Passive Materials Research Articles

Intelligent metasurfaces: control, communication and computing

AbstractControlling electromagnetic waves and information simultaneously by information metasurfaces is of central importance in modern society. Intelligent metasurfaces are smart platforms to manipulate the wave–information–matter interactions without manual intervention by synergizing engineered ultrathin structures with active devices and algorithms, which evolve from the passive composite materials for tailoring wave–matter interactions that cannot be achieved in nature. Here, we review the recent progress of intelligent metasurfaces in wave–information–matter controls by providing the historical background and underlying physical mechanisms. Then we explore the application of intelligent metasurfaces in developing novel wireless communication architectures, with particular emphasis on metasurface-modulated backscatter wireless communications. We also explore the wave-based computing by using the intelligent metasurfaces, focusing on the emerging research direction in intelligent sensing. Finally, we comment on the challenges and highlight the potential routes for the further developments of the intelligent metasurfaces for controls, communications and computing.

Dynamically tunable second-harmonic generation using hybrid nanostructures incorporating phase-change chalcogenides

Abstract Nonlinear metasurfaces with high conversion efficiencies have been vastly investigated. However, strong dynamic tunability of such devices is limited in conventional passive plasmonic and dielectric material platforms. Germanium antimony telluride (GST) is a promising phase-change chalcogenide for the reconfiguration of metamaterials due to strong nonvolatile changes of the real and imaginary parts of the refraction index through amorphous-crystalline phase change. The orderly structured GST has an even higher potential in tunable second-harmonic generation (SHG) with a non-centrosymmetric crystal structure at the crystalline phase, while the amorphous phase of GST does not exhibit bulk second-order nonlinearity. Here, we experimentally demonstrate SHG switches by actively controlling the crystalline phase of GST for a GST-based hybrid metasurface featuring a gap-surface plasmon resonance, and a quarter-wave asymmetric Fabry–Perot (F–P) cavity incorporating GST. We obtain SHG switches with modulation depths as high as ∼ 20 dB for the wavelengths at the on-state resonance. We also demonstrate the feasibility of multi-level SHG modulation by leveraging three controlled GST phases, i.e., amorphous, semi-crystalline, and crystalline, for the gap-surface plasmon hybrid device, which features stronger light–matter interaction and has higher resonant SHG efficiencies than the asymmetric F–P cavity device at respective GST phases. This research reveals that GST-based dynamic SHG switches can be potentially employed in practical applications, such as microscopy, optical communication, and photonic computing in the nonlinear regime.

Suppressed recombination for monolithic inorganic perovskite/silicon tandem solar cells with an approximate efficiency of 23%

Potentially temperature-resistant inorganic perovskite/silicon tandem solar cells (TSCs) are promising devices for boosting efficiency past the single-junction silicon limit. However, undesirable non-radiative recombination generally leads to a significant voltage deficit. Here, we introduce an effective strategy using nickel iodide, an inorganic halide salt, to passivate iodine vacancies and suppress non-radiative recombination. NiI2-treated CsPbI3-xBrx inorganic perovskite solar cells with a 1.80 ​eV bandgap exhibited an efficiency of 19.53% and a voltage of 1.36 ​V, corresponding to a voltage deficit of 0.44 ​V. Importantly, the treated device demonstrated excellent operational stability, maintaining 95.7% of its initial efficiency after maximum power point tracking for 300 ​h under continuous illumination in a N2 atmosphere. By combining this inorganic perovskite top cell with a narrower bandgap silicon bottom cell, we for the first time achieved monolithic inorganic perovskite/silicon TSCs, which exhibited an efficiency of 22.95% with an open-circuit voltage of 2.04 ​V. This work provides a promising strategy for using inorganic passivation materials to achieve efficient and stable solar cells.

