Asymmetrical Chirality in 3D Bended Metasurface

Chiral metasurfaces offer crucial opportunities to expand the application potential for chiral photonics, but its desired freely structural control and giant circular dichroism (CD) allow for more and greater challenges. Here, different from previous metasurfaces with single structural regulation, a kind of bifunctional chiral metasurface based on 3D bended asymmetric construction is proposed, which shows giant CD combined with asymmetric chirality at 5.2 µm. The bended metasurface with abundant spatial freedom, consisting of an array of asymmetric bended split ring resonators (SRRs), can be built up from the tensile stress induced by focused ion beam (FIB)–matter interaction. The results show that the CD increases with the bending angle of the metasurface and reaches a maximum at a bending angle of 60°. Particularly, it is found that the CD is 0.71/0.85 (experiment/simulation) for the backward incidence but −0.29/−0.29 for the forward incidence, indicating that the giant CD and asymmetric chirality properties are realized simultaneously in the same metasurface. The calculated results of near-field distribution and the electric/magnetic dipoles show that the giant CD and the asymmetric chirality come from $\text{◂≠▸}\overrightarrow{p}\cdot \overrightarrow{m}\ne 0$ and $\text{◂...▸}|\overrightarrow{p}\times \overrightarrow{m}|\ne 0$, respectively. The findings inspire a high efficiency approach to design multifunctional chiral optical devices.     

Engineering Nanoclay Edges to Enhance Antimicrobial Property against Gram-Negative Bacteria: Understanding the Membrane Destruction Mechanism by Contact-Kill

The overuse or abuse of antibiotics has led to serious health problems. During the recent decades, among the various methods used in antibacterial applications, some nanoclay minerals are proved antibacterial or inhibitory to the bacterial growth. However, the antibacterial mechanism of contact-kill based on the intrinsic structure of nanoclays is still unclear. Here, the antibacterial ability of pure clay is enhanced by creating more edge surfaces on kaolinite (Kaol) and the antibacterial mechanism is clarified at the atomic level. Based on experiments and density functional theory/molecular dynamics  calculations, the positively charged Al (OH) and Al (OH₂) species on the edge surfaces of Kaol are confirmed to kill the Escherichia coli cells through direct contact by destroying their outer membrane (OM). The strong hydrogen bonding and van der Waals forces between OM and (110)/(1$\overline{1}$0) surfaces of Kaol lead to the folding of OM. Simultaneously, the proton-coupled electron transfer between Lipopolysaccharide (LPS) and (1$\overline{1}$0) edge surface of Kaol causes the dissociation of phosphoryl groups on LPS. Considering the similarities of most nanoclays on their edge surfaces, this finding may shed some light on the development of new nanoclay-based antibacterial materials in the future.     

Finite-Temperature Dynamics in Cesium Lead Iodide Halide Perovskite

Lattice dynamics are often regarded as signatures of the underlying crystal structure. Here, a first-principle-based effective Hamiltonian method combined with molecular dynamics simulations is used to study dynamical behaviors of CsPbI₃ perovskite across temperature and structural phase transitions. A single (short-range tilting) parameter in this effective Hamiltonian is varied in order to make the temperature range of the intermediate tetragonal P4/mbm phase, existing in-between the cubic Pm$\overline{3}$m and orthorhombic Pnma phases, either broader than observed or completely disappearing. Comparing the dynamics of these different cases allows one to conclude that real CsPbI₃ perovskite should have i) two iodine-octahedral-tilt related modes that differ in frequency but both significantly soften as the temperature decreases within the cubic phase toward the Pm$\overline{3}$m-to-P4/mbm transition; and ii) one mode that maintains a very low frequency (of the order of 1.0 cm⁻¹) in the entire region of P4/mbm stability, as a result of the temporal exploration of various structural states. Such latter sub-THz mode mixes fluctuations of antiphase iodine tiltings and Cs antipolar motions because of a trilinear energetic coupling.     

Performance evaluation of nonlinear energy scavenging overlay networks

This paper investigates a nonlinear energy scavenging overlay network (NLESON) wherein a primary source (PS) communicates with a primary destination (PD) probably under aid of a secondary source (SS) who communicates with a secondary destination (SD). SS is a power-constrained device, and thence, its operation relies on energy harvested by a practical nonlinear energy scavenger. To support PS and exploit the harvested energy at most, SS adaptively switches between single and superposition modes where the single mode allows SS to transmit solely its signal with the entire harvested energy and the superposition mode asks SS to transmit both—its signal and amplified primary signal—with different power fractions. Moreover, for increasing the probability of successfully decoding primary signal at PD and SD, which then reduces considerably primary interference on secondary signal in the superposition mode, we leverage both direct channels (PS-PD and PS-SD) and apply both signal combining paradigms (maximum ratio combining and selection combining). The outage/throughput performance of the NLESON is assessed quickly through the proposed closed-form expressions over $\kappa -\mu$ shadowed fading channels. Various results exposed the effectiveness of the aforementioned solutions for the NLESON and their flexibility in controlling system performance.     

