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The electrochemical formation of liquid sulfur at room temperature on the basal plane of MoS

Deciphering the atomic and electronic structures of interfaces is key to developing state-of-the-art perovskite semiconductors. However, conventional characterization techniques have limited previous studies mainly to grain-boundary interfaces, whereas the intragrain-interface microstructures and their electronic properties have been much less revealed. Herein using scanning transmission electron microscopy, we resolved the atomic-scale structural information on three prototypical intragrain interfaces, unraveling intriguing features clearly different from those from previous observations based on standalone films or nanomaterial samples. These intragrain interfaces include composition boundaries formed by heterogeneous ion distribution, stacking faults resulted from wrongly stacked crystal planes, and symmetrical twinning boundaries. The atomic-scale imaging of these intragrain interfaces enables us to build unequivocal models for the ab initio calculation of electronic properties. Our results suggest that these structure interfaces are generally electronically benign, whereas their dynamic interaction with point defects can still evoke detrimental effects. This work paves the way toward a more complete fundamental understanding of the microscopic structure–property–performance relationship in metal halide perovskites.

High-quality air-stable ultrathin crystalline Fe3O4 nanosheets, van der Waals epitaxially grown on mica, exhibit high-temperature ferrimagnetic behavior with a TC of 847 K and a large and saturated anomalous Hall effect at room temperature.

The fundamental understanding and rational regulation of effective metal–sulfur conversion reactions in metal–sulfur batteries.

Phase transitions in two-dimensional (2D) materials promise reversible modulation of material physical and chemical properties in a wide range of applications. 2D van der Waals layered In 2 Se 3 with bistable out-of-plane ferroelectric (FE) α phase and antiferroelectric (AFE) β′ phase is particularly attractive for its electronic applications. However, reversible phase transition in 2D In 2 Se 3 remains challenging. Here, we introduce two factors, dimension (thickness) and strain, which can effectively modulate the phases of 2D In 2 Se 3 . We achieve reversible AFE and out-of-plane FE phase transition in 2D In 2 Se 3 by delicate strain control inside a transmission electron microscope. In addition, the polarizations in 2D FE In 2 Se 3 can also be manipulated in situ at the nanometer-sized contacts, rendering remarkable memristive behavior. Our in situ transmission electron microscopy (TEM) work paves a previously unidentified way for manipulating the correlated FE phases and highlights the great potentials of 2D ferroelectrics for nanoelectromechanical and memory device applications.

2D hybrid perovskites with strong spin–orbit coupling (SOC) and structural asymmetry represent a new class of quantum materials that can potentially display coexisting ferroelectricity and Rashba spin splitting. Studies on these systems provide insight into the coupling between strain, spin, and electronic degrees of freedom, as well as symmetry and order parameters in the bulk and at the interfaces. We review design principles for ferroelectric hybrid perovskites with tunable band gaps, Rashba spin-split properties, and multiple polar axes. Different from traditional inorganic semiconductors, the composition and chirality of the organic cation, along with the strength of the coupling between the organic and inorganic components, play key roles in deciding the structural asymmetry that drives ferroelectricity and the spin orbit field.

Large‐scale production of two‐dimensional (2D) materials still is a crucial point toward its practical applications. Violet phosphorus (VP) with a wide bandgap accelerates and broadens the potential applications of elemental phosphorus in optoelectronics. Here, we demonstrate the scalable production of solution‐processable violet phosphorus flakes stably dispersed in several solvents. The exfoliated VP flakes exhibit thickness‐dependent visible photoluminescence characteristics, which covers the shortcoming of black phosphorus. Meanwhile, the VP‐based field‐effect transistor reveals relatively competitive electrical properties to other liquid‐phase exfoliated 2D materials. Our study paves the way for a wide range of applications of optical devices, energy storage, catalysis, and sodium batteries based on large‐scale VP flakes.

X-ray detectors need to be operated at as low as possible doses to reduce radiation health risks during x-ray security examination or medical inspection, which drives the efforts to explore novel detectors with high sensitivity and low detection limits. Organolead trihalide perovskite is the champion, with the highest sensitivity and lowest detection limit. Unfortunately, these materials threaten the safety of the human body and environment by the toxic issue of lead. Here we present a new environmentally friendly material with van der Waals heterostructure of BixIy for ultra-sensitive x-ray detection. The BixIy detector provides anisotropic x-ray detecting performance with a sensitivity up to 1.3×105 µC Gy− 1 cm− 2 and a detection limit as low as 34 nGy s− 1. Meanwhile, our BixIy detector demonstrates wonderful environmental and hard radiation stabilities. Our discovery inspires the search for new van der Waals heterostructure classes to realize high-performance x-ray detectors and other optoelectronic devices without employing toxic elements.

