Progress on Two-Dimensional Transitional Metal Dichalcogenides Alloy Materials: Growth, Characterisation, and Optoelectronic Applications.

Two-dimensional (2D) transitional metal dichalcogenides (TMDs) have garnered remarkable attention in electronics, optoelectronics, and hydrogen precipitation catalysis due to their exceptional physicochemical properties. Their utilisation in optoelectronic devices is especially notable for overcoming graphene's zero-band gap limitation. Moreover, TMDs offer advantages such as direct band gap transitions, high carrier mobility, and efficient switching ratios. Achieving precise adjustments to the electronic properties and band gap of 2D semiconductor materials is crucial for enhancing their capabilities. Researchers have explored the creation of 2D alloy phases through heteroatom doping, a strategy employed to fine-tune the band structure of these materials. Current research on 2D alloy materials encompasses diverse aspects like synthesis methods, catalytic reactions, energy band modulation, high-voltage phase transitions, and potential applications in electronics and optoelectronics. This paper comprehensively analyses 2D TMD alloy materials, covering their growth, preparation, optoelectronic properties, and various applications including hydrogen evolution reaction catalysis, field-effect transistors, lithium-sulphur battery catalysts, and lasers. The growth process and characterisation techniques are introduced, followed by a summary of the optoelectronic properties of these materials.

Applications and Advances in Machine Learning Force Fields.

Force fields (FFs) form the basis of molecular simulations and have significant implications in diverse fields such as materials science, chemistry, physics, and biology. A suitable FF is required to accurately describe system properties. However, an off-the-shelf FF may not be suitable for certain specialized systems, and researchers often need to tailor the FF that fits specific requirements. Before applying machine learning (ML) techniques to construct FFs, the mainstream FFs were primarily based on first-principles force fields (FPFF) and empirical FFs. However, the drawbacks of FPFF and empirical FFs are high cost and low accuracy, respectively, so there is a growing interest in using ML as an effective and precise tool for reconciling this trade-off in developing FFs. In this review, we introduce the fundamental principles of ML and FFs in the context of machine learning force fields (MLFF). We also discuss the advantages and applications of MLFF compared to traditional FFs, as well as the MLFF toolkits widely employed in numerous applications.

Realization of Oriented and Nanoporous Bismuth Chalcogenide Layers via Topochemical Heteroepitaxy for Flexible Gas Sensors.

Most van der Waals two-dimensional (2D) materials without surface dangling bonds show limited surface activities except for their edge sites. Ultrathin Bi2Se3, a topological insulator that behaves metal-like under ambient conditions, has been overlooked on its surface activities. Herein, through a topochemical conversion process, ultrathin nanoporous Bi2Se3 layers were epitaxially deposited on BiOCl nanosheets with strong electronic coupling, leading to hybrid electronic states with further bandgap narrowing. Such oriented nanoporous Bi2Se3 layers possessed largely exposed active edge sites, along with improved surface roughness and film forming ability even on inkjet-printed flexible electrodes. Superior room-temperature NO2 sensing performance was achieved compared to other 2D materials under bent conditions. Our work demonstrates that creating nanoscale features in 2D materials through topochemical heteroepitaxy is promising to achieve both favorable electronic properties and surface activity toward practical applications.

Room-temperature epitaxial welding of 3D and 2D perovskites.

Formation of epitaxial heterostructures via post-growth self-assembly is important in the design and preparation of functional hybrid systems combining unique properties of the constituents. This is particularly attractive for the construction of metal halide perovskite heterostructures, since their conventional solution synthesis usually leads to non-uniformity in composition, crystal phase and dimensionality. Herein, we demonstrate that a series of two-dimensional and three-dimensional perovskites of different composition and crystal phase can form epitaxial heterostructures through a ligand-assisted welding process at room temperature. Using the CsPbBr3/PEA2PbBr4 heterostructure as a demonstration, in addition to the effective charge and energy transfer across the epitaxial interface, localized lattice strain was observed at the interface, which was extended to the top layer of the two-dimensional perovskite, leading to multiple new sub-bandgap emissions at low temperature. Given the versatility of our strategy, unlimited hybrid systems are anticipated, yielding composition-, interface- and/or orientation-dependent properties.

Inhibition of O-glycosylation aggravates GalN/LPS-induced liver injury through activation of ER stress.