Intersymbol interference resilient interleaving architecture for multi-stream interleaved frequency division multiple access system

A multi-stream cyclic interleaving architecture for an interleaved frequency division multiple access (IFDMA) system is proposed. The proposed scheme exploits the full benefits of maximal length sequence ( $m$-sequence), in contrast to single data stream transmission scheme proposed in earlier works, thereby allowing simultaneous transmission of multiple data streams by each user. The cyclic spreading allows the separation of multiple data streams for each user in addition to intersymbol interference (ISI) minimization. The assignment of orthogonal subcarriers to each user compensates multiuser interference (MUI). The increase in the number of data stream transmission improves the data rate of the system. The proposed scheme employs maximal ratio combining (MRC) to maximize the instantaneous signal-to-noise ratio (SNR) of the multipath signal. The performances of the proposed interleaving scheme are compared with the minimum mean square error frequency domain equalization (MMSE-FDE)-based conventional interleaving scheme. Despite the simultaneous transmission of multiple data streams, the proposed scheme retains the performance of single data stream transmission.     

K-submodular function-based service-limit incentive mechanisms for crowd heterogeneous sensing

Recently, crowd sensing, as a new paradigm, uses mobile devices from users to efficiently fulfill allocated tasks, enabling many novel applications such as location sensing and air pollution monitoring. To achieve high-quality service, extensive user participation is crucial. Most of existing works only apply for the homogeneous task scene where the requester has a budget limit and types of sensors used are homogeneous. On the contrary, we investigate a different scenario where the platform has a service limit and types of sensors are heterogeneous. Specially, we design the two service-limit incentive mechanisms, called SCH and SWH, respectively, by minimizing the total cost for a more general case where the value function is monotone $K$-submodular for participatory users so that given services can be fulfilled. The two mechanisms make it possible to extend current small-scale crowd sensing to large-scale crowd sensing, which have the following properties: individual rationality, task feasibility, computational efficiency, truthfulness, and constant frugality. Finally, we use extensive simulations to validate theoretical properties of our mechanisms.     

Robust Surface Reconstruction Induced by Subsurface Ni/Li Antisites in Ni-Rich Cathodes

Loss of active materials is a critical problem of layered oxide cathodes for lithium-ion batteries and undermines their long-term electrochemical performance. However, the atomic-scale outward migration mechanism of transition metals and oxygen remains elusive due to a highly localized environment at surface. Here, the robust surface reconstruction of LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) induced by artificially introduced Ni/Li antisites is reported. Using scanning transmission electron microscopy, the outward co-migration process of nickel and oxygen ions is directly revealed at the atomic scale, finally resulting in a stable surface structure. The robust nature of this surface structure originates from the strong linear superexchange interaction between subsurface Ni_Li and surface Ni as supported by first-principles calculations. An idealized subsurface structure with $\frac{1}{3}$ Ni_Li is designed to suppress the outward migration of transition metal and oxygen ions and provide a universal lattice-coherent surface protection strategy for layered lithium transition metal oxide cathodes.     

Multipoint Defect Synergy Realizing the Excellent Thermoelectric Performance of n‐Type Polycrystalline SnSe via Re Doping

SnSe has attracted much attention due to the excellent thermoelectric (TE) properties of both p‐ and n‐type single crystals. However, the TE performance of polycrystalline SnSe is still low, especially in n‐type materials, because SnSe is an intrinsic p‐type semiconductor. In this work, a three‐step doping process is employed on polycrystalline SnSe to make it n‐type and enhance its TE properties. It is found that the Sn_0.97Re_0.03Se_0.93Cl_0.02 sample achieves a peak ZT value of ≈1.5 at 798 K, which is the highest ZT reported, to date, in n‐type polycrystalline SnSe. This is attributed to the synergistic effects of a series of point defects: $V_{\mathrm{Se}}^{\mathrm{..}},{\mathrm{Cl}}_{\mathrm{Se}}^{.},V_{\mathrm{Sn}}^{,,},{\mathrm{Re}}_{\mathrm{Sn}}^{\times },{\mathrm{Re}}_{}^0$. In those defects, the $V_{\mathrm{Se}}^{\mathrm{..}}$ compensates for the intrinsic Sn vacancies in SnSe, the ${\mathrm{Cl}}_{\mathrm{Se}}^{.}$ acts as a donor, the $V_{\mathrm{Sn}}^{,,}$acts as an acceptor, all of which contribute to optimizing the carrier concentration. Rhenium (Re) doping surprisingly plays dual‐roles, in that it both significantly enhances the electrical transport properties and largely reduces the thermal conductivity by introducing the point defects, ${\mathrm{Re}}_{\mathrm{Sn}}^{\times },{\mathrm{Re}}_{}^0$. The method paves the way for obtaining high‐performance TE properties in SnSe crystals using multipoint‐defect synergy via a step‐by‐step multielement doping methodology.     

