High-efficiency reflective terahertz cross-polarization converter with broadband and wide-angle response.

In this paper, a broadband terahertz metasurface dedicated to cross-polarization conversion was designed, fabricated, and assessed. The metasurface, comprising two nested double-split rings, features an inherent insensitivity to the angle of incidence. Simulations reveal that the converter achieves a >99% polarization conversion efficiency across the 90-140 GHz range. Moreover, it maintains a >90% polarization conversion ratio (PCR), even at a 50° incidence angle. The sample, featuring 50×70 arrays, was fabricated, and the relevant experimental results align closely with the simulated outcomes. The metasurface characteristics can markedly enhance the performance of cross-polarization converters operating in the terahertz range.

Manipulation of sub-terahertz waves using digital coding metasurfaces based on liquid crystals.

This paper presents a novel sub-terahertz liquid crystal (LC) phase shifter based on digital coding metasurfaces. The proposed structure consists of metal gratings and resonant structures. They are both immersed in LC. The metal gratings function as reflective surfaces for electromagnetic waves and electrodes for controlling the LC layer. The proposed structure changes the state of the phase shifter by switching the voltage on every grating. It allows the deflection of LC molecules within a subregion of the metasurface structure. Four switchable coding states of the phase shifter are obtained experimentally. The phase of the reflected wave varies by 0°, 102°, 166°, and 233° at 120 GHz. Due to the presence of the transverse control electric field, modulation speed is approximately doubled compared to the free relaxation state. This work provides a novel idea for wavefront modulation of phase.

Electrically controllable broadband reflective linear cross-polarization conversion based on liquid crystals.

This paper presents an electrically controllable reflective broadband linear polarization (LP) converter based on liquid crystals (LCs) for cross-polarization conversion (CPC) in the terahertz frequency range. The proposed structure achieves a high polarization conversion ratio (PCR) exceeding 0.9 within the frequency range of 236.8 - 269.6 GHz. A vital feature of this design is the dynamic control of polarization conversion by re-orienting the nematic liquid crystal molecules through voltage bias switching between 'on' and 'off' states, allowing for precise manipulation of cross-polarized and co-polarized reflected waves. Experimental results validate the simulation outcomes, demonstrating excellent agreement. In contrast to conventional reflective polarization converters with fixed frequency responses, the proposed electrically controllable polarization conversion offers significant potential in imaging and optical communications.

Wideband linear cross-polarization conversion with 3D metamaterial configuration.

In this Letter, a broadband and wide-angle linear polarization (LP) converter based on a 3D resonator for cross-polarization conversion (CPC) is presented. The designed structure performs a CPC with a polarization conversion ratio (PCR) of more than 90% in the frequency range 16.32 to 34.12 GHz, corresponding to a relative frequency bandwidth of 70.6%. Moreover, the presented structure possesses broad angle stability and miniaturized configuration. The efficiency of CPC remains over 90% in the operational frequency band with the incident angles up to 40°, and the cell size is 0.18λ for the lowest frequency of the CPC operational band. The proposed 3D structure is fabricated using the multi-material hybrid microdroplet jetting modeling (MHMJM) technique, and the experiments agree closely with the simulated results. Compared with traditional polarization converters based on a planar resonant structure, the proposed design shows excellent bandwidth, wide-angle performance, and miniaturization advantages.

Palladium-Catalyzed Reductive Double Carbonylation of Nitroarenes with Aryl Halides Using Mo(CO)6 as a Reductant and Carbonyl Source.

A new palladium-catalyzed reductive double carbonylation of nitroarenes with aryl halides for the synthesis of benzoxazin-4-ones has been reported. The key to success was the use of Mo(CO)6 as a reductant and bench-stable solid carbonyl sources. Various aryl iodides, bromides, and trifluoromethanesulfonates are suitable reaction partners and produce corresponding benzoxazin-4-one derivatives in moderate to good yields. Preliminary mechanistic studies indicate that nitrosoarene was first generated as the key intermediate through nitro reduction. Remarkably, this method avoids the use of toxic CO gas and is further applied to the late-stage modification of estrone.

Transition-Metal-Catalyzed Carbonylative Multifunctionalization of Alkynes.

Currently, the construction of new carbon-carbon bonds and value-added structures in an atom- and step economical manner has become a continuous pursuit in the synthetic chemistry community. Since the first transition-metal-catalyzed hydroformylation of ethylene was reported by Otto Roelen in the 1930s, impressive progress has been achieved in the carbonylative functionalization of unsaturated C-C bonds. In contrast to alkenes, the carbonylative functionalization of alkynes offers tremendous potential for the construction of multisubstituted carbonyl-containing derivatives because of their two independently addressable π-systems. This review provides a timely and necessary investigation of transition-metal-catalyzed carbonylative mutifunctionalization of alkynes with the exclusion of carbonylative hydrofunctionalizations. Different transition metals including palladium, rhodium, iridium, ruthenium, iron, copper, etc. were applied to the development of novel carbonylative transformation. Various C-C, C-N, C-O, C-S, C-B, C-Si, and carbon-halogen bonds were formed efficiently and give the corresponding tri- or tetrasubstituted α,ß-unsaturated ketones, diesters, and heterocycles.

