81 THz is observed in the insulator phase. However, in the metallic phase of VO₂, the electromagnetic field is effectively reflected in the 0.5-1.1 THz range with a transmission level lower than 0.14. The proposed metasurface can be utilized as a terahertz modulator, reconfigurable filter, or switch.

High-efficiency transmissive invisibility cloaking based on all-dielectric multilayer frame structure metasurfaces

Metasurfaces provide a completely new path to realize the cloaking effect due to their excellent electromagnetic wavefront manipulation. However, most previous metasurfaces realized cloaking by using phase compensation, which is limited by the reflection phase formula and can be used only for reflection mode. We use the generalized Snell's law to propose a free-space transmission stealth device, consisting of multilayer all-dielectric metasurfaces. We utilize three phase gradient all-dielectric silicon metasurfaces that, respectively, play the role of beam splitting, steering, and collection to guide incident waves around the object, thereby forming an ideal stealth area in free space. All-dielectric metasurfaces can greatly reduce transmission loss and enhance efficiency to a large extent. The advantage of choosing an all-dielectric material is that it is easy to process and more suitable in practice. Simulation results of the near field and far field prove that this cloak has a cloaking effect at 1 THz. Our work opens up a new path for transmissive stealth.

Z-scheme TiO2@Ti3C2/Cd0.5Zn0.5S nanocomposites with efficient photocatalytic performance via one-step hydrothermal route

Photocatalytic degradation of pollutants has been proved to be an effective strategy for wastewater treatment. Herein, TiO₂ nanoparticles were synthesized on a Ti₃C₂ matrix by in situ growth, forming Z-scheme TiO₂@Ti₃C₂/Cd_0.5Zn_0.5S (TO/CZS) multilevel structured nanocomposites via one-step hydrothermal route. The effects of hydrothermal temperature and Cd_0.5Zn_0.5S content on microstructure and properties of composites were assessed. TO/CZS nanocomposites were probed into phase composition, morphological and optical properties with x-ray diffractometer, infrared radiation, scanning electron microscope and UV-vis reflective spectra. Following the hydrothermal reaction at 160 °C for 12 h, TiO₂ nanoparticles of 30 nm in diameter were generated in situ on Ti₃C₂ lamina and Cd_0.5Zn_0.5S particles were evenly distributed on the Ti₃C₂ matrix. The photocatalytic activity of TO/CZS composites were evaluated, which found that degradation rate constant (k = 0.028 min^-1) of TO/CZS-40 on Rhodamine B was 5.19 times that of pure TiO₂ and 4.48 times that of Cd_0.5Zn_0.5S. Through anchoring Ti₃C₂ as an electron transition mediator and combination with TiO₂ and Cd_0.5Zn_0.5S, the new Z-scheme between TiO₂ oxidized by Ti₃C₂ and Cd_0.5Zn_0.5S establishes a multilevel structure of separating electron-hole pairs. This work demonstrates a valid way to control electrons and hole transfer directions efficiently through designing multilevel semiconductor structural designs.

Design of two invisibility cloaks using transmissive and reflective metamaterial-based multilayer frame microstructures

Ultrathin metamaterials provide new possibilities for the realization of cloaking devices because of their ability to control electromagnetic waves. However, applications of metamaterials in cloaking devices have been limited primarily to reflection-type carpet cloaks. Hence, a transmissive free-space cloak was developed using a multilayer frame structure, wherein highly transparent metamaterials were used to guide incident waves into propagating around an object. The cloaking effect was quantitatively verified using near-field and far-field distributions. Metamaterials allow for the cloaking shells of transmissive cloaks to be developed without spatially varying extreme parameters. Moreover, a transmissive invisible cloak with metamaterial-based mirrors was designed. The design principle of this cloak with a frame structure consists of four metamaterial-based mirrors and two metal mirrors. After covered with the designed metamaterials-based mirrors cloak, the outgoing electromagnetic wave is restored greatly as if the wave passes directly through the obstacle without distortion. This cloak used the metamaterials mirrors to adjust the reflected angle, so that the outgoing electromagnetic wave does not change direction, thereby achieving the cloaking effect.

