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Gold-based co-catalysts are a promising class of materials with potential applications in photocatalytic H 2 O 2 production. However, current approaches with Au co-catalysts show limited H 2 O 2 production due to intrinsically weak O 2 adsorption at the Au site. We report an approach to strengthen O 2 adsorption at Au sites, and to improve H 2 O 2 production, through the formation of electron-deficient Au δ+ sites by modifying the electronic structure. In this case, we report the synthesis of TiO 2 /MoS x -Au, following selective deposition of Au onto a MoS x surface which is then further anchored onto TiO 2 . We further show that the catalyst achieves a significantly increased H 2 O 2 production rate of 30.44 mmol g −1  h −1 in O 2 -saturated solution containing ethanol. Density functional theory calculations and X-ray photoelectron spectroscopy analysis reveal that the MoS x mediator induces the formation of electron-deficient Au δ+ sites thereby decreasing the antibonding-orbital occupancy of Au-O ads and subsequently enhancing O 2 adsorption. This strategy may be useful for rationally designing the electronic structure of catalyst surfaces to facilitate artificial photosynthesis. Photocatalytic H 2 O 2 production using Au is hindered by its inherently weak O 2 adsorption. Herein, the authors modify the electronic structure of Au with MoS x to form electron deficient Au sites to promote O 2 adsorption and H 2 O 2 production.

Electrocatalytic recycling of waste nitrate (NO 3 − ) to valuable ammonia (NH 3 ) at ambient conditions is a green and appealing alternative to the Haber−Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate NH 3 synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade NO 3 − -to-NH 3 conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu−Co binary sulfides into potential-dependent core−shell Cu/CuO x and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in−situ Raman spectra reveal that the inner Cu/CuO x phases preferentially catalyze NO 3 − reduction to NO 2 − , which is rapidly reduced to NH 3 at the nearby Co/CoO shell. This unique tandem catalyst system leads to a NO 3 − -to-NH 3 Faradaic efficiency of 93.3 ± 2.1% in a wide range of NO 3 − concentrations at pH 13, a high NH 3 yield rate of 1.17 mmol cm −2 h −1 in 0.1 M NO 3 − at −0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports. Electrocatalytic recycling of waste nitrate to NH 3 under ambient conditions maybe an appealing alternative to the Haber−Bosch process. Here the authors report a tandem catalyst system involving cooperative adsorption of reaction intermediate on different transition metal active sites for nitrate electroreduction with high efficiency.

The Mott insulator is a central concept in strongly correlated physics and manifests when the repulsive Coulomb interaction between electrons dominates over their kinetic energy1,2. Doping additional carriers into a Mott insulator can give rise to other correlated phenomena such as unusual magnetism and even high-temperature superconductivity2,3. A tunable Mott insulator, where the competition between the Coulomb interaction and the kinetic energy can be varied in situ, can provide an invaluable model system for the study of Mott physics. Here we report the possible realization of such a tunable Mott insulator in a trilayer graphene heterostructure with a moiré superlattice. The combination of the cubic energy dispersion in ABC-stacked trilayer graphene4–8 and the narrow electronic minibands induced by the moiré potential9–15 leads to the observation of insulating states at the predicted band fillings for the Mott insulator. Moreover, the insulating states in the heterostructure can be tuned: the bandgap can be modulated by a vertical electrical field, and at the same time the electron doping can be modified by a gate to fill the band from one insulating state to another. This opens up exciting opportunities to explore strongly correlated phenomena in two-dimensional moiré superlattice heterostructures.Report of the likely observation of a Mott insulator in trilayer graphene with a moiré potential. The Mott state can be tuned between different filling fractions via gating, which will enable the careful study of this paradigmatic many-body state.