OBJECTIVE: O-glycosylation is the most common post-translational modification of proteins, which is involved in many pathophysiological processes including inflammation. Acute liver injury is characterized by an excessive, uncontrolled inflammatory response, but the effects of aberrant O-glycosylation on acute liver injury are yet to explore. Here we aimed to investigate the role of defective O-glycosylation in D-galactosamine (GalN)/lipopolysaccharide (LPS)-induced acute liver damage in mice. MATERIAL AND METHODS: Experimental mice were administrated with an O-glycosylation inhibitor (benzyl-a-GalNac, 5 mg/kg) at 24 h before administration of GalN/LPS. At 12 h after GalN/LPS administration, mice were sacrificed to collect blood and liver samples for further analysis. RESULTS: We found that benzyl-a-GalNac treatment-induced abundant expression of Tn antigen, which is an immature O-glycan representing abnormal O-glycosylation. Benzyl-a-GalNac pretreatment exacerbated considerably GalN/LPS-induced liver damage in mice, evidenced by significantly reduced survival rates, more severe histological alterations, and notable elevation of multiple inflammatory cytokines and chemokines. Mechanistically, benzyl-a-GalNac could trigger endoplasmic reticulum (ER) stress in the liver of mice, demonstrated by the elevated expression of glucose-regulated protein 78 (GRP78) and C/EBP-homologous protein (CHOP), both of which are hallmarks for ER stress. Inhibition of ER stress by 4-phenylbutyric acid (4-PBA) markedly abrogated benzyl-a-GalNac-mediated enhanced hepatotoxicity and systemic inflammation in GalN/LPS-treated mice. CONCLUSIONS: This study demonstrated that inhibition of O-glycosylation caused by benzyl-a-GalNac aggravated GalN/LPS-induced liver damage and systemic inflammation, which may be due to activation of ER stress.

Stacking-Engineered Heterostructures in Transition Metal Dichalcogenides.

The layer-by-layer assembly of 2D transition metal dichalcogenide monolayer blocks to form a 3D stack, with a precisely chosen sequence/angle, is the newest development for these materials. In this way, one can create "van der Waals heterostructures (HSs)," opening up a new realm of materials engineering and novel devices with designed functionalities. Herein, a detailed systematic review of transition metal dichalcogenide stacking-engineered heterostructures, from controllable fabrication to typical characterization, and stacking-correlated physical behaviors is presented. Furthermore, recent advances in stacking design, such as stacking sequence, twist angles, and moiré superlattice heterojunctions, are also comprehensively summarized. Finally, the remaining challenges and possible strategies for using stacking engineering to tune the properties of 2D materials are also outlined.

Perovskite Light-Emitting Diodes with Near Unit Internal Quantum Efficiency at Low Temperatures.

Room-temperature-high-efficiency light-emitting diodes based on metal halide perovskite FAPbI3 are shown to be able to work perfectly at low temperatures. A peak external quantum efficiency (EQE) of 32.8%, corresponding to an internal quantum efficiency of 100%, is achieved at 45 K. Importantly, the devices show almost no degradation after working at a constant current density of 200 mA m-2 for 330 h. The enhanced EQEs at low temperatures result from the increased photoluminescence quantum efficiencies of the perovskite, which is caused by the increased radiative recombination rate. Spectroscopic and calculation results suggest that the phase transitions of the FAPbI3 play an important role for the enhancement of exciton binding energy, which increases the recombination rate.

Recent advances of small molecule fluorescent probes for distinguishing monoamine oxidase-A and monoamine oxidase-B in vitro and in vivo.

Monoamine oxidases (MAO-A and MAO-B) are the two flavin adenine dinucleotide (FAD) enzymes that play an important role in neurotransmitter homeostasis and in protection against biogenic amines. The two MAO enzymes are related to various diseases such as neurological disorders, cancer or other systemic diseases. It is crucial to distinguish these two subtypes in order to explore the pathogenesis and pathophysiology of different diseases. In this review, the relationship between MAOs and related diseases is briefly introduced. Additionally, we summarize the recent advances in small molecule fluorescent probes for specific detection of MAO-A and MAO-B.

Enhanced Carrier-Exciton Interactions in Monolayer MoS2 under Applied Voltages.

Carrier-exciton interactions in two-dimensional transition metal dichalcogenides (TMDs) is one of the crucial elements for limiting the performance of their optoelectronic devices. Here, we have experimentally studied the carrier-exciton interactions in a monolayer MoS2-based two-terminal device. Such two-terminal device without a gate electrode is generally considered as invalid to modulate the carrier concentration in active materials, while the photoluminescence peak exhibits a red shift and decay with increasing applied voltages. Time-resolved photoluminescence spectroscopy and photoluminescence multipeak fittings verify that such changes of photoluminescence peaks result from enhanced carrier-exciton interactions with increasing electron concentration induce the charged exciton increasing. To characterize the level of the carrier-exciton interactions, a quantitative relationship between the Raman shift of out-of-plane mode and changes in electron concentration has been established using the mass action model. This work provides an appropriate supplement for understanding the carrier-exciton interactions in TMD-based two-terminal optoelectronic devices.

