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Transition metal dichalcogenide (TMD) moiré superlattices have emerged as a significant area of study in condensed matter physics. Thanks to their superior optical properties, tunable electronic band structure, strong Coulomb interactions, and quenched electron kinetic energy, they offer exciting avenues to explore correlated quantum phenomena, topological properties, and light-matter interactions. In recent years, scanning tunneling microscopy (STM) has made significant impacts on the study of these fields by enabling intrinsic surface visualization and spectroscopic measurements with unprecedented atomic scale detail. Here, we spotlight the key findings and innovative developments in imaging and characterization of TMD heterostructures via STM, from its initial implementation on the in situ grown sample to the latest photocurrent tunneling microscopy. The evolution in sample design, progressing from a conductive to an insulating substrate, has not only expanded our control over TMD moiré superlattices but also promoted an understanding of their structures and strongly correlated properties, such as the structural reconstruction and formation of generalized two-dimensional Wigner crystal states. In addition to highlighting recent advancements, we outline upcoming challenges, suggest the direction of future research, and advocate for the versatile use of STM to further comprehend and manipulate the quantum dynamics in TMD moiré superlattices.

Robust electrochemical sustainability of tailored high‐performance nanocomposites is integral to advanced electrochemical energy conversion and storage (EECS) systems. Functions, such as nanoscale ionic‐diffusion distance, electrocatalytic reactions, electrical conductivity, and fluid distribution, of transition metal dichalcogenide (TMD)‐based nanostructures have been extensively designed and studied. However, challenges in materials selection, operational scalability, and design flexibility of TMD‐incorporated metal‐matrix composites (MMCs) consisting of non‐noble metallic nanostructures and their originating TMD materials have scarcely been studied. Highlighting the effectiveness of emerging additive manufacturing techniques in sustainable energy supply and storage, laser powder bed fusion (L‐PBF) can offer a directly added dual‐functionality to fabricated complex multimaterial and TMD‐incorporated MMC electrocatalytic electrodes. In this review, the characteristics of composite powder feedstock and optimizing process parameters are critically emphasized from another perspective to maintain a balance between mechanical robustness and enhanced electrochemical response. It is demonstrated how factors such as surface roughness, particle shape, and rheological characteristics of TMDs can influence the flowability of composite powder feedstock and the electrochemical performance of L‐PBF‐processed electrodes. The review further aims to contribute compiled information for use in the rapidly growing global market for advanced energy storage systems, underscoring the transformative potential of L‐PBF and TMD‐incorporated MMCs in modernizing the EECS components. [ABSTRACT FROM AUTHOR]

Metal sulfide-based composites have become increasingly common as materials used for electrodes in supercapacitors because of their excellent conductivity, electrochemical activity, and redox capacity. This study synthesized a composite of NiFeS@MoS2@rGO nanostructure using a simple hydrothermal approach. The synthesized nanocomposite consisted of the composite of nickel sulfide and iron sulfide doped with MoS2@rGO. A three-electrode cell is employed to investigate the electrochemical properties of the NiFeS@MoS2@rGO electrode. The results demonstrated an optimal specific capacitance of 3188 F/g at 1.4 A/g in a 1 M KOH electrolyte. Furthermore, a supercapattery is designed utilizing NiFeS@MoS2@rGO//AC as the positive electrode and activated carbon (AC) as the negative electrode materials. The resulting supercapattery is designed at a cell voltage of 1.6 V, achieving a specific capacity value of 189 C/g at 1.4 A/g. It also demonstrated an excellent energy density of 55 Wh/kg with an enhanced power density of 3800 W/kg. Furthermore, the hybrid device demonstrated remarkable stability with a cycling stability of 95% over 30,000 charge–discharge cycles at a current density of 1.4 A/g. The supercapattery, which has excellent energy storage capabilities, is used as a power source for operating different portable electronic devices. [ABSTRACT FROM AUTHOR]

Modulating the electronic structure of transition metal dichalcogenides (TMDs) via alloying is challenging despite the additional potential applications. In this study, a solvothermal reaction is used to synthesize composition‐tuned ReS2–VS2 (Re1‐xVxS2) alloy nanosheets featuring an expanded interlayer distance. Increasing x induces a phase transition from the semiconducting 1T″ phase ReS2 to the metallic 3R‐stacking 1T phase VS2. Alloying via homogeneous atomic mixing renders the nanosheets more metallic and with less oxidation than VS2. First‐principles calculations consistently predict the 1T″–1T phase transition of the atomically mixed alloy structures. The calculation also suggests that intercalation drives the 3R stacking of 1T phase VS2. The Re1‐xVxS2 nanosheets at x = 0.3–0.8 exhibit enhanced electrocatalytic activity toward water‐splitting hydrogen evolution reaction (HER) in an acid electrolyte. In situ X‐ray absorption fine structure measurements reveal that the metallicity of the alloys is fully retained during HER. The density of states and Gibbs free energy calculations show that alloying increases the metallicity and thus effectively activates the basal S atoms toward the HER, supporting the observed increased HER performance of the alloy nanosheets. [ABSTRACT FROM AUTHOR]

High‐performance 0D–2D hybrid photodetectors integrated with a crosslinker for direct pattering of quantum dots on the large‐scale synthesized MoS2 layer are reported. In the patterned hybrid structure, QD layers are patterned with a resolution of up to 2 µm, ensuring high precision. Enhanced charge transfer from QDs to 2D materials is confirmed using PL quenching, TR‐PL, and UPS analysis. As a result, the QD/2D hybrid photodetectors with crosslinker‐assisted direct patterning demonstrated a remarkable photoresponsivity of ≈105 A W−1 and a specific detectivity of over 1011 Jones, attributed to the difference in built‐in potential. The crosslinker patterning of QDs opens up potential applications for the photodetectors in highly integrated image sensors and can be further extended to high‐resolution display industries, eliminating unnecessary fabrication processes. [ABSTRACT FROM AUTHOR]

