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We proposed a dual-channel narrow band filter consisting of top and bottom-distributed Bragg reflectors (DBRs) and a dielectric interlayer inserted with a metasurface. Through the design of the metasurface, the two channels of the filter are guaranteed to exhibit high-quality factors with transmittance beyond 90% and full width at half maximum (FWHM) less than 10 nm. We demonstrate that the central wavelengths of each dual-channel filter can be controlled with a total of 50 nm shifts by only changing the width of the metasurface. Compared with the traditional dual-channel filter, our design is easier to fabricate and more convenient to tune the central wavelength, which is promising for ultracompact optical devices.

Controlling the crystal structure is a powerful approach for manipulating the fundamental properties of solids. In van der Waals materials, this control can be achieved by modifying the stacking order through rotation and translation between the layers. Here, we observed stacking-dependent interlayer magnetism in the two-dimensional (2D) magnetic semiconductor chromium tribromide (CrBr3), which was enabled by the successful growth of its monolayer and bilayer through molecular beam epitaxy. Using in situ spin-polarized scanning tunneling microscopy and spectroscopy, we directly correlate the atomic lattice structure with the observed magnetic order. Although the individual monolayer CrBr3 is ferromagnetic, the interlayer coupling in bilayer depends on the stacking order and can be either ferromagnetic or antiferromagnetic. Our observations pave the way for manipulating 2D magnetism with layer twist angle control.

Conductive Ti3C2Tx MXenes have been widely investigated for the construction of flexible and highly‐sensitive pressure sensors. Although the inevitable oxidation of solution‐processed MXene has been recognized, the effect of the irreversible oxidation of MXene on its electrical conductivity and sensing properties is yet to be understood. Herein, we construct a highly‐sensitive and degradable piezoresistive pressure sensor by coating Ti3C2Tx MXene flakes with different degrees of in situ oxidation onto paper substrates using the dipping‐drying method. In situ oxidation can tune the intrinsic resistance and expand the interlayer distance of MXene nanosheets. The partially oxidized MXene‐based piezoresistive pressure sensor exhibits a high sensitivity of 28.43 kPa−1, which is greater than those of pristine MXene, over‐oxidized MXene, and state‐of‐the‐art paper‐based pressure sensors. Additionally, these sensors exhibit a short response time of 98.3 ms, good durability over 5000 measurement cycles, and a low force detection limit of 0.8 Pa. Moreover, MXene‐based sensing elements are easily degraded and environmentally friendly. The MXene‐based pressure sensor shows promise for practical applications in tracking body movements, sports coaching, remote health monitoring, and human–computer interactions. The highly‐sensitive and degradable piezoresistive pressure sensor was constructed by coating Ti3C2Tx MXene flakes with different degrees of in situ oxidation onto paper substrates using the dipping‐drying method. In situ oxidation tunes the intrinsic resistance and expand the interlayer distance of MXene nanosheets, which regulates the sensitivity of the sensor. It is found that the partially oxidized MXene based pressure sensor demonstrates remarkably higher sensitivity (28.43 kPa−1) than those of pristine MXene, over‐oxidized MXene, and state‐of‐the‐art paper‐based pressure sensors.

Hybrid perovskite solar cells often use the more thermally stable formamidinium (FA) cation rather than methylammonium, but its larger size can create lattice distortion that results in an inactive yellow phase. Turren-Cruz et al. show that by using iodide instead of bromide as the anion (to create a redder bandgap) and an optical mix of cesium, rubidium, and FA cations, they can make solar cells with a stabilized efficiency of more than 20%. No heating steps above 100°C were needed to create the preferred black phase. Science , this issue p. 449 Avoidance of bromide anions and methylammonium cations allows optimal tuning of perovskite bandgaps. Currently, perovskite solar cells (PSCs) with high performances greater than 20% contain bromine (Br), causing a suboptimal bandgap, and the thermally unstable methylammonium (MA) molecule. Avoiding Br and especially MA can therefore result in more optimal bandgaps and stable perovskites. We show that inorganic cation tuning, using rubidium and cesium, enables highly crystalline formamidinium-based perovskites without Br or MA. On a conventional, planar device architecture, using polymeric interlayers at the electron- and hole-transporting interface, we demonstrate an efficiency of 20.35% (stabilized), one of the highest for MA-free perovskites, with a drastically improved stability reached without the stabilizing influence of mesoporous interlayers. The perovskite is not heated beyond 100°C. Going MA-free is a new direction for perovskites that are inherently stable and compatible with tandems or flexible substrates, which are the main routes commercializing PSCs.