Stirring revealed new functions of ethylenediamine and hydrazine in the morphology control of copper nanowires.

Cu nanowires, as promising candidates in many fields because of their merits, are commonly prepared by the solution phase based synthesis which is a simple and scalable method. However, precise control of the morphology, particularly surface roughness, of Cu nanowires is still challenging; and moreover, detailed formation mechanisms of Cu nanowires, in solution phase based synthesis, are still unclear. We here show the morphology manipulation of Cu nanowires by adjusting the stirring rate and the amounts of ethylenediamine and hydrazine (N2H4), yielding Cu nanowires with either smooth or rough surface. Importantly, according to our experimental results and theoretical investigation, new functions of ethylenediamine and N2H4 are found, and a growth process of Cu nanowires is proposed accordingly. In addition to typically accepted roles of ethylenediamine and N2H4, we find that ethylenediamine can facilitate the growth of Cu nanowires by etching Cu oxides and even Cu on the surface of Cu nanowires. Meanwhile, N2H4 molecules can modulate the growth of Cu nanowires as a capping agent, which can be easily influenced by stirring. Additionally, the as-synthesized Cu nanowires with different morphologies exhibit different optical and catalytic properties. This study provides new fundamental insights into the growth mechanism of Cu nanowires, and thus can facilitate controlled synthesis of Cu nanowires for further applications, including electronics, catalysis, and sensing.

Nitrogen Boosts Defective Vanadium Oxide from Semiconducting to Metallic Merit.

2D metal oxide nanosheets have attracted substantial attention for various applications owing to their appealing advantages. Yet, the exploration of effective methodology for fabrication of metallic 2D metal oxides with a high concentration of N dopants in a scalable manner remains challenging. Herein, a topochemical strategy is demonstrated on vanadium oxide nanosheets by combining 2D nanostructuring, heteroatom-doping, and defect engineering for modulating their intrinsic electronic structure and greatly enhancing their electrochemical property. O vacancies and N dopants (VON and VN bonds) are in situ formed in vanadium oxide via nitridation and lead to semiconductive-to-metallic phase transformation evidenced by experimental results and theoretical calculation. Overall, the N-VO0.9 nanosheets exhibit a metallic electron transportation behavior and excellent electrochemical performance. These findings shed light on the rational design and electron structure tuning of 2D nanostructures for energy and electronics applications.

Pressure-Engineered Structural and Optical Properties of Two-Dimensional (C4H9NH3)2PbI4 Perovskite Exfoliated nm-Thin Flakes.

Resolving the structure-property relationships of two-dimensional (2D) organic-inorganic hybrid perovskites is essential for the development of photovoltaic and photoelectronic devices. Here, pressure (0-10 GPa) was applied to 2D hybrid perovskite flakes mechanically exfoliated from butylammonium lead halide single crystals, (C4H9NH3)2PbI4, from which we observed a series of changes of the strong excitonic emissions in the photoluminescence spectra. By correlating with in situ high-pressure X-ray diffraction results, we examine successfully the relationship between structural modifications in the inorganic PbI42- layer and their excitonic properties. During the transition between Pbca (1b) phase and Pbca (1a) phase at around 0.1 GPa, the decrease in ⟨Pb-I-Pb⟩ bond angle and increase in Pb-I bond length lead to an abrupt blue shift of the excitonic bandgap. The presence of the P21/a phase above 1.4 GPa increases the ⟨Pb-I-Pb⟩ bond angle and decreases the Pb-I bond length, leading to a deep red shift of the excitonic bandgap. The total band gap narrowing of ∼350 meV to 2.03 eV at 5.3 GPa before amorphization, facilitates (C4H9NH3)2PbI4 as a much better solar absorber. Moreover, phase transitions inevitably modify the carrier lifetime of (C4H9NH3)2PbI4, where an initial 150 ps at ambient phase is prolongated to 190 ps in the Pbca (1a) phase along with enhanced photoluminescence (PL), originating from pressure-induced strong radiative recombination of trapped excitons.The onset of P21/a phase shortens significantly the carrier lifetime to 53 ps along with a weak PL emission due to pressure-induced severe lattice distortion and amorphization. High-pressure study on (C4H9NH3)2PbI4 nm-thin flakes may provide insights into the mechanisms for synthetically designing novel 2D hybrid perovskite based photoelectronic devices and solar cells.