Doping semiconductors is crucial for controlling their carrier concentration and enabling their application in devices such as diodes and transistors. Furthermore, incorporating magnetic dopants can induce magnetic properties in semiconductors, paving the way for spintronic devices without an external magnetic field. This review highlights recent advances in growing doped, two-dimensional (2D) transition metal dichalcogenide (TMDC) semiconductors through various methods, like chemical vapor deposition, molecular beam epitaxy, chemical vapor transport, and flux methods. It also discusses approaches for achieving n- and p-type doping in 2D TMDC semiconductors. Notably, recent progress in doping 2D TMDC semiconductors to induce ferromagnetism and the development of quantum emitters is covered. Experimental techniques for achieving uniform doping in chemical vapor deposition and chemical vapor transport methods are discussed, along with the challenges, opportunities, and potential solutions for growing uniformly doped 2D TMDC semiconductors. [ABSTRACT FROM AUTHOR]

Materials exhibiting charge density waves are attracting increasing attention owing to their complex physics and potential for applications. In this paper, we present a computational, first principles-based study of the Janus monolayer of 1T-TaSSe transition metal dichalcogenide. We extensively compare the results with those obtained for parent compounds, TaS2 and TaSe2 monolayers, with confirmed presence of 13 × 13 charge density waves. The structural and electronic properties of the normal (undistorted) phase and distorted phase with 13 × 13 periodic lattice distortion are discussed. In particular, for a normal phase, the emergence of dipolar moment due to symmetry breaking is demonstrated, and its sensitivity to an external electric field perpendicular to the monolayer is investigated. Moreover, the appearance of imaginary energy phonon modes suggesting structural instability is shown. For the distorted phase, we predict the presence of a flat, weakly dispersive band related to the appearance of charge density waves, similar to the one observed in parent compounds. The results suggest a novel platform for studying charge density waves in two-dimensional transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

To facilitate water splitting using MoSe2 as a light absorber, we fabricated water‐dispersible MoSe2/C60‐dendron nanohybrids via physical modification of the basal plane of MoSe2. Upon photoirradiation, the mixed‐dimension MoSe2/C60 (2D/0D) heterojunction generates a charge‐separated state (MoSe2⋅+/C60⋅−) through electron extraction from the exciton in MoSe2 to C60. This process is followed by the hydrogen evolution reaction (HER) from water in the presence of a sacrificial donor (1‐benzyl‐1,4‐dihydronicotinamide) and co‐catalyst (Pt‐PVP). The apparent quantum yields of the HER were estimated to be 0.06 % and 0.27 % upon photoexcitation at the A‐ and B‐exciton absorption peaks (λmax=800 and 700 nm), respectively. [ABSTRACT FROM AUTHOR]

The demand for susceptible and selective hydrogen gas sensors is growing in fuel cells, chemical production, and automotive industries. Detecting H 2 gas at the ppm or ppb level is crucial due to its colourless, odourless, tasteless nature, as well as its flammability and explosiveness. Transition metal dichalcogenides (TMDs) and metal oxide (MO) semiconductors-based hybrid structures have garnered attention in recent years as promising candidates for gas sensing applications owing to their unique properties, including a high surface area, tunable bandgap, and strong gas adsorption. This paper aims to offer insights into the potential of TMD-MO hybrid structures as the next generation of hydrogen gas sensing platforms, contributing to developing highly sensitive and selective gas sensors for diverse industrial applications. TMD-MO hybrid structures are vital for detecting hydrogen gas with high sensitivity and selectivity, which are essential for safe and efficient hydrogen-based systems. Furthermore, these hybrid structures hold significant potential for further customization and enhancement to suit specific applications. Overall, TMD-MO hybrid structures offer a promising avenue for developing next-generation hydrogen gas sensors useable in various industrial applications and promoting a safe and sustainable hydrogen economy. [ABSTRACT FROM AUTHOR]

Layered two-dimensional materials are promising candidates for next-generation semiconductor platforms owing to their atomically thin bodies, and it is crucial to develop a method for their large-scale synthesis for integrating these materials into the fabrication process. Here, we report the synthesis of a centimeter-scale HfS2 ingot using the molten salt flux method (MSFM). The structure, crystallinity, and uniformity of the synthesized HfS2 sample were verified using X-ray diffraction and Raman spectroscopy. The chemical properties were investigated using X-ray photoelectron spectroscopy. A HfS2 synaptic field effect transistor (FET) was fabricated to confirm its electrical uniformity and semiconducting nature, with an average mobility of 10.6 cm2 V-1 s-1. The synaptic plasticity of the HfS2 synaptic FET was investigated by applying light pulses (405 nm) in different modulation configurations. Paired-pulse facilitation was achieved by applying a continuous light pulse with a negative gate bias voltage. The modulation of synaptic weight was demonstrated under different stimulation conditions, which emulates the human brain. Furthermore, the linearity of the HfS2 synaptic device was optimized based on the frequency of the pulses to enhance learning accuracy. The approach reported here encourages the large-scaled production of transition metal dichalcogenides (TMDs) for use in artificial synaptic transistors. [ABSTRACT FROM AUTHOR]

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The photoelectrocatalytic (PEC) hydrogen evolution reaction (HER) holds immense promise as a clean and sustainable method for hydrogen production. However, finding a suitable catalyst which is efficient, stable and scalable still remains an open challenge. BiOBr is a 2D layered material studied as photoelectrocatalyst because of its suitable band gap for light absorption and potential for up‐scalable production. However, its application in HER is not commonly reported, because of instability in a cathodic PEC environment, driven by a strong tendency to reduction to metallic bismuth. To solve this problem, 2D MoS2 is used to induce the formation of a van der Waals (vdW) layered heterojunction (HJ) to stabilize the lattice of BiOBr during HER. By performing PEC HER with the HJs containing different ratios of MoS2, it is found that the HJ with 1 % MoS2 can increase the stability of BiOBr, while the one with 50 % MoS2 can even accelerate the reduction of BiOBr to metallic bismuth. DFT calculations reveal that the interface between BiOBr and MoS2 in the HJ with 1 % MoS2 tends to push active electrons on the sulfur atoms, thus favoring HER. On the other hand, in the 50 % HJ, active electrons are prone to react with BiOBr to induce reduction. In situ wide‐angle X‐ray diffraction (WAXD) on the MoS2/BiOBr HJs with 1 % and 50 % of MoS2 allows to track the phase change and the phase transfer speed of BiOBr during PEC HER. Interestingly, when the HJ is illuminated with UV light, a lower amount of BiOBr is reduced to Bi under negative potential, due to the presence of photogenerated holes reacting with the extra electrons derived from the negative bias and preventing the BiOBr photon absorber to be further reduced. [ABSTRACT FROM AUTHOR]