An electrical current running through two stacked magnetic layers is larger if their magnetizations point in the same direction than if they point in opposite directions. These so-called magnetic tunnel junctions, used in electronics, must be carefully engineered. Two groups now show that high magnetoresistance intrinsically occurs in samples of the layered material CrI 3 sandwiched between graphite contacts. By varying the number of layers in the samples, Klein et al. and Song et al. found that the electrical current running perpendicular to the layers was largest in high magnetic fields and smallest near zero field. This observation is consistent with adjacent layers naturally having opposite magnetizations, which align parallel to each other in high magnetic fields. Science , this issue p. 1218 , p. 1214 The atomic layers of the material CrI 3 act as spin filters in graphite/CrI 3 /graphite junctions. Magnetic insulators are a key resource for next-generation spintronic and topological devices. The family of layered metal halides promises varied magnetic states, including ultrathin insulating multiferroics, spin liquids, and ferromagnets, but device-oriented characterization methods are needed to unlock their potential. Here, we report tunneling through the layered magnetic insulator CrI 3 as a function of temperature and applied magnetic field. We electrically detect the magnetic ground state and interlayer coupling and observe a field-induced metamagnetic transition. The metamagnetic transition results in magnetoresistances of 95, 300, and 550% for bilayer, trilayer, and tetralayer CrI 3 barriers, respectively. We further measure inelastic tunneling spectra for our junctions, unveiling a rich spectrum consistent with collective magnetic excitations (magnons) in CrI 3 .

A van der Waals heterostructure built from atomically thin semiconducting transition metal dichalcogenides (TMDs) enables the formation of excitons from electrons and holes in distinct layers, producing interlayer excitons with large binding energy and a long lifetime. By employing heterostructures of monolayer TMDs, we realize optical and electrical generation of long-lived neutral and charged interlayer excitons. We demonstrate that neutral interlayer excitons can propagate across the entire sample and that their propagation can be controlled by excitation power and gate electrodes. We also use devices with ohmic contacts to facilitate the drift motion of charged interlayer excitons. The electrical generation and control of excitons provide a route for achieving quantum manipulation of bosonic composite particles with complete electrical tunability.

In perovskite solar cells, the interfaces between the perovskite and charge-transporting layers contain high concentrations of defects (about 100 times that within the perovskite layer), specifically, deep-level defects, which substantially reduce the power conversion efficiency of the devices 1 – 3 . Recent efforts to reduce these interfacial defects have focused mainly on surface passivation 4 – 6 . However, passivating the perovskite surface that interfaces with the electron-transporting layer is difficult, because the surface-treatment agents on the electron-transporting layer may dissolve while coating the perovskite thin film. Alternatively, interfacial defects may not be a concern if a coherent interface could be formed between the electron-transporting and perovskite layers. Here we report the formation of an interlayer between a SnO 2 electron-transporting layer and a halide perovskite light-absorbing layer, achieved by coupling Cl-bonded SnO 2 with a Cl-containing perovskite precursor. This interlayer has atomically coherent features, which enhance charge extraction and transport from the perovskite layer, and fewer interfacial defects. The existence of such a coherent interlayer allowed us to fabricate perovskite solar cells with a power conversion efficiency of 25.8 per cent (certified 25.5 per cent)under standard illumination. Furthermore, unencapsulated devices maintained about 90 per cent of their initial efficiency even after continuous light exposure for 500 hours. Our findings provide guidelines for designing defect-minimizing interfaces between metal halide perovskites and electron-transporting layers. An atomically coherent interlayer between the electron-transporting and perovskite layers in perovskite solar cells enhances charge extraction and transport from the perovskite, enabling high power conversion efficiency.