Realization of vertical metal semiconductor heterostructures via solution phase epitaxy.

The creation of crystal phase heterostructures of transition metal chalcogenides, e.g., the 1T/2H heterostructures, has led to the formation of metal/semiconductor junctions with low potential barriers. Very differently, post-transition metal chalcogenides are semiconductors regardless of their phases. Herein, we report, based on experimental and simulation results, that alloying between 1T-SnS2 and 1T-WS2 induces a charge redistribution in Sn and W to realize metallic Sn0.5W0.5S2 nanosheets. These nanosheets are epitaxially deposited on surfaces of semiconducting SnS2 nanoplates to form vertical heterostructures. The ohmic-like contact formed at the Sn0.5W0.5S2/SnS2 heterointerface affords rapid transport of charge carriers, and allows for the fabrication of fast photodetectors. Such facile charge transfer, combined with a high surface affinity for acetone molecules, further enables their use as highly selective 100 ppb level acetone sensors. Our work suggests that combining compositional and structural control in solution-phase epitaxy holds promises for solution-processible thin-film optoelectronics and sensors.

High-Pressure-Induced Comminution and Recrystallization of CH3 NH3 PbBr3 Nanocrystals as Large Thin Nanoplates.

High pressure (HP) can drive the direct sintering of nanoparticle assemblies for Ag/Au, CdSe/PbS nanocrystals (NCs). Instead of direct sintering for the conventional nanocrystals, this study experimentally observes for the first time high-pressure-induced comminution and recrystallization of organic-inorganic hybrid perovskite nanocrystals into highly luminescent nanoplates with a shorter carrier lifetime. Such novel pressure response is attributed to the unique structural nature of hybrid perovskites under high pressure: during the drastic cubic-orthorhombic structural transformation at ≈2 GPa, (301) the crystal plane fully occupied by organic molecules possesses a higher surface energy, triggering the comminution of nanocrystals into nanoslices along such crystal plane. Beyond bulk perovskites, in which pressure-induced modifications on crystal structures and functional properties will disappear after pressure release, the pressure-formed variants, i.e., large (≈100 nm) and thin (<10 nm) perovskite nanoplates, are retained and these exhibit simultaneous photoluminescence emission enhancing (a 15-fold enhancement in the photoluminescence) and carrier lifetime shortening (from ≈18.3 ± 0.8 to ≈7.6 ± 0.5 ns) after releasing of pressure from 11 GPa. This pressure-induced comminution of hybrid perovskite NCs and a subsequent amorphization-recrystallization treatment offer the possibilities of engineering the advanced hybrid perovskites with specific properties.

Pressure-Induced Phase Transition in Weyl Semimetallic WTe2.

Tungsten ditelluride (WTe2 ) is a semimetal with orthorhombic Td phase that possesses some unique properties such as Weyl semimetal states, pressure-induced superconductivity, and giant magnetoresistance. Here, the high-pressure properties of WTe2 single crystals are investigated by Raman microspectroscopy and ab initio calculations. WTe2 shows strong plane-parallel/plane-vertical vibrational anisotropy, stemming from its intrinsic Raman tensor. Under pressure, the Raman peaks at ≈120 cm-1 exhibit redshift, indicating structural instability of the orthorhombic Td phase. WTe2 undergoes a phase transition to a monoclinic T' phase at 8 GPa, where the Weyl states vanish in the new T' phase due to the presence of inversion symmetry. Such Td to T' phase transition provides a feasible method to achieve Weyl state switching in a single material without doping. The new T' phase also coincides with the appearance of superconductivity reported in the literature.

Phase evolution of lithium intercalation dynamics in 2H-MoS2.

Due to the easy intralayer gliding and weak interlayer van der Waals interaction in transition metal dichalcogenides (TMDs), ion (particularly Li+) intercalation has been used to modify and tune their atomic structures to obtain the desired optical, electronic and chemical properties for future optoelectronics and energy storage applications. A good understanding of the transformative structures during intercalation is critical. In this paper, we investigate the structural transformation dynamics of 2H-MoS2 using electrochemical Li+ intercalation for 2H-MoS2. The introduction of Li+ changes the local symmetry of the MoS2 in favor of the dT phase, clearly indicated by the appearance of Raman peaks of the dT phase. Further Li+ insertion causes the samples to become single-layer-like, characterized by the disappearance of the 32 cm-1 Raman peak. We also observe for the first time that the photoluminescence (PL) emission gradually redshifts with decreasing intensity, followed by eventual vanishing of the PL peak in the dT-MoS2 phase. By the nudged elastic band (NEB) calculations, we propose the 2H-1T-dT phase transition mechanism of MoS2 for Li+ intercalated samples. Our claims are supported by high resolution-transmission electron microscopy (HR-TEM). Our study deepens the understanding of the phase transition dynamics upon lithium intercalation, which is of great value to possible optoelectronic devices based on the phase engineering of TMDs. The new Li-stabilized dT-MoS2 phase does not possess inversion symmetry and may present a feasible way to achieve Weyl state tuning in a single material via phase engineering.