Study on Electrical Parameter Matching of Piezoelectric Stack Periodic Strut for Helicopter Cabin Noise Control

The gear meshing noise generated by the helicopter main reducer is one of the important sources of noise in the helicopter cabin. By improving the isolation performance of the struts supporting reducer to the gear meshing vibration, the purpose of reducing the gear meshing noise in the helicopter cabin can be achieved. Piezoelectric stack periodic strut (PSPS) composed of piezoelectric stacks and passive materials periodically arranged is an original type of strut with active and passive hybrid isolation characteristics. Piezoelectric stacks and passive materials form a periodic structure, which makes PSPS have a unique stopband characteristic. The propagation of elastic waves in the stopband frequency range is attenuated, which can improve the broadband passive vibration isolation capability of the PSPS; The piezoelectric stacks can adjust the elastic wave propagation in the PSPS and improve the single-frequency or multifrequency active isolation performance of the PSPS. Since the driving voltage and current range of the piezoelectric stacks significantly affect the isolation performance of the PSPS, this article focuses on the relationship between the isolation performance of the PSPS and the voltage and current required by the piezoelectric stacks. Firstly, based on the passive material periodic structure transfer matrix model, the driving voltage and current of the piezoelectric stacks are introduced into the model, and a PSPS electromechanical coupling model based on the transfer matrix form is established. Secondly, the correctness of the model is verified by the finite element software. Based on the model, the design process of PSPS parameters is proposed. The optimal isolation performance of PSPS is predicted under the limitation of maximum driving voltage and current. The effects of damping loss factor, exciting force, period number and passive material on the requirements of electrical parameters for active control are studied. A three-period PSPS strut composed of piezoelectric stack actuator and PV strut is used for experimental research, and the matching of electrical parameters of this PSPS in the test is analyzed.

Hysteresis‐Free Planar Perovskite Solar Module with 19.1% Efficiency by Interfacial Defects Passivation

In few years, perovskite solar devices have reached high efficiency on lab scale cells. Upscaling to module size, effective perovskite recipe and posttreatment are of paramount importance to the breakthrough of the technology. Herein this work, the development of a low‐temperature planar n–i–p perovskite module (11 cm2 aperture area, 91% geometrical fill factor) is reported on, exploiting the defect passivation strategy to achieve an efficiency of 19.1% (2% losses stabilized) with near‐zero hysteresis, that is the most unsolved issue in the perovskite photovoltaic technology. The I/Br (iodine/bromide) halide ion ratio of the triple‐cation perovskite formulation and deposition procedure are optimized to move from small area to module device and to avoid the detrimental effect of dimethyl sulfoxide (DMSO) solvent. The organic halide salt phenethylammonium iodide (PEAI) is adopted as surface passivation material on module size to suppress perovskite defects. Finally, homogeneous and defect‐free layers from cell to module with only 8% relative efficiency losses, high reproducibility, and optimized interconnections are scaled by laser ablation methods. The homogeneity of the perovskite layers and of the full stack was assessed by optical, morphological, and light beam–induced current (LBIC) mapping characterizations.

Synergistic Repair Effect of Calcite-Based Passivator and Low-Accumulation Maize

In this study, a field experiment of soil passivation and low accumulation-crops was carried out for typical northern alkaline cadmium and lead compound-polluted farmland soil. Calcite was used as the main passivation material, and a small amount of slaked lime, zeolite powder, and biochar were combined to form a group passivation agent. The effects of passivators on soil physicochemical properties, bioavailability of the heavy metals Cd and Pb, and the yield and plant (stalk and seed) content of heavy metals Cd and Pb in low-accumulation maize were investigated under different grouping conditions of calcite+slaked lime (CL), calcite+zeolite (CZ), calcite+biochar (CB), and calcite+slaked lime+zeolite+biochar (CLZB). The results showed that:① all applications of passivating agent ensured the normal growth of maize and slightly increased the 1000 grain weight and maize yield. ② The effects of different calcite-based passivators on soil physical and chemical properties were different. The CL, CZ, CB, and CLZB treatments increased soil pH by 0.46, 0.25, 0.12, and 0.13 units, respectively, but had no significant correlation with soil fertility index (P>0.05). ③ DTPA leaching and ion exchange state contents of Cd and Pb in soil could be significantly reduced by different calcite-based combinations with passivators, and the reduction rates of Cd and Pb in DTPA leaching were 49.36% and 72.55%, respectively. The reduction rates of ion exchange Cd and Pb contents were 55.39% and 78.52%, respectively. ④ The contents of Cd and Pb in stems, leaves, and grains of low-accumulation maize were further reduced by different passivating agents. The contents of Cd and Pb in the stems and leaves of maize were reduced by 45.93% and 67.00% after CLZB treatment, and the contents of Cd and Pb in grains were decreased by 25.17% and 46.62%, respectively. Moreover, the contents of Cd and Pb in DTPA extraction and ion exchange states were significantly positively correlated with the contents of Cd and Pb in corn stems, leaves, and grains (P<0.01). The results showed that the combined use of combination passivators and low-accumulation crop varieties can obtain better restoration effects in the remediation of cadmium and lead combined-polluted farmland in the middle alkaline soil in northern China.