High-dimensional entanglement of optical angular momentum has shown its enormous potential for increasing robustness and data capacity in quantum communication and information multiplexing, thus offering promising perspectives for quantum information science. To make better use of optical angular momentum entangled states, it is necessary to develop a reliable platform for measuring and analyzing them. Here, we propose a hybrid metadetector of monolayer transition metal dichalcogenide (TMD) integrated with spin Hall nanoantenna arrays for identifying Bell states of optical angular momentum. The corresponding states are converted into path-entangled states of propagative polaritonic modes for detection. Several Bell states in different forms are shown to be identified effectively. TMDs have emerged as an attractive platform for the next generation of on-chip optoelectronic devices. Our work may open up a new horizon for devising integrated quantum circuits based on these two-dimensional van der Waals materials. [ABSTRACT FROM AUTHOR]

The promise of two-dimensional (2D) rhenium diselenide (ReSe2) in electronics and optoelectronics has sparked considerable interest in this material. However, achieving the growth of high-quality ReSe2 thin films on a wafer scale remains a significant challenge. In this study, we adopted a two-step method to produce ReSe2 thin films by combining magnetron sputtering of Re and ReOx onto flat substrates with subsequent selenization via atmospheric pressure chemical vapor transport (CVT). After analyzing the produced films using X-ray diffraction to identify the crystalline phase in formed thin film and scanning electron microscopy (SEM) to examine surface morphology, it was determined that the suitable temperature range for the 15 min selenization process with CVT is 650 °C–750 °C. Further investigation of these optimally produced ReSe2 thin films included atomic force microscopy (AFM), X-ray photoelectron spectroscopy, and Raman spectroscopy. The bulk electrical analysis of these films and AFM and SEM surface morphology revealed a strong reliance on the type of precursor material used for their synthesis, whereas optical measurements indicated a potential for the films in non-linear optics applications, irrespective of the precursor or temperature used. This study not only provides a new pathway for the growth of ReSe2 films but also sheds light on the synthesis approaches of other 2D transition metal dichalcogenide materials. [ABSTRACT FROM AUTHOR]

The toxicity of 4-nitrophenol (4-NP) is one of the most common threats to the environment; therefore, developing a simple and sensitive analytical method to detect 4-NP is crucial. In this study, we prepared the Nd(OH)3/VSe2 nanocomposite using the simple hydrothermally assisted ultrasonication method and it was used to detect the 4-NP. Different characterization techniques were used to investigate the morphological and chemical compositions of Nd(OH)3/VSe2 nanocomposite. All of these investigations revealed that Nd(OH)3 nanoparticles were finely dispersed on the surface of the VSe2 nanosheet. The electrical conductivity of our prepared samples was evaluated by the electrochemical impedance spectroscopic technique. The CV and DPV methods were used to explore the electrochemical activity of 4-NP at the Nd(OH)3/VSe2/GCE sensor which exhibited a wide linear range (0.001 to 640 µM), low limit of detection (0.008 µM), and good sensitivity (0.41 µA µM−1 cm−2), respectively. Additionally, Nd(OH)3/VSe2/GCE sensor was tested in water samples for the detection of 4-NP, which exhibited good recovery results. The Nd(OH)3/VSe2 electrode material is a novel one for the electrochemical sensor field, and the obtained overall results also proved that our proposed material is an active material for sensor applications. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDC) are a family of atomic‐layer 2D materials (2dMs). Many researches have attempted to reinforce the unique properties by incorporating artificially designed nanostructures. Here, a highly photoluminescence (PL) enhancing platform is reported that is formed by combining high‐emittance plasmo–photonic metasurfaces with a large‐area 2dM, which is a continuous monolayer of TMDC of cm2 dimension. It is experimentally demonstrated that the 2dM‐PL intensity at room temperature is enhanced by more than 1030‐fold in comparison with that observed on the flat gold film regions. The enhancement is associated with spectral transformation indicating a resonant effect of the metasurfaces. It is moreover revealed that the confocal PL image originates from a coherent single‐mode emission that forms a photon number distribution obeying the Poisson probability distribution. Thus, the 2dM‐fused metasurfaces function as efficient coherent quantum light sources. PL decay‐time analysis also reveals the coexistence of two components in the enhanced PL. The fast component exhibits a lifetime of 18 ps whereas the slow component decays at 4.4 ns. Both components are most likely to undergo radiative processes, which indicates that metal‐induced PL quenching is suppressed on these 2dM‐fused metasurfaces. The long lifetime component is ascribed to an excitonic intervalley transition. [ABSTRACT FROM AUTHOR]

Hexagonal boron nitride (h‐BN) is a key ingredient for various 2D van der Waals heterostructure devices, but the exact role of h‐BN encapsulation in relation to the internal defects of 2D semiconductors remains unclear. Here, it is reported that h‐BN encapsulation greatly removes the defect‐related gap states by stabilizing the chemisorbed oxygen molecules onto the defects of monolayer WS2 crystals. Electron energy loss spectroscopy (EELS) combined with theoretical analysis clearly confirms that the oxygen molecules are chemisorbed onto the defects of WS2 crystals and are fixated by h‐BN encapsulation, with excluding a possibility of oxygen molecules trapped in bubbles or wrinkles formed at the interface between WS2 and h‐BN. Optical spectroscopic studies show that h‐BN encapsulation prevents the desorption of oxygen molecules over various excitation and ambient conditions, resulting in a greatly lowered and stabilized free electron density in monolayer WS2 crystals. This suppresses the exciton annihilation processes by two orders of magnitude compared to that of bare WS2. Furthermore, the valley polarization becomes robust against the various excitation and ambient conditions in the h‐BN encapsulated WS2 crystals. [ABSTRACT FROM AUTHOR]