Solution-processed planar perovskite devices are highly desirable in a wide variety of optoelectronic applications; however, they are prone to hysteresis and current instabilities. Here we report the first perovskite–PCBM hybrid solid with significantly reduced hysteresis and recombination loss achieved in a single step. This new material displays an efficient electrically coupled microstructure: PCBM is homogeneously distributed throughout the film at perovskite grain boundaries. The PCBM passivates the key PbI 3 − antisite defects during the perovskite self-assembly, as revealed by theory and experiment. Photoluminescence transient spectroscopy proves that the PCBM phase promotes electron extraction. We showcase this mixed material in planar solar cells that feature low hysteresis and enhanced photovoltage. Using conductive AFM studies, we reveal the memristive properties of perovskite films. We close by positing that PCBM, by tying up both halide-rich antisites and unincorporated halides, reduces electric field-induced anion migration that may give rise to hysteresis and unstable diode behaviour. Metal halide perovskites are promising for solar energy harvesting, but currently prone to a large hysteresis and current instability. Here, Xu et al . show improvements in a hybrid material in which the fullerene is distributed at perovskite grain boundaries and thus passivates defects effectively.

Long-wavelength near-infrared light-emitting diodes (NIR LEDs) with peak emission wavelengths beyond 900 nm are of critical importance for various applications including night vision, biomedical imaging, sensing and optical communications. However, the low radiance and poor operational stability of state-of-the-art long-wavelength NIR LEDs based on soft materials remain the most critical factors limiting their practical applications. Here we develop NIR LEDs emitting beyond 900 nm with improved performance through the rational manipulation of p doping in all-inorganic tin perovskites (CsSnI 3 ) by retarding and controlling the crystallization process of perovskite precursors in tin-rich conditions. The resulting NIR LEDs exhibit a peak emission wavelength at 948 nm, high radiance of 226 W sr −1  m −2 and long operational half-lifetime of 39.5 h at a high constant current density of 100 mA cm −2 . Our demonstration of efficient and stable NIR LEDs operating at high current densities may also open up new opportunities towards electrically pumped lasers. Controlling the intrinsic doping of lead-free perovskites enables near-infrared LEDs emitting at 948 nm with a peak radiance of 226 W sr –1  m –2 and a half-lifetime of 39.5 h.

Lithium niobate (LiNbO 3 ) is viewed as a promising material for optical communications and quantum photonic chips 1 , 2 . Recent breakthroughs in LiNbO 3 nanophotonics have considerably boosted the development of high-speed electro-optic modulators 3 – 5 , frequency combs 6 , 7 and broadband spectrometers 8 . However, the traditional method of electrical poling for ferroelectric domain engineering in optic 9 – 13 , acoustic 14 – 17 and electronic applications 18 , 19 is limited to two-dimensional space and micrometre-scale resolution. Here we demonstrate a non-reciprocal near-infrared laser-writing technique for reconfigurable three-dimensional ferroelectric domain engineering in LiNbO 3 with nanoscale resolution. The proposed method is based on a laser-induced electric field that can either write or erase domain structures in the crystal, depending on the laser-writing direction. This approach offers a pathway for controllable nanoscale domain engineering in LiNbO 3 and other transparent ferroelectric crystals, which has potential applications in high-efficiency frequency mixing 20 , 21 , high-frequency acoustic resonators 14 – 17 and high-capacity non-volatile ferroelectric memory 19 , 22 . We propose and experimentally demonstrate a non-reciprocal near-infrared femtosecond laser-writing technique for reconfigurable three-dimensional nanoscale ferroelectric domain engineering in LiNbO 3 crystals.

The quantum-level interplay between geometry, topology and correlation is at the forefront of fundamental physics 1 – 15 . Kagome magnets are predicted to support intrinsic Chern quantum phases owing to their unusual lattice geometry and breaking of time-reversal symmetry 14 , 15 . However, quantum materials hosting ideal spin–orbit-coupled kagome lattices with strong out-of-plane magnetization are lacking 16 – 21 . Here, using scanning tunnelling microscopy, we identify a new topological kagome magnet, TbMn 6 Sn 6 , that is close to satisfying these criteria. We visualize its effectively defect-free, purely manganese-based ferromagnetic kagome lattice with atomic resolution. Remarkably, its electronic state shows distinct Landau quantization on application of a magnetic field, and the quantized Landau fan structure features spin-polarized Dirac dispersion with a large Chern gap. We further demonstrate the bulk–boundary correspondence between the Chern gap and the topological edge state, as well as the Berry curvature field correspondence of Chern gapped Dirac fermions. Our results point to the realization of a quantum-limit Chern phase in TbMn 6 Sn 6 , and may enable the observation of topological quantum phenomena in the RMn 6 Sn 6 (where R is a rare earth element) family with a variety of magnetic structures. Our visualization of the magnetic bulk–boundary–Berry correspondence covering real space and momentum space demonstrates a proof-of-principle method for revealing topological magnets. Scanning tunnelling microscopy is used to reveal a new topological kagome magnet with an intrinsic Chern quantum phase, which shows a distinct Landau fan structure with a large Chern gap.