The shuttle effect of soluble lithium polysulfides during the charge/discharge process is the key bottleneck hindering the practical application of lithium–sulfur batteries. Herein, a multifunctional interlayer is developed by growing metallic molybdenum disulfide nanosheets on both outer and inner walls of cotton cloth derived carbon microtube textile (MoS2@CMT). The hollow structure of CMT provides channels to favor electrolyte penetration, Li+ diffusion and restrains polysulfides via physical confinement. The hydrophilic and conductive 1T‐MoS2 nanosheets facilitate chemisorption and kinetic behavior of polysulfides. The synergic effect of 1T‐MoS2 nanosheets and CMT affords the MoS2@CMT interlayer with an efficient trapping‐diffusion‐conversion ability toward polysulfides. Therefore, the cell with the MoS2@CMT interlayer exhibits enhanced cycling life (765 mAh g−1 after 500 cycles at 0.5 C) and rate performance (974 mAh g−1 at 2 C and 740 mAh g−1 at 5 C). This study presents a pathway to develop low‐cost multifunctional interlayers for advanced lithium–sulfur batteries. MoS2 nanosheets grown on both outer and inner walls of carbon microtube textile (MoS2@CMT) are designed as the interlayer for lithium–sulfur batteries. The synergic effect of MoS2 nanosheets and CMT can effectively enhance the diffusion of Li+, anchor and catalyze the conversion of lithium polysulfides to Li2S2/Li2S.

In heterostructures assembled from two-dimensional materials such as graphene, electron tunneling between layers varies strongly with the rotation angle between the crystal lattices. Usually, the twist angle between layers is fixed after assembly. Ribeiro-Palau et al. encapsulated graphene with boron nitride, but the top boron nitride flake was shaped so that an atomic force microscope tip could push on it to vary the twist angle by as little as 0.2°. They observed variations with twist angle in properties such as the charge neutrality point, which would be difficult to observe in static rotated structures. Science , this issue p. 690 An atomic force microscope tip is used to control the relative angle between graphene and boron nitride layers. In heterostructures of two-dimensional materials, electronic properties can vary dramatically with relative interlayer angle. This effect makes it theoretically possible to realize a new class of twistable electronics in which properties can be manipulated on demand by means of rotation. We demonstrate a device architecture in which a layered heterostructure can be dynamically twisted in situ. We study graphene encapsulated by boron nitride, where, at small rotation angles, the device characteristics are dominated by coupling to a long-wavelength moiré superlattice. The ability to investigate arbitrary rotation angle in a single device reveals features of the optical, mechanical, and electronic response in this system not captured in static rotation studies. Our results establish the capability to fabricate twistable electronic devices with dynamically tunable properties.

Graphene is an atomically thin material that supports highly confined plasmon polaritons, or nano-light, with very low loss. The properties of graphene can be made richer by introducing and then rotating a second layer so that there is a slight angle between the atomic registry. Sunku et al. show that the moiré patterns that result from such twisted bilayer graphene also provide confined conducting channels that can be used for the directed propagation of surface plasmons. Controlling the structure thereby provides a pathway to control and route surface plasmons for a nanophotonic platform. Science , this issue p. 1153 Twisted bilayer graphene hosts periodic arrays of conducting channels for the directed propagation of surface plasmons. Graphene is an atomically thin plasmonic medium that supports highly confined plasmon polaritons, or nano-light, with very low loss. Electronic properties of graphene can be drastically altered when it is laid upon another graphene layer, resulting in a moiré superlattice. The relative twist angle between the two layers is a key tuning parameter of the interlayer coupling in thus-obtained twisted bilayer graphene (TBG). We studied the propagation of plasmon polaritons in TBG by infrared nano-imaging. We discovered that the atomic reconstruction occurring at small twist angles transforms the TBG into a natural plasmon photonic crystal for propagating nano-light. This discovery points to a pathway for controlling nano-light by exploiting quantum properties of graphene and other atomically layered van der Waals materials, eliminating the need for arduous top-down nanofabrication.