Two-dimensional materials provide opportunities for developing semiconductor applications at atomistic thickness to break the limits of silicon technology. Black phosphorus (BP), as a layered semiconductor with controllable bandgap and high carrier mobility, is one of the most promising candidates for transistor devices at atomistic thickness1–4. However, the lack of large-scale growth greatly hinders its development in devices. Here, we report the growth of ultrathin BP on the centimetre scale through pulsed laser deposition. The unique plasma-activated region induced by laser ablation provides highly desirable conditions for BP cluster formation and transportation5,6, facilitating growth. Furthermore, we fabricated large-scale field-effect transistor arrays on BP films, yielding appealing hole mobility of up to 213 and 617 cm2 V−1 s−1 at 295 and 250 K, respectively. Our results pave the way for further developing BP-based wafer-scale devices with potential applications in the information industry. Centimetre-scale growth of few-layer black phosphorous with high crystalline quality and homogeneity is realized by pulsed laser deposition.

Two-dimensional materials with out-of-plane (OOP) ferroelectric and piezoelectric properties are highly desirable for the realization of ultrathin ferro- and piezoelectronic devices. We demonstrate unexpected OOP ferroelectricity and piezoelectricity in untwisted, commensurate, and epitaxial MoS 2 /WS 2 heterobilayers synthesized by scalable one-step chemical vapor deposition. We show d 33 piezoelectric constants of 1.95 to 2.09 picometers per volt that are larger than the natural OOP piezoelectric constant of monolayer In 2 Se 3 by a factor of ~6. We demonstrate the modulation of tunneling current by about three orders of magnitude in ferroelectric tunnel junction devices by changing the polarization state of MoS 2 /WS 2 heterobilayers. Our results are consistent with density functional theory, which shows that both symmetry breaking and interlayer sliding give rise to the unexpected properties without the need for invoking twist angles or moiré domains.

Four interrelated issues have been arising with the development of modern industry, namely environmental pollution, the energy crisis, the greenhouse effect and the global food crisis. Photocatalysis is one of the most promising methods to solve them in the future. To promote high photocatalytic reaction efficiency and utilize solar energy to its fullest, a well-designed photoreactor is vital. Photocatalytic optofluidic microreactors, a promising technology that brings the merits of microfluidics to photocatalysis, offer the advantages of a large surface-to-volume ratio, a short molecular diffusion length and high reaction efficiency, providing a potential method for mitigating the aforementioned crises in the future. Although various photocatalytic optofluidic microreactors have been reported, a comprehensive review of microreactors applied to these four fields is still lacking. In this paper, we review the typical design and development of photocatalytic microreactors in the fields of water purification, water splitting, CO2 fixation and coenzyme regeneration in the past few years. As the most promising tool for solar energy utilization, we believe that the increasing innovation of photocatalytic optofluidic microreactors will drive rapid development of related fields in the future.

Lieb lattice, a two-dimensional edge-centered square lattice, has attracted considerable interest due to its exotic electronic and topological properties. Although various optical and photonic Lieb lattices have been experimentally demonstrated, it remains challenging for an electronic Lieb lattice to be realized in real material systems. Here, based on first-principles calculations and tight-binding modeling, a silver sulfide (Ag2S) monolayer is reported as a long-sought-after inorganic electronic Lieb lattice. This Lieb-lattice Ag2S is further found to be ultrasoft, which enables its electronic properties and topological states near the Fermi level to be finely tuned, as evidenced by the strain-induced topologically non-trivial edge states near the valence band edge. These results not only provide an ideal platform to further explore and harvest interesting quantum properties but also pave a way to pursue other inorganic electronic Lieb lattices in a broader material domain.

Metal halide perovskites are emerging materials for next-generation optoelectronic devices, of which the all-inorganic CsPbBr3 perovskite has attracted increasing attention due to its outstanding stability and excellent photoelectric characteristics compared with organic–inorganic counterparts. However, the electroluminescence (EL) efficiencies of inorganic CsPbBr3 perovskite light-emitting diodes (PeLEDs) are unsatisfactory because of high trap densities, which lead to non-radiative recombination loss. Herein, by introducing potassium bromide (KBr), we successfully prepare zero-dimensional/three-dimensional (0D/3D) Cs4−xKxPbBr6/CsPbBr3 heterostructure perovskite films with suppressed trap density and improved photoluminescence quantum yield (PLQY). The deep energy level of 0D Cs4−xKxPbBr6 phase is confirmed using DFT calculation. Moreover, the formation of the unique heterostructure inhibits the free charge diffusion at the grain boundary from suffering trapping and recombination, which facilitates efficient radiative recombination in the 3D CsPbBr3 phase. Therefore, the optimized green PeLEDs show a high external quantum efficiency (EQE) of 12.8%, which is a six-fold improvement over the pristine one (2.1%), and a maximum brightness of 39 400 cd m−2. Our work provides a rational charge carrier confinement strategy for developing high-performance PeLEDs and can be broadened to other potential perovskite materials, not restricted to the CsPbBr3-based perovskite films.

