2D Transition Metal Dichalcogenides Materials Research Articles

MoSe2 nanosheets-based sensor for electrochemical detection of dopamine, ascorbic acid, and uric acid

There has been a growing interest in the field of transition metal dichalcogenide (TMD) materials and their potential applications in the field of electrochemical sensors. In the present work, molybdenum diselenide (MoSe2), as a typical representative of TMD, was prepared using a facile hydrothermal method and characterized in terms of its morphological and structural properties. Then, the obtained MoSe2 was dispersed in various solvents to investigate its electrocatalytic properties towards dopamine (DA), ascorbic acid (AA), and uric acid (UA). The electrochemical measurements revealed that deionized water is an effective solvent to disperse the MoSe2 and modify electrodes with the MoSe2 for electrochemical applications. Furthermore, the glassy carbon electrode (GCE) modified with the MoSe2, referred as GCE-MoSe2, was used as an electrochemical sensor to simultaneously detect the DA, AA, and UA. The GCE-MoSe2 exhibited wide linear detection with concentration ranges of 1–333 µM for DA, 50–3440 µM for AA, and 5–1146 µM for UA in phosphate buffer solution and low detection limits (LODs) of 0.57 µM, 13.7 µM, and 1.75 µM, respectively. The electrode further displayed good selectivity, reproducibility, and stability. This work provides valuable insights on constructing electrochemical sensing devices with high analytical performance using the important two-dimensional (2D) TMD materials.

Synthesis and Investigation of ReSe2 Thin Films Obtained from Magnetron Sputtered Re and ReOx

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.

Phase Transformation on Multilayer 2M-WS2 for Improved Surface-enhanced Raman Scattering.

In recent years, two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been widely recognized as an ideal platform for surface-enhanced Raman scattering (SERS). Given their rich structural phases, phase transformation in 2D TMDCs is an efficient strategy to tailor their SERS performance. In this paper, we present the great SERS performance of multilayer 2M-WS2 and then investigate the effect of its phase transformation on SERS performance. It is observed that multilayer 2M-WS2 nanosheets undergo a thermally induced single-crystal phase transition from 2M-WS2 to 2H-WS2 upon thermal annealing or laser treatment. Distinguishing from the commercially available pure 2H-WS2 (P-2H-WS2), 2H-WS2 obtained by annealing and laser treatment still retain SERS properties comparable to those of 2M-WS2, among which the detection limits for CV molecules (10-8 M) are 3 orders of magnitude lower than that of P-2H-WS2 and the Raman intensity enhancements are ∼10-37 times higher. In contrast to the charge transfer (CT) mechanism governed by the Fermi level in metallic-phase 2M-WS2, 2H-WS2 obtained by phase transition exhibits accelerated CT facilitated by the bandgap reduction and reorganization resulting from the abundance of vacancies. This study introduces an interesting perspective and potential avenue for enhancing SERS through metal-to-semiconductor phase transitions in 2D TMDCs materials.

Machine-learning-empowered identification of initial growth modes for 2D transition metal dichalcogenide thin films

In situ reflection high-energy electron diffraction (RHEED) is a powerful technique for monitoring surface states and offers invaluable insights into thin film growth. However, extracting hidden features and subtle changes from its vast data remains as a challenge. This work bridges the gap by employing machine learning (ML)-empowered RHEED analysis to elucidate the growth dynamics of two-dimensional (2D) transition metal dichalcogenide (TMDC) thin films grown under two distinct growth modes. Principal component analysis (PCA) and its modified processes were used to separate contributions of the graphene substrate and the MoSe2 film in the RHEED video. The ML-empowered RHEED analysis allowed us to effectively filter out the strong substrate signal and reconstructing RHEED videos solely for the MoSe2 films. This approach enabled detailed monitoring of film growth with unique features, and clearly distinguishing between the layer-by-layer growth mode and the island one. This work demonstrates the potentials of ML-empowered RHEED analysis for revealing complex growth dynamics of 2D TMDC materials, paving the way for advanced thin film monitoring and autonomous control in wider scope of thin film technologies.

Broadband tunable resonance modes from multi-composition monolayer MoS2(1−x)Se2x with SiO2 microsphere cavity

Two-dimensional (2D) monolayer transition metal dichalcogenides (TMDCs) that are compatible with Si-based substrates have already exhibited huge application potential in optoelectronics and photonics. The MoS2(1−x)Se2x ternary alloy consisting of two different chalcogens, as a class of lasing gain medium, enriches the family of 2D TMDC materials. Here, monolayer MoS2(1−x)Se2x ternary alloys with tunable composition have been synthesized via single-step chemical vapor deposition method. Raman and photoluminescence studies demonstrate that the bandgap of grown monolayer MoS2(1−x)Se2x alloys can be gradually tuned from 1.59 to 1.82 eV, indicating the continuous changes of the chemical composition x from 0.82 to 0. The oscillation characteristic is further investigated, where the MoS2(1−x)Se2x alloy provides optical gain for the SiO2 microsphere resonant cavity. The achieved resonance modes in a broadband range from 610 to 810 nm not only extend the range of potential TMDC-based lasers, but also drive the applications of alloy materials in various optoelectronics devices.

