High-performance circular polarization modulation using a dielectric metasurface.

We demonstrate a chiral metasurface that exhibits a giant chiroptical response as well as functions as an optical diode due to geometrical asymmetry for circularly polarized light (CPL). Engineering the Mie-type multipole radiation using geometrical features led to performance values in terms of near-unity transmission and circular dichroism (CD) efficiency (about 0.96) and an extinction ratio of  ∼3.8×104 for 1550 nm wavelength. A continuous stopband of 1538-1556 nm is achieved for an unchosen component of CPL while keeping the transmission efficiency of the chosen CPL component larger than 0.9. Because of the high extinction ratio and CD efficiency, the proposed metasurface has the potential for chiroptical applications including high-contrast polarization imaging, precise Stokes parameters measurement, optical diodes, and polarization detection for CPL.

A Single-Celled Metasurface for Multipolarization Generation and Wavefront Manipulation.

Due to their unprecedented ability to flexibly manipulate the parameters of light, metasurfaces offer a new approach to integrating multiple functions in a single optical element. In this paper, based on a single-celled metasurface composed of chiral umbrella-shaped metal-insulator-metal (MIM) unit cells, a strategy for simultaneous multiple polarization generation and wavefront shaping is proposed. The unit cells can function as broadband and high-performance polarization-preserving mirrors. In addition, by introducing a chiral-assisted Aharonov-Anandan (AA) geometric phase, the phase profile and phase retardation of two spin-flipped orthogonal circular polarized components can be realized simultaneously and independently with a single-celled metasurface via two irrelevant parameters. Benefiting from this flexible phase manipulation ability, a vectorial hologram generator and metalens array with spatially varying polarizations were demonstrated. This work provides an effective approach to avoid the pixel and efficiency losses caused by the intrinsic symmetry of the PB geometric phase, and it may play an important role in the miniaturization and integration of multipolarization-involved displays, real-time imaging, and spectroscopy systems.

Monolayer MXene Nanoelectromechanical Piezo-Resonators with 0.2 Zeptogram Mass Resolution.

2D materials-based nanoelectromechanical resonant systems with high sensitivity can precisely trace quantities of ultra-small mass molecules and therefore are broadly applied in biological analysis, chemical sensing, and physical detection. However, conventional optical and capacitive transconductance schemes struggle to measure high-order mode resonant effectively, which is the scientific key to further achieving higher accuracy and lower noise. In the present study, the different vibrations of monolayer Ti3 C2 Tx MXene piezo-resonators are investigated, and achieve a high-order f2,3 resonant mode with a ≈234.59 ± 0.05 MHz characteristic peak due to the special piezoelectrical structure of the Ti3 C2 Tx MXene layer. The effective measurements of signals have a low thermomechanical motion spectral density (9.66 ± 0.01  fmHz$\frac{{fm}}{{\sqrt {Hz} }}$ ) and an extensive dynamic range (118.49 ± 0.42 dB) with sub-zeptograms resolution (0.22 ± 0.01 zg) at 300 K temperature and 1 atm. Furthermore, the functional groups of the Ti3 C2 Tx MXene with unique adsorption properties enable a high working range ratio of ≈3100 and excellent repeatability. This Ti3 C2 Tx MXene device demonstrates encouraging performance advancements over other nano-resonators and will lead the related engineering applications including high-sensitivity mass detectors.

Ultra-broadband and high-efficiency planar chiral metamaterial.

To date, the helix-like assemblies are known for delivering the most broadband chiroptic response; however, as their dimensions shrink to the nanoscale, it becomes increasingly difficult to realize three-dimensional (3D) building blocks and accurate alignments. In addition, a continuous optical channel requirement hinders the downsizing for integrated photonics. Here, we introduce an alternative approach based on two assembled layers of dielectric-metal nanowires to demonstrate that chiroptic effects similar to helix-like metamaterials can be realized with an ultracompact planar structure by creating dissymmetry using orientation and making use of interference phenomena. We constructed two polarization filters for the near-(NIR) and the mid-infrared (MIR) spectrums that exhibit a broadband (0.835-2.11 µm and 3.84-10.64 µm) chiroptic response with maximum transmission and circular dichroism (CD) of approximately 0.965 and extinction ratio > 600. The structure is easy to fabricate, independent of alignments, and scalable from the visible to MIR range for applications including imaging, medical diagnostics, polarization conversion, and optical communication.

Spin-decoupled metasurface for broadband and pixel-saving polarization rotation and wavefront control.