Optimized sinusoidal patterns for high-performance computational ghost imaging.

Computational ghost imaging (CGI) can reconstruct scene images by two-order correlation between sampling patterns and detected intensities from a bucket detector. By increasing the sampling rates (SRs), imaging quality of CGI can be improved, but it will result in an increasing imaging time. Herein, in order to achieve high-quality CGI under an insufficient SR, we propose two types of novel sampling methods for CGI, to the best of our knowledge, cyclic sinusoidal-pattern-based CGI (CSP-CGI) and half-cyclic sinusoidal-pattern-based CGI (HCSP-CGI), in which CSP-CGI is realized by optimizing the ordered sinusoidal patterns through "cyclic sampling patterns," and HCSP-CGI just uses half of the sinusoidal pattern types of CSP-CGI. Target information mainly exists in the low-frequency region, and high-quality target scenes can be recovered even at an extreme SR of 5%. The proposed methods can significantly reduce the sampling number and real-time ghost imaging possible. The experiments demonstrate the superiority of our method over state-of-the-art methods both qualitatively and quantitatively.

High-Efficiency Multi-Channel Orbital Angular Momentum Multiplexing Enabled by the Angle-Dispersive Metasurface.

Orbital angular momentum (OAM) multiplexing of electromagnetic (EM) waves is of great significance for high-speed wireless communication and remote sensing. To achieve high-efficiency OAM multiplexing for multi-channel incident EM waves, this paper presents a novel angle-dispersive meta-atom structure, which can introduce the required anti-symmetric phase dispersion as well as high transmission efficiency for OAM multiplexing. These meta-atoms are then arranged delicately to form an angle-dispersive metasurface working at the X band, which enables three-channel OAM multiplexing by converting highly directional transverse-magnetic (TM) waves incident from 0 and ±45° to coaxial OAM beams with l = 0 and ±2 modes, respectively. The simulation and experimental results reveal that the proposed metasurface can convert a higher proportion of energy to the required OAM modes compared to the conventional OAM multiplexing metasurfaces, which can significantly improve the coaxial transmission efficiency of multi-channel OAM multiplexing.

Liquid crystal-based wide-angle metasurface absorber with large frequency tunability and low voltage.

A tunable metasurface absorber (MA) based on polymer network liquid crystal is introduced in this paper. Despite the well-designed unit cell patterns, the proposed MA can achieve both large frequency tunability and wide-angle stability. Compared with traditional liquid crystal-based metasurfaces, the measured results suggest that the recovery time of the proposed structure was reduced by half. By applying an external voltage on the top electrode of the liquid crystal layer from 0 to a saturation voltage of 10 V, the absorption peak of the MA can be tuned from 112.7 GHz to 102.2 GHz, with a maximum frequency tunability of 9.3%, which is significantly higher than other proposed liquid crystal-based metasurfaces. Moreover, the proposed tunable absorber can maintain absorption greater than 90% with incident angles reaching up to 60° for both transverse electric and transverse magnetic polarizations. This design provides an efficient way for developing low-power consumption terahertz devices with large frequency tunability and wide-angle stability.

Active continuous control of terahertz wave based on a reflectarray element-liquid crystal-grating electrode hybrid structure.

In this work, a new and efficient terahertz reflective phase shifter is proposed. The phase shifter is composed of a metal-dielectric-metal structure with a double dipole patch array, as well as copper grating electrodes immersed within the nematic liquid crystal. More specifically, the employed copper grating electrodes consist of two sets of cross-distributed comb grids, whereas at each set of comb grids can be applied an external bias voltage separately. On top of that, the electric field in the liquid crystal (LC) layer can be continuously changed by enforcing an innovative technique. Consequently, the orientation of the LC molecules was fully controlled by the applied electric field, since the dielectric constant of the LC is controlled by the biased voltage. The phase of the reflective electromagnetic wave can be continuously manipulated. Under this direction, the experimental results show that the phase shift exceeds the value of 180° in the range of 102.5 GHz-104.3 GHz, where the maximum phase shift is 249° at 103 GHz. The proposed work provides a new regulation concept for the implementation of LC-based terahertz devices and the respective applications in the terahertz reconfigurable antennas field.

Rapid terahertz wave manipulation in a liquid-crystal-integrated metasurface structure.