Aerogel-based ultralight noise absorbers fabricated using 3D freeze printing

Aerogels are a group of synthetic materials with a structure comprising up to 99.8% air. This ultra-sparse skeletal structure results in extremely low-density and thermal conductivity. Because of these extreme properties, aerogels are highly attractive for thermal insulation and energy absorption applications. In acoustics, their application is typically limited to their use as granular material—either as granular layers or as additives to conventional fibrous and matrix materials. Here, we explore the possibility of controlling not only their mesostructure but also their macrostructure by fabricating aerogel-based ultralight noise absorbers using a 3-D Freeze Printing (3DFP) technique. First, we introduce the novel 3DFP method, which combines the advantages of additive manufacturing and freeze casting processes. Next, we focus on the acoustic characterization of 3-D freeze printed aerogels using a normal incidence impedance tube setup. Our results show that compared with current passive noise reduction materials, the unique structures generated by the 3DFP method can provide significantly improved absorption and transmission loss properties.

Cover Image

The cover image is based on the Basic Research Multiscale modeling of passive material influences on deformation and force output of skeletal muscles by Xiaolong He et al., https://doi.org/10.1002/cnm.3571.

Realism and Power in Mark Twain's

Realism and Power in Mark Twain's

Synergistic effect of amide and fluorine of polymers assist stable inverted perovskite solar cells with fill factor > 83%

Exploring hole transporting materials (HTMs) with defect passivation function is an effective way to suppress the defect-induced non-radiative recombination (NRR) process in perovskite solar cells (PSCs). To date, most of these passivation materials are mainly devoted to passivate the uncoordinated Pb2+ of perovskite layer. However, ion migration processes of MA+ and I- in PSCs also cause a series of negative effects, which severely deteriorate the efficiency and device stability. Thus far, very few HTMs that can simultaneously passivate both the MA+/Pb2+ cations and I- anion defects in ABX3 structured perovskite. Herein, three dopant-free HTMs (BNs, BNs-F, and BNo-F) featuring multisite defect passivation function were developed for inverted PSCs. The carbonyl groups C = O and N–H in the amide linkers of BNs-F contributed to passivate the uncoordinated Pb2+ and the halide related defects, respectively. Simultaneously, the F atoms in bridges could interact with MA+ in perovskite via N-H‧‧‧F bond. Interestingly, an intermolecular hydrogen bond (O = C-N-H‧‧‧F) between amide linkers and F atoms was found in our work, which enabled BNs-F to achieve a high hole mobility of 2.42 × 10-4 cm2 V−1 s−1. Consequently, benefiting from the alleviated NRR behavior and enhanced charge transport ability, the optimized devices based on BNs-F realized a remarkable fill factor of 0.834, accompanying a champion efficiency up to 20.56% with superior long-term stability, exceeding those with BNs (19.03%), BNo-F (19.07%) and PTAA (19.56%). Our findings provide a guidance for design molecules with comprehensive passivation effect on MA+/Pb2+/I- defects to achieve efficient and stable PSCs.