In this paper, a strategy to achieve a simultaneous wavefront shaping and polarization rotation, without compromising the number of pixels and energy efficiency as well as having broadband operation range, is proposed. This strategy is based on the application of a spin-decoupled phase metasurface composed by only one set of metal-insulator-metal (MIM) umbrella-shaped chiral unit cells. Quasi-non-dispersive and spin-decoupled phase shift can be achieved simply by changing single structural parameter of the structure. By further merging the Pancharatnam-Berry (PB) geometric phase, conversion of an incident LP light beam into right- and left-handed circularly polarized reflected beams with similar amplitudes, desired phase profiles and controlled phase retardation on a nanoscale is enabled with high efficiency. Based on the proposed strategy, a polarization-insensitive hologram generator with control optical activity, and a multiple ring vortex beam generator are realized. The results obtained in this work provide a simple and pixel-saving approach to the design of integratable and multitasking devices combining polarization manipulation and wavefront shaping functions, such as vectorial holographic generators, multifocal metalenses, and multichannel vector beam generators.

Design of Multifunctional Janus Metasurface Based on Subwavelength Grating.

In this paper, a Janus metasurface is designed by breaking the structural symmetry based on the polarization selection property of subwavelength grating. The structure comprises three layers: a top layer having a metallic nanostructure, a dielectric spacer, and a bottom layer having subwavelength grating. For a forward incidence, the metal-insulator-metal (MIM) structure operates as a gap plasmonic cavity if the linearly polarized (LP) component is parallel to the grating wires. It also acts as a high-efficiency dual-layer grating polarizer for the orthogonal LP component. For the backward incidence, the high reflectance of the grating blocks the function of the gap plasmonic cavity, leading to its pure functioning as a polarizer. A bifunctional Janus metasurface for 45 degrees beam deflector and polarizer, with a transmission of 0.87 and extinction ratio of 3840, is designed at 1.55 µm and is investigated to prove the validity of the proposed strategy. Moreover, the proposed metasurface can be cascaded to achieve more flexible functions since these functions are independent in terms of operational mechanism and structural parameters. A trifunctional Janus metasurface that acts as a focusing lens, as a reflector, and as a polarizer is designed based on this strategy. The proposed metasurface and the design strategy provide convenience and flexibility in the design of multifunctional, miniaturized, and integrated optical components for polarization-related analysis and for detection systems.

High-Performance and Reliable Silver Nanotube Networks for Efficient and Large-Scale Transparent Electromagnetic Interference Shielding.

The development of flexible and transparent electromagnetic interference (EMI) shielding materials with excellent comprehensive properties is urgently demanded as visual windows and display devices in aeronautic, industry, medical, and research facilities. However, the method of how to obtain highly efficient and reliable transparent EMI shielding devices is still facing lots of obstacles. Here, a high-performance silver nanotube (AgNT) network with stable and integrated interconnects is prepared by physical depositing technology, based on a uniform and large-scale nanofiber skeleton. This unique structure enables the AgNT network to achieve one order higher conductivity (∼1.0 Ω/sq at >90% transmittance) than previous research studies and keeps <10% variation with random deformations (>5000 times). Moreover, the manufactured AgNT shielding film with a thickness of less than 1 mm can be easily transferred to arbitrary surfaces as a transparent and flexible EMI shielding film at commercial ∼35 dB EMI shielding effectiveness, with large-scale, low-cost, and simple preparation processes. These excellent properties endow the AgNT shielding film to achieve great potential for future flexible and transparent scenarios.

Single-Layer MoS2 Mechanical Resonant Piezo-Sensors with High Mass Sensitivity.

Thin-film resonators and scanning probe microscopies (SPM) are usually used on low-frequency mechanical systems at the nanoscale or larger. Generally, off-chip approaches are applied to detect mechanical vibrations in these systems, but these methods are not much appropriate for atomic-thin-layer devices with ultrahigh characteristic frequencies and ultrathin thickness. Primarily, those mechanical devices based on atomic-layers provide highly improved properties, which are inapproachable with conventional nanoelectromechanical systems (NEMS). In this report, the assembly and manipulation of single-atomic-layer piezo-resonators as mass sensors with eigen mechanical resonances up to gigahertz are described. The resonators utilize electronic vibration transducers based on piezo-electric polarization charges, allowing direct and optimal atomic-layer sensor exports. This direct detection affords practical applications with the previously inapproachable Q-factor and sensitivity rather than photoelectric conversion. Exploration of a 2406.26 MHz membrane vibration is indicated with a thermo-noise-limited mass resolution of ∼3.0 zg (10-21 g) in room temperature. The fabricated mass sensors are contactless and fast and can afford a method for precision measurements of the ultrasmall mass with two-dimentional materials.