Recently, a smart strategy for two-dimensional (2D) materials synthesis has emerged, namely space-confined chemical vapor deposition (CVD). Its extreme case is the microreactor method, in which the growth substrate is face-to-face stacked on the source substrate. In order to grow 2D transition metal dichalcogenides by this method, transition metal oxides, dispersed in very small amounts on the source substrate, are used as source materials in most of the published reports. In this paper, a colloidal dispersion of MoS2 in saline solution is used and MoS2 nanosheets with various shapes, sizes (between 5 and 60 μm) and thicknesses (2–4 layers) have been synthesized. Small MoS2 flakes (regular or defective) are present on the surface of the nanosheets. Catalytic sites, undercoordinated atoms located at the edges of MoS2 flakes and nanosheets, are produced in a high number by a layer-plus-island (Stranski–Krastanov) growth mechanism. Several double-resonance Raman bands (at 147, 177, 187, 225, 247, 375 cm−1) are assignable to single phonon processes in which the excited electron is elastically scattered on a defect. The narrow 247 cm−1 peak is identified as a topological defect-activated peak. These findings highlight the potential of defect engineering in material property optimization, particularly for solar water splitting applications. [ABSTRACT FROM AUTHOR]

2D metal compounds, such as transition metal dichalcogenides (TMDs), layered double hydroxides (LDHs), and MXenes, are emerging as important electrocatalyst materials in the transition to a sustainable energy future. Aided by their high surface area, electrical conductivity, and tunable electronic properties, these materials have provided a crucial research thrust in enhancing the efficiency of green hydrogen production, fuel cells, and carbon reduction processes. Most importantly, the synthesis of nanostructured 2D compounds, while challenging, is the key to optimizing their catalytic performance. Recent advancements in this field have highlighted the potential of 2D metal compounds in revolutionizing energy conversion technologies, which entails the discovery of new material compositions, the development of novel synthetic routes, and the integration of these materials into practical energy conversion systems. This review presents an overview of the distinctive characteristics of nanoscale‐confined 2D metal compounds, the challenges encountered in their synthesis, and electrochemical applications. [ABSTRACT FROM AUTHOR]

Interface-engineered 3D porous MoS 2 -ReS 2 in-plane heterojunction improved the hydrogen evolution reaction performance in seawater splitting. [Display omitted] Constructing in-plane heterojunctions with high interfacial density using two-dimensional materials represents a promising yet challenging avenue for enhancing the hydrogen evolution reaction (HER) in water electrolysis. In this work, we report that three-dimensional porous MoS 2 –ReS 2 in-plane heterojunctions, fabricated via chemical vapor deposition, exhibit robust electrocatalytic activity for the water splitting reaction. The optimized MoS 2 –ReS 2 in-plane heterojunction achieves superior HER performance across a wide pH range, requiring an overpotential of only 200 mV to reach a current density of 10 mA cm−2 in alkaline seawater. Thus, it outperforms standalone MoS 2 and ReS 2. Furthermore, the catalyst exhibits remarkable stability, enduring up to 200 h in alkaline seawater. Experimental results coupled with density functional theory calculations confirm that electron redistribution at the MoS 2 –ReS 2 heterointerface is likely driven by disparities in in-plane work functions between the two phases. This leads to charge accumulation at the interface, thereby enhancing the adsorptive activity of S atoms toward H* intermediates and facilitating the dissociation of water molecules at the interface. This discovery offers valuable insights into the electrocatalytic mechanisms at the interface and provides a roadmap for designing high-performance, earth-abundant HER electrocatalysts suitable for practical applications. [ABSTRACT FROM AUTHOR]

Monolayer transition metal dichalcogenides (1L‐TMDs) exhibits distinct light emissions in the visible range, making them suitable for 2D optoelectronic applications. Photoluminescence quantum yield (PLQY) is a key factor for practical applications of 1L‐TMDs. However, the methods for PLQY measurements of 1L‐TMDs suffer from limitations due to the small sample size and typically low PLQY, which require a complex measurement setup. In this study, machine learning (ML) models are developed to predict the PLQY of monolayer tungsten disulfide (1L‐WS2) using data extracted from 1208 PL spectra and corresponding measurement conditions as the ML training and testing data set. The ML model shows a high accuracy with R2 value of 0.744 and a mean absolute percentage error of 44% in the prediction of widely ranged PLQYs of 1L‐WS2 from 0.07% to 38%. This data‐driven prediction not only enables the convenient PLQY estimation of 1L‐TMDs, but also helps in identifying key parameters influencing PLQYs. [ABSTRACT FROM AUTHOR]

This theoretical study focuses on the performance of the surface plasmon resonance (SPR) sensor by strategically including various heterostructures in between the plasmonic metal and sensing medium. The heterostructure consists of a wurtzite nitride semiconductor and a two-dimensional (2D) material, specifically transition-metal dichalcogenides (TMDC). The angular interrogation approach is used to assess the sensor's efficacy which includes all commonly used critical parameters. The study also outlines the range of refractive indices (RI) in the sensing medium that elicit exceptional and notable responses from the proposed SPR structure. Based on the sensitivity, detection accuracy (DA), and figure of merit (FOM) values, it is determined that a TMDC material, specifically tungsten disulfide (WS2), combined with a wurtzite nitride semiconductor (such as gallium nitride, indium nitride, or aluminum nitride), offers the best performance. Among all heterostructures, GaN-WS2 exhibits the highest sensitivity. In contrast, AlN-WS2 exhibits remarkable performance in terms of DA, FOM, and the evanescent field intensity factor. Furthermore, the proposed SPR structure with InN-WS2 demonstrates maximum shifts in resonance angle, occurring within sensing RI range of 1.372 to 1.389. Similarly, AlN-WS2 exhibits the maximum shifts in resonance angle within the range from 1.387 to 1.4. GaN-WS2, however, shows the strongest response to resonance angle shifts within the range from 1.38 to 1.396. [ABSTRACT FROM AUTHOR]