A terahertz phase shifter based on liquid-crystal-integrated metasurface is proposed, which contains a three-slotted array structure and comb grating. The orientation of the liquid crystal molecules can be completely controlled by the direction of the electric field. From the acquired experimental results, it was demonstrated that the phase shift exceeds 300° in the range of 378.6 - 390.8 GHz, whereas the maximum phase shift reaches 374.1° at 383.1 GHz. The molecular reorientation transient process induced by the external electric field in the liquid crystal was measured and analyzed. Based on the molecular reorientation mechanism, which can be divided into three processes, a rapid modulation mechanism was demonstrated. From the performance of the proposed device, an actively controllable phase delay and reflectance with a cycle switching time of approximately 0.3 s was achieved, which is remarkably faster than the usual cycle time that exceeds 8 s. Our work provides useful ideas for improving the response speed of LC-based terahertz devices, which is considered of great significance for several applications, in terms of terahertz reconfigurable devices.

Computational design of a new layered superconductor LaOTlF2.

A new layered compound LaOTlF2 is designed and investigated using first-principles calculations in this work. The parent compound is an insulator with an indirect band gap of 3.88 eV. Electron-doping of the parent compound makes the material metallic. In the meantime, several lattice vibrational modes couple strongly to the conduction band, leading to a large electron-phonon coupling constant and conventional superconductivity. The highest superconducting transition temperature Tc is predicted to be approximately 8.6 K with λ about 1.25 in the optimally doped LaO0.95F0.05TlF2, where λ is calculated using the Wannier interpolation technique.

Ginsenoside RG1 augments doxorubicin-induced apoptotic cell death in MDA-MB-231 breast cancer cell lines.

This study determined the chemosensitizing potential of ginsenoside Rg1 in triple-negative MDA-MB-231 breast cancer cell lines. Ginsenoside Rg1 (10 µM) treated breast cancer cells were exposed to 8 nM of doxorubicin, and the chemosensitizing potential was measured by cell-based assays. Ginsenoside Rg1 (10 µM) treatment lowered the doxorubicin IC50 value to 0.01 nM. Furthermore, the ginsenoside pretreatment augments doxorubicin-mediated reactive oxygen species (ROS) generation and subsequent alterations of mitochondrial membrane potential in MDA-MB-231 cell lines. The alkaline comet assay results illustrated an increased % tail DNA during ginsenoside Rg1 plus doxorubicin treatment than doxorubicin alone treatment. In addition, the number of apoptotic cells was also increased in ginsenoside Rg1 plus doxorubicin-treated cells. Furthermore, the polymerase chain reaction array results illustrate activation of mitogen-activated protein kinase (MAPK) gene expression (AKT, ERK, and MAPK) during doxorubicin alone treatment and it has been attenuated by ginsenoside Rg1 pretreatment. Moreover, ginsenoside Rg1 treatment before doxorubicin activates the DNA damage response elements (ATM, H2AX, RAD51, and XRCC1) and subsequent apoptosis-related gene expression (p21, TP53. APAF1, Bax, CASP3, and CASP9) patterns in MDA-MB-231 cell lines. The ginsenoside Rg1 plus doxorubicin combination shows less cytotoxicity and ROS generation in MDA10A normal breast cancer cell lines. Therefore, the present results support the chemosensitizing property of ginsenoside Rg1 in triple-negative breast cancer cell lines.

Highly efficient and tunable terahertz polarization converter based on double subwavelength metallic gratings infiltrated with liquid crystal.

In this work, a tunable cross-polarized transmission structure at the terahertz frequency was demonstrated, and the polarization state during modulation was investigated. The proposed structure can significantly enhance the polarization conversion performance of nematic liquid crystals by leveraging the formation of a Fabry-Perot-like resonant cavity that consists of two metal gratings. As a result, the incident waves are continuously reflected in the liquid crystal layer to complete the accumulation of polarization angle changes. From the experimental results acquired, it was concluded that the insertion loss of the cross-polarization transmission was less than 3 dB and the extinction ratio was larger than 28 dB in the frequency range of 388-426 GHz. Our work provides useful insights for improving the efficiency of cross-polarization conversion by enhancing the resonance process in a Fabry-Perot-like resonant cavity and, thus, significantly extending the equivalent optical path.

Electrically active control of terahertz waves in a hybrid metasurface-grating structure with a liquid crystal.

A reflective terahertz phase shifter for wide-range dynamic and continuous phase modulation is proposed. By injecting a tunable liquid crystal between the slotted metasurface and the grating microstructure, the phases of reflected waves can be modulated with different electrically driven methods. Numerical simulations show that the proposed terahertz phase shifter has a phase difference of more than 360° between unbiased and biased states. Furthermore, an array of 35×35 patch elements was designed and fabricated. The performance of the phase shifter provides more than 360° between 379.6 and 391.8 GHz, where the maximum phase shift reaches 422.4° at 385.9 GHz. Moreover, the fully electrically controlled phase modulation of more than 180° is achieved between 382.0 and 394.1 GHz, with a maximum phase modulation of 248.4° at 383.3 GHz. This work may provide a reflective terahertz phase modulator for beam steering.