Large-area, lithography-free, narrow-band and highly directional thermal emitter.

Thermal radiation with narrow bandwidth and well-defined emission directions is highly sought after for a variety of applications, ranging from infrared sensing and thermal imaging to thermophotovoltaics. Here, a large-area (4-inch-diameter) long-wavelength infrared thermal emitter is presented, which is spectrally selective, highly directional, and easily fabricated. The basic structure of the proposed thermal emitter is composed of a truncated one-dimensional photonic crystal and a continuous metallic film separated by a dielectric spacer. Experimental results show that the emitter exhibits a narrowband thermal emittance peak of 92% in the normal direction at the wavenumber of 943.4 cm-1 with a bandwidth of 12.5 cm-1 and a narrow angular emission lobe with a limited solid angle of 0.325 sr (0.115 sr) for s (p) polarization. Numerical simulation analyses are performed to corroborate the experimental observations. Temporal coupled-mode theory combined with transfer matrix method is employed to analytically investigate the emission properties of the structure, which not only can be used to understand the experimental results, but also plays a certain guidance role in designing a thermal emitter with the desired properties. The present thermal emitter can be implemented for thermal photonics management, allowing applications in thermal imaging and medical systems, etc.

Decreased serum complement component 4 levels in patients with schizophrenia.

Dysregulation of the immune system in mental disease, particularly complement component 4 (C4), which may be associated with schizophrenia, has been repeatedly observed. This study investigated the association between the level of serum component 4 and schizophrenia. Data were derived from a case-control association study of 40 unrelated adult patients with schizophrenia and 40 matched healthy controls. The component 4 level in serum was measured for comparative analysis by a component 4 enzyme-linked immunosorbent assay kit. Our findings suggest that the serum component 4 level is lower in patients with schizophrenia than in the controls, and the results apply to both males and females. Our results will lay an important foundation for establishing diagnostic methods and provide feasible and reliable evidence for the clinical treatment of schizophrenia.

High-Efficiency and Wide-Angle Versatile Polarization Controller Based on Metagratings.

Metamaterials with their customized properties enable us to efficiently manipulate the polarization states of electromagnetic waves with flexible approaches, which is of great significance in various realms. However, most current metamaterial-based polarization controllers can only realize single function, which has extremely hindered the expansion of their applications. Here, we experimentally demonstrate highly efficient and multifunctional polarization conversion effects using metagrating by integrating single-structure metallic meta-atoms into the dielectric gratings. Benefiting from the combined advantages of the gratings and the metamaterials, the considered metagrating can operate in transmission and reflection modes simultaneously, acting as a high-performance and wide-angle quarter-wave or half-wave plate with distinct functions in different frequency bands. This metagrating structure is scalable to other frequency ranges and may provide opportunities to design compact multifunctional optical polarization control devices.

Broadband circular polarizers constructed using helix-like chiral metamaterials.

In this paper, one kind of helix-like chiral metamaterial which can be realized by multiple conventional lithography or electron beam lithographic techniques is proposed to have a broadband bianisotropic optical response analogous to helical metamaterials. On the basis of twisted metamaterials, via tailoring the relative orientation within the lattice, the anisotropy of arcs is converted into magneto-electric coupling of closely spaced arc pairs, which leads to a broad bianisotropic optical response. By connecting the adjacent upper and lower arcs, the coupling of metasurface pairs is transformed into the coupling of the three-dimensional inclusions, and provides a much broader and higher bianisotropic optical response. For only a four-layer helix-like metamaterial, the maximum extinction ratio can reach 19.7. The operation band is in the wavelength range of 4.69 µm to 8.98 µm with an average extinction ratio of 6.9. And the transmittance for selective polarization is above 0.8 in the entire operation band. Such a structure is a promising candidate for integratable and scalable broadband circular polarizers, especially it has great potential to act as a broadband circular micropolarizer in the field of the full-Stokes division of focal plane polarimeters.

Giant and broadband circular asymmetric transmission based on two cascading polarization conversion cavities.

In this paper, a three-layered sandwiched metamaterial is proposed to achieve giant and broadband asymmetric transmission of circularly polarized waves at the near-infrared communication band. The metamaterial consists of two layers of identical 45° tilted chiral S-shaped metasurfaces sandwiched with a subwavelength metallic grating. Based on the delicate combination of broadband polarization conversion and a cavity-enhanced effect, the asymmetric parameter can reach a maximum value of 0.87 and over 0.6 in a wide range from 1.2 to 2.0 µm, which has not been found in previous reports. Furthermore, a perfect robustness to misalignments is obtained as the effect originated from function-independent cascading cavities, which effectively reduce the requirement of alignment precision in layer-by-layer photolithography processes. The proposed nanostructure has a great potential to be used as a circular polarization rotator or diode-like device in optical communication systems.