Defects and Defect Engineering of Two-Dimensional Transition Metal Dichalcogenide (2D TMDC) Materials.

As layered materials, transition metal dichalcogenides (TMDCs) are promising two-dimensional (2D) materials. Interestingly, the characteristics of these materials are transformed from bulk to monolayer. The atomically thin TMDC materials can be a good alternative to group III-V and graphene because of their emerging tunable electrical, optical, and magnetic properties. Although 2D monolayers from natural TMDC materials exhibit the purest form, they have intrinsic defects that limit their application. However, the synthesis of TMDC materials using the existing fabrication tools and techniques is also not immune to defects. Additionally, it is difficult to synthesize wafer-scale TMDC materials for a multitude of factors influencing grain growth mechanisms. While defect engineering techniques may reduce the percentage of defects, the available methods have constraints for healing defects at the desired level. Thus, this holistic review of 2D TMDC materials encapsulates the fundamental structure of TMDC materials, including different types of defects, named zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D). Moreover, the existing defect engineering methods that relate to both formation of and reduction in defects have been discussed. Finally, an attempt has been made to correlate the impact of defects and the properties of these TMDC materials.

Metatungstate Chemical Vapor Deposition of WSe2: Substrate Effects, Shapes, and Morphologies

Owing to their exceptional properties, which are usually determined by the growth conditions, 2D transition metal dichalcogenides (TMDCs) offer numerous research directions for applications in the fields of spintronics, valleytronics, and optoelectronics. Here, we focus on the chemical vapor deposition (CVD) synthesis of WSe2 (tungsten diselenide) nanoclusters/nanoflakes by using a liquid precursor for tungsten (ammonium metatungstate) on Si/SiO2, fused silica, and sapphire substrates. Various WSe2 clusters with different sizes, thicknesses, and geometries were analyzed by means of optical and atomic force microscopy (AFM) and Raman spectroscopy. The observed structures were mostly WSe2 multilayers; however, monolayer formations were also found. They showed significant morphological differences, as well as wide nucleation density and size variations, possibly related to precursor/substrate surface interactions under the same CVD synthesis conditions. The largest WSe2 domains with a lateral size of up to hundreds of micrometers were observed on sapphire, probably caused by a higher growth rate of singular nucleation sites. WSe2 domains with irregular and triangular shapes were simultaneously identified on fused silica, whereas multilayered pyramidal WSe2 structures dominated in the case of Si/SiO2 substrates. The application of polarized Raman spectroscopy to precisely determine and differentiate the characteristic vibrational modes (A1g, E2g, and 2LA(M)) enabled the unambiguous identification of 2D and/or multilayered WSe2 formations with a high crystallinity level. The presented comparative analysis of samples prepared in relatively simple synthesis conditions (moderate working temperatures and ambient pressure) provides a base for further progress of the facile metatungstate CVD method and relevant opportunities for the exploration of 2D TMDC materials.

Probing Polymorphic Stacking Domains in Mechanically Exfoliated Two-Dimensional Nanosheets Using Atomic Force Microscopy and Ultralow-Frequency Raman Spectroscopy.

As one of the key features of two-dimensional (2D) layered materials, stacking order has been found to play an important role in modulating the interlayer interactions of 2D materials, potentially affecting their electronic and other properties as a consequence. In this work, ultralow-frequency (ULF) Raman spectroscopy, electrostatic force microscopy (EFM), and high-resolution atomic force microscopy (HR-AFM) were used to systematically study the effect of stacking order on the interlayer interactions as well as electrostatic screening of few-layer polymorphic molybdenum disulfide (MoS2) and molybdenum diselenide (MoSe2) nanosheets. The stacking order difference was first confirmed by measuring the ULF Raman spectrum of the nanosheets with polymorphic stacking domains. The atomic lattice arrangement revealed using HR-AFM also clearly showed a stacking order difference. In addition, EFM phase imaging clearly presented the distribution of the stacking domains in the mechanically exfoliated nanosheets, which could have arisen from electrostatic screening. The results indicate that EFM in combination with ULF Raman spectroscopy could be a simple, fast, and high-resolution method for probing the distribution of polymorphic stacking domains in 2D transition metal dichalcogenide materials. Our work might be promising for correlating the interlayer interactions of TMDC nanosheets with stacking order, a topic of great interest with regard to modulating their optoelectronic properties.

Growth of Wafer-Scale Single-Crystal 2D Semiconducting Transition Metal Dichalcogenide Monolayers.