Here, a new strategy that combines accessible active sites and multiphase synergy in a simple process is developed for constructing bifunctional electrocatalysts toward overall water splitting. By using metal-organic framework nanosheets hydrothermally grown on the pre-oxidized nickel foam (denoted by Co2(OH)2(BDC)/NiO/NF) as a precursor, two novel heterogeneous nanosheet arrays including cobalt phosphide nanoparticles embedded carbon nanotubes nanosheet array supported by the phosphatized nickel foam (denoted by CoP-CNT/Ni2P/NF) and cobalt phosphide nanorods decorated carbon nanosheet array supported by the oxidized nickel foam (denoted by CoP-C/NiO/NF) are prepared. Both were confirmed to be high-efficient for hydrogen and oxygen evolution reactions. Especially, CoP-C/NiO/NF exhibits the higher catalytic activity toward hydrogen evolution reaction (η100 = -131 mV), promoted by the synergy of oxidized nickel foam. CoP-CNT/Ni2P/NF performs better in the oxygen evolution reaction (η50 = 301 mV), benefiting mainly from its improved electrochemically active surface area. The two catalysts match well in overall water splitting with satisfactory activity (η10 = 1.57 V ) and stability when directly applied in a two-electrode cell. This method will bring new inspiration to maximize the electrocatalytic efficiency of MOF-derived catalysts for energy conversion applications in the future.

Identification of the active species in electrocatalysts toward hydrogen evolution reaction (HER) is of great significance for the development of the catalytic industry; however, it is still the su...

GeTe is an important narrow bandgap semiconductor material and has found application in the fields of phase change storage as well as spintronics devices. However, it has not been studied for application in the field of infrared photovoltaic detectors working at room temperature. Herein, GeTe nanofilms were grown by magnetron sputtering technique and characterized to investigate its physical, electrical, and optical properties. A high-performance infrared photovoltaic detector based on GeTe/Si heterojunction with the detectivity of 8 × 1011 Jones at 850 nm light irradiation at room temperature was demonstrated.

Topological Dirac semimetals made of two-dimensional transition-metal dichalcogenides (TMDCs) have attracted enormous interest for use in electronic and optoelectronic devices because of their electron transport properties. As van der Waals materials with a strong interlayer interaction, these semimetals are expected to support layer-dependent plasmonic polaritons yet to be revealed experimentally. Here, we demonstrate the apparent retardation and attenuation of mid-infrared (MIR) plasmonic waves in type-II Dirac semimetal platinum tellurium (PtTe2) nanoribbons and nanoflakes by near-field nanoimaging. The attenuated dispersion relations for the plasmonic modes in the PtTe2 nanoribbons (15-25 nm thick) extracted from the near-field standing-wave patterns are applied for the fitting of PtTe2 permittivity in the MIR regime, indicating that both free carriers and Dirac fermions are involved in MIR light-matter interaction in PtTe2. The annihilation of plasmonic modes in the ultrathin (

Work function strongly impacts the surficial charge distribution, especially for metal-support electrocatalysts when a built-in electric field (BEF) is constructed. Therefore, studying the correlation between work function and BEF is crucial for understanding the intrinsic reaction mechanism. Herein, we present a Pt@CoOx electrocatalyst with a large work function difference (ΔΦ) and strong BEF, which shows outstanding hydrogen evolution activity in a neutral medium with a 4.5-fold mass activity higher than 20 % Pt/C. Both experimental and theoretical results confirm the interfacial charge redistribution induced by the strong BEF, thus subtly optimizing hydrogen and hydroxide adsorption energy. This work not only provides fresh insights into the neutral hydrogen evolution mechanism but also proposes new design principles toward efficient electrocatalysts for hydrogen production in a neutral medium. Agency for Science, Technology and Research (A*STAR) This work was financially supported by the Research Grants Council of Hong Kong (Poly U253009/18P) and the Hong Kong Polytechnic University (1-ZVGH). H.J.F. thanks the financial support from Agency for Science, Technology, and Research (A*STAR), Singapore by AME Individual Research Grants (A1983c0026).