Manipulation of the arbitrary scattering angle based on all-dielectric transmissive Pancharatnam Berry phase coding metasurfaces in the visible range

In order to improve the transmitted efficiency of the metasurface in the visible range, an all-dielectric Pancharatnam-Berry phase unit structure was proposed. Using these Pancharatnam-Berry phase element particles with different rotation angles, all-dielectric encoding metasurfaces can be constructed. The encoding metasurface connects the physical coding particles with digital coding in digital signal processing. The manipulation of the continuous transmission angle requires the continuous change of the encoding metasurface period. Since the size of encoding particles on the coded metasurfaces cannot be designed to be infinitesimally small, it is impossible to obtain the continuously changing period of the coded metasurfaces. To manipulate effectively and freely the angle of scattering in the visible range, Fourier convolution principle in digital signal processing was introduced on all-dielectric encoding metasurfaces with Pancharatnam-Berry phase meta-atoms. The addition and subtraction operations on two initial encoding sequences can be implemented to obtain a new encoding sequence. The manipulation of the arbitrary scattering pattern after Fourier convolution operations on different encoding sequences can be realized, especially for larger abnormal deflection angles. The checkerboard encoding metasurface was also designed to further prove the applicability of the Fourier convolution principle. Moreover, by using the proposed all-dielectric highly efficient Pancharatnam-Berry phase encoding meta-atoms, these coded particles with different rotation angles can be precisely arranged to build the generators of the orbital angular momentum beam with different topological charges.

Biofabrication of gold nanoparticles mediated by the endophytic Cladosporium species: Photodegradation, in vitro anticancer activity and in vivo antitumor studies

Green fabrication of nanoparticles (NPs) using biological sources is the fast-growing trend replacing chemical synthesis via toxic materials. Considering the importance and feasibility of green fabricated NPs, the present research focuses on the synthesis of gold nanoparticles (AuNPs) using the aqueous extract of the endophytic Cladosporium sp. (MycoAuNPs) isolated from Commiphora wightii. The synthesized MycoAuNPs are characterized using UV-Vis spectroscopic, FTIR, X-ray diffraction (XRD) analysis, and transmission electron microscopy (TEM). The synthesized NPs showed a sharp absorption peak at 524 nm, with an average size between 5 and 10 nm in a spherical shape. XRD revealed the crystalline nature, and EDX profiling confirmed the presence of gold (Au) and oxygen (O) atoms. The biological potential of MycoAuNPs were tested under both in vitro and in vivo conditions. MycoAuNPs showed anti-cancer activity in breast cancer cell line MCF-7 (IC₅₀ 38.23 µg/mL) through the induction of apoptosis. Further, MycoAuNPs showed potential against growth of tumor in tumor-bearing mice models. MycoAuNPs significantly reduced the body weight, ascites volume, and increased the lifespan of EAC bearing mice. It induced apoptosis of the EAC cells, which was confirmed by DNA fragmentation and Giemsa staining. Also, they did not develop any secondary complications or side effects in normal mice. The photocatalytic activity of MycoAuNPs tested against Rhodamine B and Methylene Blue dyes showed potential dye degradation in the presence of sunlight. Thus, the present study gives a clear idea of the multifaceted therapeutic and catalytic applications of the biosynthesized MycoAuNPs.

Efficient Optical Reflection Modulation by Coupling Interband Transition of Graphene to Magnetic Resonance in Metamaterials

Designing powerful electromagnetic wave modulators is required for the advancement of optical communication technology. In this work, we study how to efficiently modulate the amplitude of electromagnetic waves in near-infrared region, by the interactions between the interband transition of graphene and the magnetic dipole resonance in metamaterials. The reflection spectra of metamaterials could be significantly reduced in the wavelength range below the interband transition, because the enhanced electromagnetic fields from the magnetic dipole resonance greatly increase the light absorption in graphene. The maximum modulation depth of reflection spectra can reach to about 40% near the resonance wavelength of magnetic dipole, for the interband transition to approach the magnetic dipole resonance, when an external voltage is applied to change the Fermi energy of graphene.

Strong Coupling between a Quasi-single Molecule and a Plasmonic Cavity in the Trapping System

We theoretically investigate the strong coupling phenomenon between a quasi-single molecule and a plasmonic cavity based on the blue-detuned trapping system. The trapping system is made up of a metallic nanohole array. A finite-difference time-domain method is employed to simulate the system, and the molecule is treated as a dipole in simulations. By calculating the electromagnetic field distributions, we obtain the best position for trapping a molecule, and we get the strong coupling phenomenon that there are two splitting peaks in the transmission spectrum when the molecule is trapped in the structure, while only one peak is observed in the one without the molecule. We also find that only when the molecule polarization parallels to the incident light wave vector can we observe a strong coupling phenomenon.

Investigation of the tunable properties of graphene complementary terahertz metamaterials

Based on the graphene–SiO₂–Si structure, the tunable resonant properties of the complementary graphene metamaterials (MMs) have been investigated in the terahertz regime.