Layer Sliding And Twisting Induced Electronic Transitions In Correlated Magnetic 1t-Nbse2 Bilayers

Correlated 2D layers, like 1T-phases of TaS₂, TaSe₂, and NbSe₂, exhibit rich tunability through varying interlayer couplings, which promotes the understanding of electron correlation in the 2D limit. However, the coupling mechanism is, so far, poorly understood and is tentatively ascribed to interactions among the ${\mathrm{d}}_{{\mathrm{z}}^2}$orbitals of Ta or Nb atoms. Here, it is theoretically shown that the interlayer hybridization and localization strength of interfacial Se p_z orbitals, rather than Nb ${\mathrm{d}}_{z^2}$orbitals, govern the variation of electron-correlated properties upon interlayer sliding or twisting in correlated magnetic 1T-NbSe₂ bilayers. Each of the layers is in a star-of-David (SOD) charge-density-wave phase. Geometric and electronic structures and magnetic properties of 28 different stacking configurations are examined and analyzed using density-functional-theory calculations. It is found that the SOD contains a localized region, in which interlayer Se p_z hybridization plays a paramount role in varying the energy levels of the two Hubbard bands. These variations lead to three electronic transitions among four insulating states, which demonstrate the effectiveness of interlayer interactions to modulate correlated magnetic properties in a prototypical correlated magnetic insulator.     

Ferroelectric Control of Polarity of the Spin-polarized Current in Van Der Waals Multiferroic Heterostructures

Ferroelectric (FE) control of magnetism at nanoscale, for instance, FE control of the polarity of spin-polarized current is crucial for technological advances in magnetoelectric and spintronic applications. However, this fascinating functionality has not been reported in nanoscale systems yet. Herein, a new class of FE/A-type antiferromagnetic heterobilayer/FE van der Waals (vdW) multiferroic structures is found, in which the FE control of polarity of spin-polarized current is found possible. Take Sc₂CO₂/CrSiTe₃/CrGeTe₃/Sc₂CO₂ heterostructure as a successful example. First-principles calculations reveal that its polarity of half-metallicity can be switched by flipping the FE polarization orientation. Meanwhile, device transport simulation shows that its up/down spin current transmission ratio is as large as 0.1 × 10³ at $\overrightarrow{\mathrm{P}}\uparrow \uparrow$ Sc₂CO₂ configuration and is only 2.6 × 10⁻³ at $\overrightarrow{\mathrm{P}}\downarrow \downarrow$ Sc₂CO₂ configuration in the vdW multiferroic heterostructures. Essentially, it stems from the reversible FE switch of the internal electric field across the CrSiTe₃/CrGeTe₃ heterobilayer and the FE control of the interfacial effect between Sc₂CO₂ and Cr(Si/Ge)Te₃ layers. This work opens a direction for constructing low-energy-dissipation, non-volatile, and high-sensitive spintronic devices such as spin field-effect transistors.     

Strain Anisotropy Driven Spontaneous Formation of Nanoscrolls from 2D Janus Layers

2D Janus transition metal dichalcogenides (TMDs) have attracted attention due to their emergent properties arising from broken mirror symmetry and self-driven polarization fields. While it has been proposed that their vdW superlattices hold the key to achieving superior properties in piezoelectricity and photovoltaic, available synthesis has ultimately limited their realization. Here, the first packed vdW nanoscrolls made from Janus TMDs through a simple one-drop solution technique are reported. The results, including ab initio simulations, show that the Bohr radius difference between the top sulfur and the bottom selenium atoms within Janus ${\mathrm{M}}_{\mathrm{Se}}^{\mathrm{S}}$ (M = Mo, W) results in a permanent compressive surface strain that acts as a nanoscroll formation catalyst after small liquid interaction. Unlike classical 2D layers, the surface strain in Janus TMDs can be engineered from compressive to tensile by placing larger Bohr radius atoms on top (${\mathrm{M}}_{\mathrm{S}}^{\mathrm{Se}})$to yield inverted C scrolls. Detailed microscopy studies offer the first insights into their morphology and readily formed Moiré lattices. In contrast, spectroscopy and FETs studies establish their excitonic and device properties and highlight significant differences compared to 2D flat Janus TMDs. These results introduce the first polar Janus TMD nanoscrolls and introduce inherent strain-driven scrolling dynamics as a catalyst to create superlattices.     