High Mobility 2D Palladium Diselenide Field-Effect Transistors with Tunable Ambipolar Characteristics.

Due to the intriguing optical and electronic properties, 2D materials have attracted a lot of interest for the electronic and optoelectronic applications. Identifying new promising 2D materials will be rewarding toward the development of next generation 2D electronics. Here, palladium diselenide (PdSe2 ), a noble-transition metal dichalcogenide (TMDC), is introduced as a promising high mobility 2D material into the fast growing 2D community. Field-effect transistors (FETs) based on ultrathin PdSe2 show intrinsic ambipolar characteristic. The polarity of the FET can be tuned. After vacuum annealing, the authors find PdSe2 to exhibit electron-dominated transport with high mobility (µe (max) = 216 cm2 V-1 s-1 ) and on/off ratio up to 103 . Hole-dominated-transport PdSe2 can be obtained by molecular doping using F4 -TCNQ. This pioneer work on PdSe2 will spark interests in the less explored regime of noble-TMDCs.

Graphene homojunction: closed-edge bilayer graphene by pseudospin interaction.

Depending on the sublattices they are propagated in, low-energy electrons or holes are labeled with pseudospin. By engineering pseudospin interactions, we propose that two critical features of a junction, i.e., band gap opening and spatial charge separation, can be realized in graphene layers with proper stacking. We also demonstrate theoretically that such a graphene diode may play a role in future pseudospin electronics such as for harvesting solar energy.

Stacking-Dependent Interlayer Coupling in Trilayer MoS2 with Broken Inversion Symmetry.

The stacking configuration in few-layer two-dimensional (2D) materials results in different structural symmetries and layer-to-layer interactions, and hence it provides a very useful parameter for tuning their electronic properties. For example, ABA-stacking trilayer graphene remains semimetallic similar to that of monolayer, while ABC-stacking is predicted to be a tunable band gap semiconductor under an external electric field. Such stacking dependence resulting from many-body interactions has recently been the focus of intense research activities. Here we demonstrate that few-layer MoS2 samples grown by chemical vapor deposition with different stacking configurations (AA, AB for bilayer; AAB, ABB, ABA, AAA for trilayer) exhibit distinct coupling phenomena in both photoluminescence and Raman spectra. By means of ultralow-frequency (ULF) Raman spectroscopy, we demonstrate that the evolution of interlayer interaction with various stacking configurations correlates strongly with layer-breathing mode (LBM) vibrations. Our ab initio calculations reveal that the layer-dependent properties arise from both the spin-orbit coupling (SOC) and interlayer coupling in different structural symmetries. Such detailed understanding provides useful guidance for future spintronics fabrication using various stacked few-layer MoS2 blocks.

A flexible alkaline rechargeable Ni/Fe battery based on graphene foam/carbon nanotubes hybrid film.

The development of portable and wearable electronics has promoted increasing demand for high-performance power sources with high energy/power density, low cost, lightweight, as well as ultrathin and flexible features. Here, a new type of flexible Ni/Fe cell is designed and fabricated by employing Ni(OH)2 nanosheets and porous Fe2O3 nanorods grown on lightweight graphene foam (GF)/carbon nanotubes (CNTs) hybrid films as electrodes. The assembled f-Ni/Fe cells are able to deliver high energy/power densities (100.7 Wh/kg at 287 W/kg and 70.9 Wh/kg at 1.4 kW/kg, based on the total mass of active materials) and outstanding cycling stabilities (retention 89.1% after 1000 charge/discharge cycles). Benefiting from the use of ultralight and thin GF/CNTs hybrid films as current collectors, our f-Ni/Fe cell can exhibit a volumetric energy density of 16.6 Wh/l (based on the total volume of full cell), which is comparable to that of thin film battery and better than that of typical commercial supercapacitors. Moreover, the f-Ni/Fe cells can retain the electrochemical performance with repeated bendings. These features endow our f-Ni/Fe cells a highly promising candidate for next generation flexible energy storage systems.