Guided exciton–polariton modes naturally exist in bare transition metal dichalcogenide (TMDC) layers due to self-hybridization between excitons and photons. However, these guided polariton modes exhibit a limited propagation distance owing to the substantial exciton absorption within the material. Here, we investigated the impact of hexagonal boron nitride (hBN) layers on guided exciton–polariton modes in WS2 multilayers. By integrating hBN layers, we demonstrate a notable enhancement in the quality of guided exciton–polariton modes. The hBN layers can reduce substrate surface roughness and provide surface protection for the WS2 layer, mitigating inhomogeneous broadening of the exciton resonance. Consequently, we experimentally observed that the propagation distance of polariton modes substantially increased with hBN layers. Additionally, the polariton spectrum broadened due to efficient exciton relaxation to the polariton states at lower energies. Comparison with simulation data emphasizes that the observed improvements are primarily attributed to enhanced exciton quality. The promising outcomes with hBN encapsulation suggest its potential to overcome strong excitonic losses of the guided exciton polariton in implementing nanophotonic devices. Furthermore, this approach provides a new avenue for exploring the novel physics of guided exciton–polariton modes and their potential applications in polariton-based all-optical integrated circuits. [ABSTRACT FROM AUTHOR]

Abstract The ability to modulate optical and electrical properties of two-dimensional (2D) semiconductors has sparked considerable interest in transition metal dichalcogenides (TMDs). Herein, we introduce a facile strategy for modulating optoelectronic properties of monolayer MoSe2 with external light. Photochromic diarylethene (DAE) molecules formed a 2-nm-thick uniform layer on MoSe2, switching between its closed- and open-form isomers under UV and visible irradiation, respectively. We have discovered that the closed DAE conformation under UV has its lowest unoccupied molecular orbital energy level lower than the conduction band minimum of MoSe2, which facilitates photoinduced charge separation at the hybrid interface and quenches photoluminescence (PL) from monolayer flakes. In contrast, open isomers under visible light prevent photoexcited electron transfer from MoSe2 to DAE, thus retaining PL emission properties. Alternating UV and visible light repeatedly show a dynamic modulation of optoelectronic signatures of MoSe2. Conductive atomic force microscopy and Kelvin probe force microscopy also reveal an increase in conductivity and work function of MoSe2/DAE with photoswitched closed-form DAE. These results may open new opportunities for designing new phototransistors and other 2D optoelectronic devices.

Guided exciton–polariton modes naturally exist in bare transition metal dichalcogenide (TMDC) layers due to self-hybridization between excitons and photons. However, these guided polariton modes exhibit a limited propagation distance owing to the substantial exciton absorption within the material. Here, we investigated the impact of hexagonal boron nitride (hBN) layers on guided exciton–polariton modes in WS2 multilayers. By integrating hBN layers, we demonstrate a notable enhancement in the quality of guided exciton–polariton modes. The hBN layers can reduce substrate surface roughness and provide surface protection for the WS2 layer, mitigating inhomogeneous broadening of the exciton resonance. Consequently, we experimentally observed that the propagation distance of polariton modes substantially increased with hBN layers. Additionally, the polariton spectrum broadened due to efficient exciton relaxation to the polariton states at lower energies. Comparison with simulation data emphasizes that the observed improvements are primarily attributed to enhanced exciton quality. The promising outcomes with hBN encapsulation suggest its potential to overcome strong excitonic losses of the guided exciton polariton in implementing nanophotonic devices. Furthermore, this approach provides a new avenue for exploring the novel physics of guided exciton–polariton modes and their potential applications in polariton-based all-optical integrated circuits.

The acquisition of real-time temperature monitoring during photothermal therapy is significant to prevent unnecessary damage to healthy tissues. However, owing to complexity and diverse factors in microenvironment of cells, there still remain considerable challenges in achieving noninvasive temperature measurement and manipulation in therapeutic process. Herein, biocompatible Nd-doped MoSe2 nanosheets have been developed on the premise of excellent photothermal effect, which manifest desirable photoluminescence and distinct temperature self-monitored capability in near-infrared I and II bio-windows. Based on thermally coupled energy levels of Nd ions, the real-time monitoring on temperature changes in intracellular environment can be realized which provide instant temperature feedbacks to avoid side effects from hyperthermia. Exclusive of detrimental elements such as F and Pb, the objective nanosheets manifest satisfactory biosafety and can induce effective tumor ablation under near-infrared irradiation with photothermal conversion efficiency up to 40.8%, providing an innovative vision for developing more precisely and safely photothermal approaches.

Metal sulfide-based composites have become increasingly common as materials used for electrodes in supercapacitors because of their excellent conductivity, electrochemical activity, and redox capacity. This study synthesized a composite of NiFeS@MoS2@rGO nanostructure using a simple hydrothermal approach. The synthesized nanocomposite consisted of the composite of nickel sulfide and iron sulfide doped with MoS2@rGO. A three-electrode cell is employed to investigate the electrochemical properties of the NiFeS@MoS2@rGO electrode. The results demonstrated an optimal specific capacitance of 3188 F/g at 1.4 A/g in a 1 M KOH electrolyte. Furthermore, a supercapattery is designed utilizing NiFeS@MoS2@rGO//AC as the positive electrode and activated carbon (AC) as the negative electrode materials. The resulting supercapattery is designed at a cell voltage of 1.6 V, achieving a specific capacity value of 189 C/g at 1.4 A/g. It also demonstrated an excellent energy density of 55 Wh/kg with an enhanced power density of 3800 W/kg. Furthermore, the hybrid device demonstrated remarkable stability with a cycling stability of 95% over 30,000 charge–discharge cycles at a current density of 1.4 A/g. The supercapattery, which has excellent energy storage capabilities, is used as a power source for operating different portable electronic devices.