Giant Electric Field-Induced Strain with High Temperature-Stability in Textured KNN-Based Piezoceramics for Actuator Applications

Large-strain (K,Na)NbO₃ (KNN) based piezoceramics are attractive for next-generation actuators because of growing environmental concerns. However, inferior performance with poor temperature stability greatly hinders their industrialized procedure. Herein, a feasible strategy is proposed by introducing ${\mathrm{V}}_{\text{K/Na}}^{{}^{\prime }}$-${\mathrm{V}}_{\stackrel{\mathrm{..}}{\mathrm{O}}}$ defect dipoles and constructing grain orientation to enhance the strain performance and temperature stability of KNN-based piezoceramics. This textured ceramics with 90.3% texture degree exhibit a giant strain (1.35%) and a large converse piezoelectric coefficient d₃₃^* (2700 pm V⁻¹), outperforming most lead-free piezoceramics and even some single crystals. Meanwhile, the strain deviation at high temperature of 100 °C–200 °C is obviously alleviated from 61% to 35% through texture engineering. From the perspective of practical applications, piezo-actuators are commonly utilized in the form of multilayer. In order to illustrate the applicability on multilayer actuators, a stack-type actuator consisted of 5 layers of 0.4 mm thick ceramics is fabricated. It can generate large field-induced displacement (11.6 µm), and the promising potential in precise positioning and optical modulation are further demonstrated. This work provides a textured KNN-based piezoceramic with temperature-stable giant strain properties, and facilitates the lead-free piezoceramic materials in actuator applications.     

Promoting “Strong Adsorption” and “Fast Conversion” of Polysulfides in Li-S batteries Based on Conductive Sulfides Host with Hollow Prism Structure and Surface Defects

The chemical binding between metal compounds and polysulfides provides a good solution to inhibit shuttle effect in Li-S batteries. However, the Sabatier principle predicts that overly strong adsorption will commonly hinder the conversion of polysulfides, so building the synergetic effect mechanism between “strong adsorption” and “fast conversion” for polysulfides is a significant strategy. To realize this goal, in this study, the defect-enriched Co₉S₈ hollow prisms (DHCPs) as both S host and catalyst material for Li-S batteries are designed. Based on in situ UV–vis spectroscopy results, it is found that DHCPs can profitably promote the generation of ${\mathrm{S}}_3^{·-}$ radicals during the discharge process. In the case of the relatively high conversion barrier of “liquid–liquid” reaction, the generated ${\mathrm{S}}_3^{·-}$ radicals are responsible for the fast conversion reaction via a unique reaction pathway. When the sulfur loading is 4.63 mg cm⁻², the cell with DHCP/S cathode delivers a high areal capacity of 4.75 mAh cm⁻² at 0.1 C and keeps a high capacity of 2.99 mAh cm⁻² after 100 cycles at 0.5 C. This study provides a positive attempt to achieve “strong adsorption” and “fast conversion” of polysulfides simultaneously, which will convincingly boost the development and practical process of Li-S batteries.     

Anisotropic Phonon Response of Few‐Layer PdSe2 under Uniaxial Strain

PdSe₂, an emerging 2D material with a novel anisotropic puckered pentagonal structure, has attracted growing interest due to its layer‐dependent electronic bandgap, high carrier mobility, and good air stability. Herein, a detailed Raman spectroscopic study of few‐layer PdSe₂ (two to five layers) under the in‐plane uniaxial tensile strain up to 3.33% is performed. Two of the prominent PdSe₂ Raman peaks are influenced differently depending on the direction of strain application. The $A_g^1$ mode redshifts more than the $A_g^3$ mode when the strain is applied along the a‐axis of the crystal, while the $A_g^3$ mode redshifts more than the $A_g^1$ mode when the strain is applied along the b‐axis. Such an anisotropic phonon response to strain indicates directionally dependent mechanical and thermal properties of PdSe₂ and also allows the identification of the crystal axes. The results are further supported using first‐principles density‐functional theory. Interestingly, the near‐zero Poisson’s ratios for few‐layer PdSe₂ are found, suggesting that the uniaxial tensile strain can easily be applied to few‐layer PdSe₂ without significantly altering their dimensions at the perpendicular directions, which is a major contributing factor to the observed distinct phonon behavior. The findings pave the way for further development of 2D PdSe₂‐based flexible electronics.