Programmable Multiwavelength Radio Frequency Spectrometry of Chemophysical Environments through an Adaptable Network of Flexible and Environmentally Responsive, Passive Wireless Elements

Readout of multiparametric environmental signals typically uses discrete sensing formats that individually require unique signal conditioning circuitry and/or processing pathways. Here, adaptable sensor networks composed exclusively of passive material architectures that enable spectrometric comonitoring of chemical or physical environmental signals are proposed. Herein, a single radio frequency (RF) reader wirelessly interacts first with an intermediate wireless relay coil—this is tunable in length and can be designed to conform around surfaces. This relay (that is fused on textiles or surfaces) is then wirelessly coupled to arrays of passive RF sensors with individually programmable flexibility/reactivity to environmental signals. Multiple chemical and physical signals can then be monitored within the single spectral readout of a wearable reader. This technique can probe over tunable length scales, and is robust to mechanical disturbances that limit present techniques. As a proof of concept, this approach is used to comonitor chemophysical metrics such as nutrients, temperature, pressure, pH, and more on the skin or in utensils with a single readout. This technique may form a cornerstone of zero‐microelectronic sensor networks.

Efficient and stable TiO2 nanorod array structured perovskite solar cells in air: Co-passivation and synergistic mechanism

In recent years, single crystal TiO2 nanorod arrays (TNRAs) with fewer grain boundaries for photo-generated electron transport and ordered channel structures for perovskite filling have been employed as electron transport layers for efficient perovskite solar cells (PSCs). However, further improvements in TNRA-based PSC performance are urgently needed because defects in the perovskite layer seriously hinder device efficiency and stability. In this study, with TNRAs as the electron transport layer, CH3NH3PbI3 (MAPbI3) perovskite films were prepared in air by a two-step spin coating method. The grain boundary defects and surface defects of the MAPbI3 layer are co-passivated by octyl ammonium iodide (CH3(CH2)7NH3I, OAI) and choline chloride (HOCH2CH2N(CH3)3Cl, Ch), respectively, and the effects of the two passive materials on the power conversion efficiency (PCE) and stability of TNRA-based PSCs are systematically investigated. The results reveal that the introduction of OAI facilitates the formation of intermolecular valence bonds between crystalline MAPbI3 to enhance its structural stability, while Ch passivates the Pb–I antisite substitution defect and I− vacancy defect on the perovskite film surface. Compared with the pristine device, the optimal PCE of the passivated device increases from 18.86% to 20.08%, and the thermal, humid and long-term stability of the device is also improved.

The performance and mechanism of cadmium availability mitigation by biochars differ among soils with different pH: Hints for the reasonable choice of passivators

The performances of passivation materials mitigating Cadmium (Cd) bioavailability considerably vary with the pH condition of Cd-contaminated soils. However, less information was available for the method of improving Cd passivation efficiency taking into account the pH of the targeted soil. Furthermore, the underlying mechanism of Cd availability mitigation in soils with different pH has not been clearly explored. In this study, cotton straw biochar (CSB) and its modified products using NaOH (CSB–NaOH) were prepared and applied in two kinds of Cd-contaminated soils with different pH. It was found that CSB-NaOH was more effective than CSB in regulating the Cd bioavailability in the acid soil, while the opposite tendency was observed in alkaline soil. The difference of the Cd passivation efficiency is correlated with contributions of various Cd-biochar binding mechanisms, which cation exchange mechanism is largely eliminated for CSB-NaOH. The interaction of Cd with CSB/CSB-NaOH was further evidenced through characterization results of Scan Electron Microscopy (SEM), X-Ray Diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR) and X-ray Photoelectron spectroscopy (XPS). Characterization results proved that carboxyl, hydroxyl and ethyl groups were the key functional groups involved in Cd passivation. XPS results showed that Cd binding methods varied between CSB and CSB-NaOH, which Cd2+ and Cd–O were the main form of Cd binding to CSB while Cd–O was the main form on CSB-NaOH. In this work, it was demonstrated that in acid soil, pH change caused by biochar plays a more significant role in controlling the Cd bioavailability, while in alkaline soil, the strength of the Cd-biochar interaction is more decisive for the Cd passivation efficiency. This work provides information on how to select the suitable passivator to decrease the Cd bioavailability in terms of different soil pH and property.