The ability to modulate optical and electrical properties of two-dimensional (2D) semiconductors has sparked considerable interest in transition metal dichalcogenides (TMDs). Herein, we introduce a facile strategy for modulating optoelectronic properties of monolayer MoSe2 with external light. Photochromic diarylethene (DAE) molecules formed a 2-nm-thick uniform layer on MoSe2, switching between its closed- and open-form isomers under UV and visible irradiation, respectively. We have discovered that the closed DAE conformation under UV has its lowest unoccupied molecular orbital energy level lower than the conduction band minimum of MoSe2, which facilitates photoinduced charge separation at the hybrid interface and quenches photoluminescence (PL) from monolayer flakes. In contrast, open isomers under visible light prevent photoexcited electron transfer from MoSe2 to DAE, thus retaining PL emission properties. Alternating UV and visible light repeatedly show a dynamic modulation of optoelectronic signatures of MoSe2. Conductive atomic force microscopy and Kelvin probe force microscopy also reveal an increase in conductivity and work function of MoSe2/DAE with photoswitched closed-form DAE. These results may open new opportunities for designing new phototransistors and other 2D optoelectronic devices. [ABSTRACT FROM AUTHOR]

This study investigates a successful fabrication of MoS2/Fe3O4/PANI composite by chemical co‐precipitation method. The facile hydrothermal approach was employed to synthesize a MoS2/Fe3O4 composite, followed by the utilization of a conventional chemical oxidation strategy to produce a PANI coating on the composite, thereby generating an active material for electrochemical reactions and a structure facilitating the transportation of ions via multiple pathways. The fabricated MoS2/Fe3O4/PANI composite was characterized by SEM, ICP, XRD, FT‐IR, and so on. In this study, we delved into the electrochemical charge storage feature of MoS2/Fe3O4/PANI. The electrochemical characteristics of the nanocomposite were assessed through the implementation of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry techniques in a 3 M KOH electrolytic solution, utilizing nickel foam as both a material support and current collector for two electrode configurations. The findings indicate that MoS2, as the support matrix, possesses notable attributes such as a substantial surface area, elevated electrical conductivity, and varied oxidation states. As a result, the electrical conductivity performance of the MoS2/Fe3O4/PANI composite, which includes well‐dispersed Fe3O4 nano‐cubes on the surfaces of MoS2, is significantly enhanced. In comparison to pure Fe3O4, the resultant composite revealed improved specific capacitances of 401 F/g at 1.25 A g−1, along with outstanding cyclic stability of 89.3 even after undergoing 5000 cycles. The superior electrochemical properties observed may be ascribed to both the proficient electrical conductivity of MoS2 and the incorporation of Fe3O4 particles, which are anchored onto the MoS2. The results prove that MoS2/Fe3O4/PANI hybrid composite holds as highly efficient electrode material for supercapacitor. [ABSTRACT FROM AUTHOR]

2D semiconducting transition metal dichalcogenides (TMDs) are emerging as promising candidates in the pursuit of advancing semiconductor technology. One major challenge for integrating 2D TMD materials into practical applications is developing an epitaxial technique with robust reproducibility for single‐oriented growth and thus single‐crystal growth. Here, the growth of single‐orientated MoS2 on c‐plane sapphire with atomically thin Fe2O3 decoration layers under various growth conditions is demonstrated. The statistical data highlight robust reproducibility, achieving a single orientation ratio of up to 99%. Density functional theory calculations suggest that MoS2 favors a 0° alignment ([112¯0]//[112¯0]$[ {11\bar{2}0} ]//\ [ {11\bar{2}0} ]$) on the Fe2O3 (0001) surface. This preference ensures single‐oriented growth, even on mirror‐reflected exposed surfaces which typically lead to antiparallel domains. Subsequent optical and electrical analyses confirm the uniformity and undoped nature of MoS2 on Fe2O3‐decorated sapphire, showing its quality is comparable to MoS2 grown on bared sapphires. The results underscore the potential of Fe2O3‐decorated sapphire as an effective substrate for the consistent and high‐quality epitaxial growth of 2D TMDs, illuminating the pathway to epitaxial control of 2D TMD orientation through strategic modulation of crystalline atomic surfaces. [ABSTRACT FROM AUTHOR]

Monolayer transition metal dichalcogenides are a class of atomically thin semiconductors that have a direct bandgap, making them promising candidates for optoelectronic and photonic devices. However, the low quantum yield at high charge injection levels significantly limits their applicability in optoelectronic devices that function under high current densities, such as light-emitting diodes and lasers. To address this issue, we demonstrate the use of hexagonal boron nitride encapsulation as a means of tuning the photoluminescence properties in monolayer transition metal dichalcogenides. Our results show a several-fold enhancement in the photoluminescence quantum yield at high exciton densities. This improvement is attributed to the suppressed exciton–exciton annihilation, which is supported by experimental time-resolved photoluminescence spectra and theoretical analysis. Our findings provide a simple and effective method for achieving highly efficient optoelectronic devices based on monolayer transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

Confronted with severe electromagnetic wave pollution, the development of high-performance electromagnetic wave shielding or absorbing materials is an effective way to deal with it. Notably, double transition metal alloys and transition metal dichalcogenides have attracted extensive attention in electromagnetic wave absorption, but few reports have studied the effects of these two materials on electromagnetic wave absorption at the same time. In this work, cobalt-based alloy with magnetic loss mechanism was selected for composition optimization. The ternary metal-organic framework was prepared by the one-step method, and then CoCu/C was prepared by high temperature annealing. Finally, in the hydrothermal process, ultra-thin tungsten selenide nanosheets were coated on the surface of magnetic component, and the final polyhedral WSe2/CoCu/C composites with multiple heterogeneous interfaces were obtained. The synergistic effect of dielectric and magnetic components optimizes impedance matching and allows more electromagnetic waves to enter the absorber. Subsequently, through the conduction loss of high conductivity graphitized carbon, interfacial polarization, and dipole polarization of heterogeneous interfaces between the components, the magnetic loss provided by CoCu alloy can work together to maximize the attenuation ability of electromagnetic waves. Exactly, the minimum reflection loss (RLmin) value of the composite reaches −53.43 dB when the matched thickness is 2.1 mm, while the maximum effective absorption bandwidth (EABmax) reaches 6.0 GHz at a thin thickness of 1.8 mm. This work provides some support and reference for the design of novel electromagnetic wave absorbing materials via the dielectric/magnetic loss synergistic mechanism. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) vertical van der Waals heterostructures (vdWHs) show great potential across various applications. However, synthesizing large-scale structures poses challenges owing to the intricate growth parameters, forming unexpected hybrid film structures. Thus, precision in synthesis and thorough structural analysis are essential aspects. In this study, we successfully synthesized large-scale structured 2D transition metal dichalcogenides (TMDs) via chemical vapor deposition using metal oxide (WO3 and MoO3) thin films and a diluted H2S precursor, individual MoS2, WS2 films and various MoS2/WS2 hybrid films (Type I: MoxW1−xS2 alloy; Type II: MoS2/WS2 vdWH; Type III: MoS2 dots/WS2). Structural analyses, including optical microscopy, Raman spectroscopy, transmission electron microscopy (TEM) with energy-dispersive X-ray spectroscopy, and cross-sectional imaging revealed that the A1g and E2g modes of WS2 and MoS2 were sensitive to structural variations, enabling hybrid structure differentiation. Type II showed minimal changes in the MoS2′s A1g mode, while Types I and III exhibited a ~2.8 cm−1 blue shift. Furthermore, the A1g mode of WS2 in Type I displayed a 1.4 cm−1 red shift. These variations agreed with the TEM-observed microstructural features, demonstrating strain effects on the MoS2–WS2 interfaces. Our study provides insights into the structural features of diverse hybrid TMD materials, facilitating their differentiation through Raman spectroscopy. [ABSTRACT FROM AUTHOR]