Lieb lattice, a two-dimensional edge-centered square lattice, has attracted considerable interest due to its exotic electronic and topological properties. Although various optical and photonic Lieb lattices have been experimentally demonstrated, it remains challenging for an electronic Lieb lattice to be realized in real material systems. Here, based on first-principles calculations and tight-binding modeling, a silver sulfide (Ag

As a rising star in the family of two-dimensional (2D) materials, black phosphorus (BP) has recently attracted tremendous attention all over the world and demonstrated great potential in energy applications owing to its direct and narrow bandgap, high carrier mobility and theoretical capacity, as well as anisotropic structure. However, some critical issues remain to be studied before scalable production of BP for applications, such as preparation methods and performance. To fully explore its penitential applications, investigations based on BP are maximally covering from its intrinsic properties to energy conversion and storage. In this review, the significant advances recently made for the mechanism and application of BP in solar cells, Li /Ka-/Mg-/Na-ion and Li S batteries, supercapacitors, nanogenerators, solar water splitting and oxygen evolution reaction/hydrogen evolution reaction are summarized and discussed. Benefiting from the solid research in this field, the possible improvements and constructive suggestions regarding BP for enhancing its energy applications are provided.

Pseudocapacitance boosts the capacitance of supercapacitors by introducing additional redox sites with fast faradaic reactions. Here, we demonstrate the preparation of pseudocapacitive electrodes by inkjet printing bis-terpyridyl based molecular cobalt complexes as pseudocapacitive additives on laser induced graphene films. The substrate temperature during inkjet printing can effectively tune the morphology of the pseudocapacitive additives by overcoming the influence of coffee ring effect. Under optimum conditions, the capacitance of the pseudocapacitive electrodes was enhanced for 75 times over pristine graphene films. This approach can also be employed for the deposition of other functional materials via inkjet printing.

Developing efficient bifunctional electrocatalysts and gaining fundamental understanding of reaction mechanisms are crucial for practical water splitting. Herein, a bifunctional NiSe2 nanoparticles/carbon fiber paper (NSN/CFP) electrode is fabricated by the pyrolysis of Ni(NO3)2 on CFP, followed by a selenization step. The as-prepared electrocatalysts exhibit superior overall water splitting behavior in 1 M KOH with low overpotentials of 145 mV and 280 mV at current densities of 10 mA cm−2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) respectively, comparable to the performance of 20% Pt/C and RuO2. Detailed compositional and morphological studies reveal that the NiSe2 gradually transforms into an amorphous Ni(OH)2/NiOOH heterojunction during both HER and OER in alkaline medium. Based on these experimental results, an oxidation-induced self-reconstruction mechanism is proposed. Owing to the highly-oxidized Ni(OH)2/NiOOH active species, the self-reconstructed structure enhances the water splitting under fixed potentials for a prolonged time of 96 h with negligible current degradation. This work not only provides a facile route to fabricate efficient and stable electrocatalysts for large-scale water splitting but also reveals an underlying structural evolution mechanism, which guides the rational design of heterogeneous catalysts.

ZrTe2 is a candidate topological material from the layered two-dimensional transition-metal dichalcogenide family, and thus the material may show exotic electrical transport properties and may be p...

The newly developed van der Waals materials allow fabrication of multilayer heterostructures. Early efforts have mostly focused on heterostructures formed by similar materials. More recently, however, attempts have been made to expand the types of materials, such as topological insulators and organic semiconductors. Here we introduce an amorphous semiconductor to the material library for constructing van der Waals heterostructures. Samples composed of 2 nm amorphous black phosphorus synthesized by pulsed laser deposition and monolayer WS2 obtained by mechanical exfoliation were fabricated by dry transfer. Photoluminescence measurements revealed that photocarriers excited in WS2 of the heterostructure transfer to amorphous black phosphorus, in the form of either energy or charge transfer, on a time scale shorter than the exciton lifetime in WS2. Transient absorption measurements further indicate that holes can efficiently transfer from WS2 to amorphous black phosphorus. However, interlayer electron transfer in either direction was found to be absent. The lack of electron transfer from amorphous black phosphorus to WS2 is attributed to the localized electronic states in the amorphous semiconductor. Furthermore, we show that a hexagonal BN bilayer can effectively change the hole transfer process.

We report a simple and scalable synthesis of MnSe2 nanocubes as the Na-ion battery anode materials . The as-prepared MnSe 2 nanocubes electrode achieves a four-electron reaction with an enhanced reversible capacity 249 mAh g−1 at 0.1 A g−1 and a 90.8% capacity retention after 100 cycles, which could be attributed to the particle-size decreasing from micrometer to nanometer scale and the usage of diglyme-based electrolyte. This work envisions the great potential of nano-sized metal selenides toward Na+ ion storage.