Immobilization of cadmium in river sediment using phosphate solubilizing bacteria coupled with biochar-supported nano-hydroxyapatite

Cadmium pollution in river sediment is serious and single remediation method is difficult to deal with. Thus, it is extremely urgent to remediate Cd contaminated river sediments. A new remediation system with phosphate solubilizing bacteria (PSBs) and biochar supported nano-hydroxyapatite (nHAP@BC) was provided to enhance the immobilization efficiency of Cd in this research. The passivation effect of PSB + nHAP@BC under different conditions and its mechanism were investigated. The results showed that the highest Cd2+ immobilization efficiency could reach 90% in the liquid medium when using PSB cooperated with 5:1 nHAP@BC in the condition of temperature 15–37 °C, pH = 7, initial Cd2+ concentration less than 0.5 mM. Meanwhile, the characterization results of XRD and FT-IR showed that Cd might exist in the form of Cd-HAP containing CdPO4. Furthermore, the simulated sediment remediation experiment indicated that the acid soluble fraction of Cd was reduced by 28% and transferred to the residual fraction. This work demonstrated that PSBs cooperated with nHAP@BC was an excellent candidate of passivation material for sediment Cd and could be considered as an effective way for immobilizing Cd in the future.

Role of zinc tin oxide passivation layer at back electrode interface in improving efficiency of Cu2ZnSn(S,Se)4 solar cells

We report a Cu2ZnSn(S,Se)4 (CZTSSe) solar cell with a modified structure via inserting an intermediate zinc tin oxide (ZTO) layer between Mo electrode and CZTSSe layer in the conventional CZTSSe solar cell. Comparing with the conventional CZTSSe solar cells (without ZTO layer), the best photovoltaic performance is obtained for the solar cells with a modified structure. When an 8-nm-thick ZTO passivation layer is inserted, the corresponding device shows the improvements in performance parameters, including short-circuit current density (JSC), open-circuit voltage (VOC), and fill factor (FF). As a result, we obtained a maximum power conversion efficiency (PCE) of 8.95% for the optimized device with an 8-nm-thick ZTO layer, which is ascribed to the increase of shunt resistance (RSh), decrease of series resistance (RS) and decrease of reverse saturation current density (J0). Our results suggest that the ZTO is a promising passivation material at back electrode interface for optimizing the performance and improving efficiency of CZTSSe-based solar cells.

Difluorobenzylamine Treatment of Organolead Halide Perovskite Boosts the High Efficiency and Stability of Photovoltaic Cells.

As one of the most competitive light-harvesting materials, organometal halide perovskites have attracted great attention due to their low-cost and top-down solution fabricability. However, the instability of perovskites in a moist environment reduces the potential for their commercialization. In this study, novel 2,4-fluorobenzylamine (FBA) was employed as the passivation material, which could successfully suppress the defects and improve the moisture resistance of perovskites, resulting in an ultrahigh power conversion efficiency of 17.6% for the carbon-based perovskite solar cells with good stability. Meanwhile, the whole process of interactions between the H2O molecule and the perovskite lattice was first elucidated by density functional theory calculations, which demonstrated the underlying mechanism of the improvement of moisture stability with the FBA treatment. This work opens up a new route toward addressing the main obstacles in the practical application of perovskite devices under ambient conditions.

Experimental Setup for Irradiation of Cell Cultures at L2A2

Laser–plasma proton sources and their applications to preclinical research has become a very active field of research in recent years. In addition to their small dimensions as compared to classical ion accelerators, they offer the possibility to study the biological effects of ultra-short particle bunches and the correspondingly high dose rates. We report on the design of an experimental setup for the irradiation of cell cultures at the L2A2 laboratory at the University of Santiago de Compostela, making use of a 1.2 J Ti: Sapphire laser with a 10 Hz repetition rate. Our setup comprises a proton energy separator consisting of two antiparallel magnetic fields realized by a set of permanent magnets. It allows for selecting a narrow energy window around an adaptable design value of 5 MeV out of the initially broad spectrum typical for Target Normal Sheath Acceleration (TNSA). At the same time, unwanted electrons and X-rays are segregated from the protons. This part of the setup is located inside the target vessel of the L2A2 laser. A subsequent vacuum flange sealed with a thin kapton window allows for particle passage to external sample irradiation. A combination of passive detector materials and real-time monitors is applied for measurement of the deposited radiation dose. A critical point of this interdisciplinary project is the manipulation of biological samples under well-controlled, sterile conditions. Cell cultures are prepared in sealed flasks with an ultra-thin entrance window and analysed at the nearby Fundación Pública Galega Medicina Xenómica and IDIS. The first trials will be centred at the quantification of DNA double-strand breaks as a function of radiation dose.