Colorful solar selective absorber integrated with different colored units.

Solar selective absorbers are the core part for solar thermal technologies such as solar water heaters, concentrated solar power, solar thermoelectric generators and solar thermophotovoltaics. Colorful solar selective absorber can provide new freedom and flexibility beyond energy performance, which will lead to wider utilization of solar technologies. In this work, we present a monolithic integration of colored solar absorber array with different colors on a single substrate based on a multilayered structure of Cu/TiN(x)O(y)/TiO(2)/Si(3)N(4)/SiO(2). A colored solar absorber array with 16 color units is demonstrated experimentally by using combinatorial deposition technique via changing the thickness of SiO(2) layer. The solar absorptivity and thermal emissivity of all the color units is higher than 92% and lower than 5.5%, respectively. The colored solar selective absorber array can have colorful appearance and designable patterns while keeping high energy performance at the same time. It is a new candidate for a number of solar applications, especially for architecture integration and military camouflage.

[Preparation of Tb3+, Yb3+ doped Y2O3 luminescent powders and near-infrared quantum cutting research].

Y2O3:Tb3+ and Y2O3:Tb3+, Yb3+ samples were prepared by co-precipitation method. The morphology, microstructure and fluorescence spectra at room temperature of samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and fluorescence spectrometer, The optimal process conditions of Y2O3:Tb3+ under different doping concentrations, annealing temperature, and pH value of the solution were obtained: Tb3+ concentration is 1.5%, annealing temperature is 1400 degrees C, an alkaline solution environment, and samples under 300 nm light excitation have the largest green light emission at 543 nm. The corresponding relation of Tb3+ ion level structure and transition properties and experimental spectra were analyzed in detail, and we explained the influence mechanism of process conditions and the fluorescence quenching process mainly effects luminous intensity of samples. The energy transfer from sensitizing ions Tb3+ to active ion Yb3+ was confirmed, it made the sample have considerable emitting light in the near-infrared region; the authors described the process of cooperation conversion luminescence between the two ions from the level transition angle, and also analyzed the system of fluorescence quenching process. Test results showed that the near infrared quantum cutting can effectively improve the luminous efficiency of doped ions, and will have broad application prospects in the silicon solar cells and other fields.

Synthesis and properties of core-shell SiO2@Y2O3:Eu3+ wavelength conversion materials.

In this paper, with spherical SiO2 particles fabricated via Stöber method, monodispersed and uniform SiO2 @Y2O3:Eu3+ core-shell submicrospheres were prepared through a simply homogeneous precipitation method. SEM, TEM and XRD analysis indicated that the as-prepared samples were uniform and well monodispersed spheres. The SiO2 core was perfectly coated by the shell composed of cubic crystalline Y2O3:Eu3+ and the thickness of the shell was about 26 nm. Photoluminescence spectra showed that the luminescence efficiency was improved remarkably after being coated on the SiO2 core. The 3D PL spectra showed that almost all UV photons in the range from 200 nm to 400 nm can be converted to visible photons by the as-prepared samples. Results showed that when the SiO2 core was synthesized in the TEOS single feeding model with the amount of core being 0.4 g, doping concentration being 4% and annealing at 800 degrees C, the sample has the best performance on luminescence. By dispersing the as-prepared sample in the anti-reflection sol to prepared the wavelength conversion and anti-reflection film and apply it to the silicon solar cell, the photoelectric conversion efficiency can be increased by 7.41% in maximum.

Preparation of 3D network Na2Ti2O4(OH)2 nanotube film and study on formation mechanism of nanotubes and light absorption properties.

The 3D network Na2Ti2O4(OH)2 nanotube film was prepared by combining interface chemical reaction with hydrothermal reaction. It can be readily indexed based on an orthorhombic system Na2Ti2O4(OH)2 (JCPDS, 47-0124), corresponding with (200), (110), (600), and (020). The nanotubes are commonly multiwalled with a diameter about 40 nm, and a length more than 2000 nm. The interlamellar space of the nanotubes is about 0.9 nm, and these nanotubes loaded with silver exhibit a strong UV-Vis-NIR absorption from 200 nm to 1000 nm, with a resonance-absorption peak at 490 nm. In addition, the formation mechanism of 3D network Na2Ti2O4(OH)2 nanotube film was investigated, the formation mechanism can be expressed as follows: Ti --> TiCl3 --> TiO2(anatase) --> Na2Ti2O4(OH)2(nanotube).