Manipulating the exciton dynamics in a heterobilayer (HB) composed of two transition metal dichalcogenides (TMDCs) is important in the development of photonic/plasmonic devices based on TMDC HBs. Here, the realization of such a manipulation in a MoS2/WS2 HB is reported by using a Si/Au hybrid nanocavity composed of a Si nanoparticle and an Au film, which is manifested in the modification in the photoluminescence (PL) of the embedded MoS2/WS2 HB. It is shown that a transition from PL quenching to PL enhancement can be achieved by adjusting the diameter of the Si nanoparticle, which modifies the plasmon resonance supported by the Si/Au nanocavity. More interestingly, it is demonstrated that the enhancement factor can be manipulated by shifting the exciton/trion resonance close to or far away from the plasmon resonance by simply increasing the laser power. It is revealed that the manipulation is realized by effectively controlling the strain and Purcell effects induced by the Si/Au nanocavity. A PL enhancement factor as large as ≈187 in the MoS2/WS2 HB at a high laser power is observed. The findings suggest the potential applications of dielectric‐metal hybrid nanocavities in the manipulation of the exciton dynamics in TMDC HBs and the development of novel plasmonic devices. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDs) are promising 2D materials which are attracting significant interest because of their distinctive physicochemical properties. The possibility of being exfoliated and dispersed in liquid solutions offers a viable pathway to scalable production. This personal account focuses on recent advancements in 2D TMD inks produced by liquid‐phase exfoliation (LPE) methods and intercalation‐based electrochemical exfoliation. In particular, different LPE production strategies, like ultrasonication LPE, high‐shear mixing exfoliation, and microfluidization, are introduced alongside a broad range of liquid media employed to provide functionalized TMD inks. The main advantage of TMD inks is its scalability, for practical applications in printed optoelectronics, energy storage, and conversion. Furthermore, the chemical functionalization of TMD inks can solve the poor electrical conductivity attributed to edge defects inherent in TMD inks. Finally, the ultimate orientations for future applications of chemically functionalized TMD devices are forecasted, with a specific focus on wearable and flexible printed electronics. [ABSTRACT FROM AUTHOR]

Extrusion-based additive manufacturing (EAM) provides design freedom and facilitates the production of complicated structures that are often challenging to produce using conventional processing methods. In this study, a TiO2 feedstock was developed by mixing TiO2 with a binder and optimized for extrusion. To maximize the reaction efficiency, three-dimensional (3D) structures were designed for the application of photocatalytic CO2 reduction. To further enhance the photocatalytic CO2 reduction efficiency of the structure, MoSe2, a transition metal dichalcogenide (TMD), was hydrothermally synthesized on the TiO2 surface to form a heterostructure. MoSe2, which is known for its affordability in fabrication heterostructures, high electrical conductivity, expanded light absorption range, and reduced bandgap, has the potential to enhance photocatalytic efficiency. The effectiveness of various TiO2–MoSe2 3D structural designs for CO2 reduction was evaluated. A custom-made stainless-steel reactor was used for CO2 reduction under UV-vis irradiation, followed by gas chromatography analysis of the produced gases. The optimized structure exhibited remarkable CO2 selectivity, reaching approximately 82%, demonstrating the feasibility of using EAM for fabricating 3D structures for photocatalytic CO2 reduction. [ABSTRACT FROM AUTHOR]

2D materials such as transition metal dichalcogenides (TMDCs) are a new class of atomic-layer materials possessing optical and electric properties that significantly depend on the number of layers. Electronic transitions can be manipulated in artificial resonant electromagnetic (EM) fields using metasurfaces and other designed nanostructures. Here, we demonstrate prominently resonant enhancement in the photoluminescence (PL) of atomic monolayer, WS2, doped with a small quantity of Mo. The excitonic PL showed a strong enhancement effect on a higher-order magnetic resonance of all-dielectric metasurfaces consisting of periodic arrays of Si nanopellets. The PL intensity witnessed a 300-fold enhancement compared to the reference PL intensity on a flat silicon dioxide (SiO2) layer, which suggests a drastic change in the dynamics of photoexcited states. Confocal PL microscopy and the analysis revealed that the single photons were coherently emitted from the TMDC monolayer on the metasurface. Furthermore, examining the PL lifetime in the ps and ns timescales clarified two exponential components at the prominent exciton PL: a short-time component decaying in 22 ps and a long-time component lasting over 10 ns. Therefore, we can infer that the radiative components were significantly activated in the TMDC monolayer on the metasurfaces in comparison to the reference monolayer on a flat SiO2 layer. [ABSTRACT FROM AUTHOR]

Two‐dimensional (2D) transition metal dichalcogenides (TMDs) have garnered significant attention in gas‐sensing applications due to their sensitive response to a wide range of gas molecules and their ability to operate at low temperatures, resulting in low‐power consumption. However, there are several areas that require improvement, including insufficient sensitivity at low detection limits, limited gas selectivity, low reliability, and poor recovery. To address these issues and enhance the performance of gas sensors, researchers have proposed the functionalization and hybridization of 2D TMDs. This review paper focuses on elucidating the synergistic effects of functionalization and hybridization of 2D TMDs with carbon‐related materials, metals, MOs, and metal chalcogenides. The paper presents an in‐depth analysis of the mechanisms involved in enhancing the performance of 2D TMD gas sensors and explores various synthesis methods for achieving functionalization and hybridization. Furthermore, the challenges currently faced in the field are discussed and offer insights into the future prospects of TMD nanocomposite‐based gas sensors. By comprehensively addressing these aspects, this research aims to contribute to the advancement of gas‐sensing technology using TMD nanocomposites. [ABSTRACT FROM AUTHOR]