Roles of Long‐Chain Alkylamine Ligands in Triple‐Halide Perovskites for Efficient NiOx‐Based Inverted Perovskite Solar Cells

The passivation of perovskite bulk and heterointerface defects is one of the most significant ways to enhance the efficiency and operational stability of perovskite solar cells (PSCs). So far, ammonium‐based alkylamine halides have been considered as effective passivation materials to reduce defects of the perovskite absorber layer. Herein, roles of long‐chain alkylamine ligands (LALs) in triple‐halide perovskites are systematically studied for achieving efficient NiOx‐based inverted PSCs. Two kinds of LALs oleylammonium (OAm) and phenethylammonium (PEA), as perovskite bulk and interface passivation agents, respectively, are introduced. It is found that both OAm and PEA ligands cannot only assist their crystal growth with vertical orientation, but also suppress triple‐halide perovskite bulk and interface defects. As precursor additives, OAm ligands can be used as organic spacers to assist the generation of the 2D@3D perovskite bulk crystals. 2D@3D/2D perovskite heterostructures are further formed when the 2D@3D perovskite bulk film is post‐treated by PEA ligands. As a result, such strategies enable hysteresis‐free and highly efficient NiOx‐based triple‐halide inverted PSCs.

In Situ Calibration of Passive Samplers for Viruses in Wastewater

Wastewater surveillance for SARS-CoV-2 RNAhas rapidly developed worldwide. In low-prevalence settings, sampling in sewage networks is proposed to monitor community transmission. Passive samplers are cost-effective and suitable for catchments where autosamplers cannot be operated. This resulted in their pioneering applications in some countries, even though their sampling kinetics for viruses remains unclear. We conducted in situ calibration of passive sampling materials (membranes, swabs, gauzes, and tampons) for the uptake of pepper mild mottle virus (PMMoV), enterovirus, and human adenovirus 40/41. Passive samplers were deployed in wastewater influent and retrieved sequentially over 48 h. Membranes performed continuous sampling over 48 h with estimated linear sampling rates of 1 mL h–1 for PMMoV, 0.3 mL h–1 for enterovirus, and 33.1 mL h–1 for adenovirus. Tampons and swabs showed a rapid initial uptake of viruses and reached equilibrium after 8 h, while gauze uptake rates were potentially confounded by either inhibitors or viral losses during extended exposure. Additionally, monitoring SARS-CoV-2 at 17 sewer manholes showed that the detection ratio of membranes (14 of 17) was higher than that of tampons (8 of 17). This study demonstrated the ability of passive samplers to retain viral fragments, making them a practical tool for wastewater surveillance for the detection of disease outbreaks in communities.

Multiscale modeling of passive material influences on deformation and force output of skeletal muscles.

Passive materials in human skeletal muscle tissues play an important role in force output of skeletal muscles. This paper introduces a multiscale modeling framework to investigate how age-associated variations on microscale passive muscle components, including microstructural geometry (e.g., connective tissue thickness) and material properties (e.g., anisotropy), influence the force output and deformations of the continuum skeletal muscle. We first define a representative volume element (RVE) for the microstructure of muscle and determine the homogenized macroscale mechanical properties of the RVE from the separate mechanical properties of the individual components of the RVE, including muscle fibers and connective tissue with its associated collagen fibers. The homogenized properties of the RVE are then used to define the elements of the continuum muscle model to evaluate the force output and deformations of the whole muscle. Conversely, the regional deformations of the continuum model are fed back to the RVE model to determine the responses of the individual microscale components. Simulations of muscle isometric contractions at a range of muscle lengths are performed to investigate the effects of muscle architectural changes (e.g., pennation angles) due to aging on force output and muscle deformation. The correlations between the pennation angle, the shear deformation in the microscale connective tissue (an indicator for the lateral force transmission), the angle difference between the fiber direction and principal strain direction and the resulting shear deformation at the continuum scale, as well as the force output of the skeletal muscle are also discussed.