The two natural allotropes of carbon, diamond and graphite, are extended networks of sp 3 -hybridized and sp 2 -hybridized atoms, respectively 1 . By mixing different hybridizations and geometries of carbon, one could conceptually construct countless synthetic allotropes. Here we introduce graphullerene, a two-dimensional crystalline polymer of C 60 that bridges the gulf between molecular and extended carbon materials. Its constituent fullerene subunits arrange hexagonally in a covalently interconnected molecular sheet. We report charge-neutral, purely carbon-based macroscopic crystals that are large enough to be mechanically exfoliated to produce molecularly thin flakes with clean interfaces—a critical requirement for the creation of heterostructures and optoelectronic devices 2 . The synthesis entails growing single crystals of layered polymeric (Mg 4 C 60 ) ∞ by chemical vapour transport and subsequently removing the magnesium with dilute acid. We explore the thermal conductivity of this material and find it to be much higher than that of molecular C 60 , which is a consequence of the in-plane covalent bonding. Furthermore, imaging few-layer graphullerene flakes using transmission electron microscopy and near-field nano-photoluminescence spectroscopy reveals the existence of moiré-like superlattices 3 . More broadly, the synthesis of extended carbon structures by polymerization of molecular precursors charts a clear path to the systematic design of materials for the construction of two-dimensional heterostructures with tunable optoelectronic properties. A two-dimensional crystalline polymer of C 60 , termed graphullerene, is synthesized by chemical vapour transport, and mechanically exfoliated to produce molecularly thin flakes with clean interfaces for potential optoelectronic applications.

The discovery of materials has often introduced new physical paradigms and enabled the development of novel devices. Two-dimensional magnetism, which is associated with strong intrinsic spin fluctuations, has long been the focus of fundamental questions in condensed matter physics regarding our understanding and control of new phases. Here we discuss magnetic van der Waals materials: two-dimensional atomic crystals that contain magnetic elements and thus exhibit intrinsic magnetic properties. These cleavable materials provide the ideal platform for exploring magnetism in the two-dimensional limit, where new physical phenomena are expected, and represent a substantial shift in our ability to control and investigate nanoscale phases. We present the theoretical background and motivation for investigating this class of crystals, describe the material landscape and the current experimental status of measurement techniques as well as devices, and discuss promising future directions for the study of magnetic van der Waals materials. Recent advances and future directions for the research of magnetic two-dimensional van der Waals materials are reviewed.

Ultrathin ferroelectric materials could potentially enable low-power logic and nonvolatile memories 1 , 2 . As ferroelectric materials are made thinner, however, the ferroelectricity is usually suppressed. Size effects in ferroelectrics have been thoroughly investigated in perovskite oxides—the archetypal ferroelectric system 3 . Perovskites, however, have so far proved unsuitable for thickness scaling and integration with modern semiconductor processes 4 . Here we report ferroelectricity in ultrathin doped hafnium oxide (HfO 2 ), a fluorite-structure oxide grown by atomic layer deposition on silicon. We demonstrate the persistence of inversion symmetry breaking and spontaneous, switchable polarization down to a thickness of one nanometre. Our results indicate not only the absence of a ferroelectric critical thickness but also enhanced polar distortions as film thickness is reduced, unlike in perovskite ferroelectrics. This approach to enhancing ferroelectricity in ultrathin layers could provide a route towards polarization-driven memories and ferroelectric-based advanced transistors. This work shifts the search for the fundamental limits of ferroelectricity to simpler transition-metal oxide systems—that is, from perovskite-derived complex oxides to fluorite-structure binary oxides—in which ‘reverse’ size effects counterintuitively stabilize polar symmetry in the ultrathin regime. Enhanced switchable ferroelectric polarization is achieved in doped hafnium oxide films grown directly onto silicon using low-temperature atomic layer deposition, even at thicknesses of just one nanometre.