Abstract Hexagonal boron nitride (h‐BN) is a key ingredient for various 2D van der Waals heterostructure devices, but the exact role of h‐BN encapsulation in relation to the internal defects of 2D semiconductors remains unclear. Here, it is reported that h‐BN encapsulation greatly removes the defect‐related gap states by stabilizing the chemisorbed oxygen molecules onto the defects of monolayer WS2 crystals. Electron energy loss spectroscopy (EELS) combined with theoretical analysis clearly confirms that the oxygen molecules are chemisorbed onto the defects of WS2 crystals and are fixated by h‐BN encapsulation, with excluding a possibility of oxygen molecules trapped in bubbles or wrinkles formed at the interface between WS2 and h‐BN. Optical spectroscopic studies show that h‐BN encapsulation prevents the desorption of oxygen molecules over various excitation and ambient conditions, resulting in a greatly lowered and stabilized free electron density in monolayer WS2 crystals. This suppresses the exciton annihilation processes by two orders of magnitude compared to that of bare WS2. Furthermore, the valley polarization becomes robust against the various excitation and ambient conditions in the h‐BN encapsulated WS2 crystals.

2D materials such as transition metal dichalcogenides (TMDCs) are a new class of atomic-layer materials possessing optical and electric properties that significantly depend on the number of layers. Electronic transitions can be manipulated in artificial resonant electromagnetic (EM) fields using metasurfaces and other designed nanostructures. Here, we demonstrate prominently resonant enhancement in the photoluminescence (PL) of atomic monolayer, WS2, doped with a small quantity of Mo. The excitonic PL showed a strong enhancement effect on a higher-order magnetic resonance of all-dielectric metasurfaces consisting of periodic arrays of Si nanopellets. The PL intensity witnessed a 300-fold enhancement compared to the reference PL intensity on a flat silicon dioxide (SiO2) layer, which suggests a drastic change in the dynamics of photoexcited states. Confocal PL microscopy and the analysis revealed that the single photons were coherently emitted from the TMDC monolayer on the metasurface. Furthermore, examining the PL lifetime in the ps and ns timescales clarified two exponential components at the prominent exciton PL: a short-time component decaying in 22 ps and a long-time component lasting over 10 ns. Therefore, we can infer that the radiative components were significantly activated in the TMDC monolayer on the metasurfaces in comparison to the reference monolayer on a flat SiO2 layer.

Doping semiconductors is crucial for controlling their carrier concentration and enabling their application in devices such as diodes and transistors. Furthermore, incorporating magnetic dopants can induce magnetic properties in semiconductors, paving the way for spintronic devices without an external magnetic field. This review highlights recent advances in growing doped, two-dimensional (2D) transition metal dichalcogenide (TMDC) semiconductors through various methods, like chemical vapor deposition, molecular beam epitaxy, chemical vapor transport, and flux methods. It also discusses approaches for achieving n- and p-type doping in 2D TMDC semiconductors. Notably, recent progress in doping 2D TMDC semiconductors to induce ferromagnetism and the development of quantum emitters is covered. Experimental techniques for achieving uniform doping in chemical vapor deposition and chemical vapor transport methods are discussed, along with the challenges, opportunities, and potential solutions for growing uniformly doped 2D TMDC semiconductors.

The promise of two-dimensional (2D) rhenium diselenide (ReSe2) in electronics and optoelectronics has sparked considerable interest in this material. However, achieving the growth of high-quality ReSe2 thin films on a wafer scale remains a significant challenge. In this study, we adopted a two-step method to produce ReSe2 thin films by combining magnetron sputtering of Re and ReOx onto flat substrates with subsequent selenization via atmospheric pressure chemical vapor transport (CVT). After analyzing the produced films using X-ray diffraction to identify the crystalline phase in formed thin film and scanning electron microscopy (SEM) to examine surface morphology, it was determined that the suitable temperature range for the 15 min selenization process with CVT is 650 °C–750 °C. Further investigation of these optimally produced ReSe2 thin films included atomic force microscopy (AFM), X-ray photoelectron spectroscopy, and Raman spectroscopy. The bulk electrical analysis of these films and AFM and SEM surface morphology revealed a strong reliance on the type of precursor material used for their synthesis, whereas optical measurements indicated a potential for the films in non-linear optics applications, irrespective of the precursor or temperature used. This study not only provides a new pathway for the growth of ReSe2 films but also sheds light on the synthesis approaches of other 2D transition metal dichalcogenide materials.

High-dimensional entanglement of optical angular momentum has shown its enormous potential for increasing robustness and data capacity in quantum communication and information multiplexing, thus offering promising perspectives for quantum information science. To make better use of optical angular momentum entangled states, it is necessary to develop a reliable platform for measuring and analyzing them. Here, we propose a hybrid metadetector of monolayer transition metal dichalcogenide (TMD) integrated with spin Hall nanoantenna arrays for identifying Bell states of optical angular momentum. The corresponding states are converted into path-entangled states of propagative polaritonic modes for detection. Several Bell states in different forms are shown to be identified effectively. TMDs have emerged as an attractive platform for the next generation of on-chip optoelectronic devices. Our work may open up a new horizon for devising integrated quantum circuits based on these two-dimensional van der Waals materials.

We unveil a highly efficient circular polarizer based on twisted double Td − WTe2 thin film in the transmissive and reflective modes. This polarizer can transform a linearly polarized incident wave into a circularly polarized one with extremely high extinction ratios by simply adjusting the orientation of the incident polarization plane. The proposed structure provides switching between the right-handed and left-handed circular polarizations (RCP and LCP) in the output wave by tuning the frequency and, in particular, the polarization direction of the incident wave. Furthermore, the twist angle of the thin films can control the handedness of the converted wave to be either LCP or RCP. Owing to the high efficiency of the polarization conversion and accessibility of the realization of the proposed structure, it may have potential applications as a polarization manipulator in the optical sensing, communication, and defense industry.