TM-polarized angle-dispersive metasurface for axisymmetric extension of beam steering angles.

Axisymmetric extension of beam steering angles by metasurfaces is of great interest due to its potential application in extending the angular scan range of existing phased arrays. This angle-multiplexed manipulation functionality requires anti-symmetrically angle-dispersive phase gradient, as well as anti-symmetric angular phase dispersion over continuous incident angles, which is difficult to be implemented by existing metasurfaces. In this work, a series of meta-atoms with asymmetric structures are developed to achieve the required phase response. Based on the asymmetric meta-atoms, an angle-dispersive metasurface for axisymmetric beam steering of transmitted transverse-magnetic (TM) wave is designed, fabricated and tested, whose simulation and experimental results demonstrate the axisymmetric extension capability of beam steering angles from -53° ≤ θi ≤ 53° to almost -90° ≤ θt ≤ 90°.

Graphene-based wavelength demultiplexing structure.

A wavelength demultiplexing (WDM) structure based on graphene nanoribbon resonators is proposed and simulated using the finite-difference time-domain (FDTD) method. Based on a simple structure, the demultiplexing wavelength and transmission characteristics of the WDM can be tuned by adjusting the length of the resonator, the nanoribbon width, or the chemical potential of graphene within a relative broadband frequency range. Moreover, the mechanism of the proposed WDM structure is analyzed in detail using the theory of Fabry-Perot (F-P) resonance and temporal coupled-mode theory. The proposed structure has promising potential in the field of ultracompact WDM systems in highly integrated optical circuits.

Intercalating Anions between Terminated Anion Layers: Unusual Ionic S-Se Bonds and Hole-Doping Induced Superconductivity in S0.24(NH3)0.26Fe2Se2.

The pairing of ions of opposite charge is a central principle of chemistry. Even though the ability to intercalate anions is desirable for many applications, it remains a key challenge for numerous host materials with their outmost layers beingn anions. In this work, we introduce a hydrothermal ion-exchange synthesis to intercalate oxidative S and Se anions between the Se layers of FeSe, which leads to single crystals of novel compounds (Se/S)x(NH3)yFe2Se2. In particular, the unusual anion-anion bonding between the intercalated S (or Se) and Se layers exhibits strong ionic characteristics. The charge transfer through the Se layer to S (or Se) intercalants is further confirmed by the elevated oxidation state of Fe ions and the dominant hole carriers in the intercalated compounds. By intercalating S, for the first time superconductivity emerged in hole-doped iron chalcogenides. The generality of this chemical approach was further demonstrated with layered FeS and NiSe. Our findings thus open an avenue to exploring diverse aspects of anionic intercalation in similar materials.

Electrically tunable liquid crystal terahertz device based on double-layer plasmonic metamaterial.

In this paper, a nematic liquid crystal (NLC)-based tunable terahertz (THz) plasmonic metamaterials (MMs) with large modulation depth (MD) and low insertion loss (IL) is designed and experimentally verified at THz frequencies. The proposed structure includes two-layered MM that is immersed in LC. The metal MM is used directly as electrode. The tunable device with a 46×46 array of sub-wavelength circular air loops was fabricated on a quartz glass substrate, with 2×2 cm2 area and 220 µm thickness. The obtained results show that the amplitude MD and IL for normally incident electromagnetic (EM) waves are about 96% and 1.19 dB at 421.2 GHz, respectively, when the bias voltage applied to the NLC layer varies from 0 to 16 V. Meanwhile, the transmission peak frequency gradually decreases from 421.2 to 381.8 GHz, and the frequency tunability (FT) of the proposed structure is greater than 9.35%. This study provides a potential solution for THz modulators, filters, and switches.

Tunable THz generalized Weyl points.

Weyl points, as linearly double degenerated point of band structures, have been extensively researched in electronic and classical wave systems. However, Weyl points' realization is always accompanied with delicate "lattice structures". In this work, frequency-tunable terahertz (THz) generalized Weyl points inside the parameter space have been investigated and displayed by a specially designed photonic crystal with polydimethylsiloxane (PDMS) immersed in 4-cyano'-pentylbipenyl (5CB) liquid crystals (LCs). The reflective phase vortices as a signature of the generalized Weyl points are observed through our numerically simulations. Besides, interface states between photonic crystals and any reflective substrates are fulfilled too. Meanwhile, we could also change the orientation of LC molecule by the external magnetic field so as to tune the frequency of the first two bands' Weyl point from 0.27698THz to 0.30013THz. This band lies in the short-range wireless communication. Thus, our proposal may be beneficial to the investigation and application of Weyl points' properties and strongly localized states.