Due to extraordinary electronic and optoelectronic properties, large-scale single-crystal two-dimensional (2D) semiconducting transition metal dichalcogenide (TMD) monolayers have gained significant interest in the development of profit-making cutting-edge nano and atomic-scale devices. To explore the remarkable properties of single-crystal 2D monolayers, many strategies are proposed to achieve ultra-thin functional devices. Despite substantial attempts, the controllable growth of high-quality single-crystal 2D monolayer still needs to be improved. The quality of the 2D monolayer strongly depends on the underlying substrates primarily responsible for the formation of grain boundaries during the growth process. To restrain the grain boundaries, the epitaxial growth process plays a crucial role and becomes ideal if an appropriate single crystal substrate is selected. Therefore, this perspective focuses on the latest advances in the growth of large-scale single-crystal 2D TMD monolayers in the light of enhancing their industrial applicability. In the end, recent progress and challenges of 2D TMD materials for various potential applications are highlighted.

Atomically Thin Decoration Layers for Robust Orientation Control of 2D Transition Metal Dichalcogenides

Abstract2D 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 () 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.

The Role of Vacancy Dynamics in Two‐Dimensional Memristive Devices

AbstractTwo‐dimensional layered transition metal dichalcogenides (TMDCs) are promising memristive materials for neuromorphic computing systems. Despite extensive experimental work, the underlying switching mechanisms are still not understood, impeding progress in material and device functionality. This study reveals the dominant role of defect dynamics in the switching process of 2D TMDC materials. The switching process is governed by the formation and annihilation dynamics of a local vacancy depletion zone. It explains the distinct features of the device characteristics observed experimentally, including fundamentally different device behavior previously thought to originate from multiple mechanisms. Key influence factors are identified and discussed with a fully coupled and dynamic charge transport model for electrons, holes, and ionic point defects, including image‐charge‐induced Schottky barrier lowering (SBL). Thermal effects and local Joule heating are considered by coupling the transient heat transfer equation to the electronic properties. The model is validated with hysteresis and pulse measurements for various lateral 2D MoS2‐based devices, strongly corroborating the relevance of vacancy dynamics in TMDC devices and offering a new perspective on the switching mechanisms. The insights gained from this study can be used to extend the functional behavior of 2D TMDC memristive devices in future neuromorphic computing applications.

Controllable growth of wafer-scale two-dimensional WS2 with outstanding optoelectronic properties

As one of two-dimensional (2D) semiconductor materials, transition metal dichalcogenides (TMDs) have sparked enormous potential in next-generation electronics due to their unique and excellent physical, electronic and optical properties. Controllable growth of wafer-scale 2D TMDs is essential to realize the various high-end applications of TMDs, while it remains challenging. Herein, 2 inch 2D WS2 films were successfully synthesized by ambient pressure chemical vapor deposition based on substrate engineering and space-confined strategies. WS2 nucleation density can be effectively modulated depending on the annealing conditions of sapphire substrate. The thickness of WS2 films can be controllably fabricated by adjusting the space-confined height. Moreover, our strategies are demonstrated to be universal for the growth of other 2D TMD semiconductors. WS2-based photodetectors with different thicknesses were systematically investigated. Monolayer WS2 photodetector displays large responsivity of 0.355 A W−1 and high specific detectivity of 1.48 × 1011 Jones. Multilayer WS2 device exhibits negative self-powered photoresponse. Our work provides a new route for the synthesis of wafer-scale 2D TMD materials, paving the way for high performance integrated optoelectronic devices.

In-situ fabrication of vertical heterogeneous nickel diselenide-molybdenum diselenide architectures as bifunctional overall water-splitting electrocatalyst

Despite the rapid advances in electrocatalysts based on two-dimensional (2D) transition metal dichalcogenides (TMDs) materials, they are subject to serious aggregation, poor conductivity and the presence of inactive basal planes. Herein, we have successfully demonstrated the in-situ construction of NiSe2–MoSe2 heterostructure arrays on carbon cloth (NiSe2–MoSe2/CC) by a facile two-step hydrothermal process. The presence of the synergistic effect in the heterostructures effectively optimizes the poor conductivity and hydrophilicity, and thus enables fast electron transfer, leading to enhanced electrochemical reaction. Furthermore, density functional theory calculations reveal that the electrons redistribution at the heterojunction interface and the reduced Gibbs free energy of hydrogen adsorption for hydrogen evolution reaction (HER)/the Gibbs free energy change value of rate-determining step for oxygen evolution reaction (OER), thus enhancing the HER/OER catalytic activity. Importantly, the device displays a good performance with a low overpotential of 98 and 310 mV for HER and OER, respectively, and a low cell voltage of 1.59 V for its corresponding electrolyzer (10 mA cm−2). This work presents the high-performance water splitting of bifunctional electrocatalysts based on 2D TMDs materials and offers a novel design concept of interface engineering.

Effect of p-MoOx interfacial layer on the photovoltaic performances of p-MoS2/n-Si heterojunction solar cells by theoretical simulation

As one of particular 2D transition metal dichalcogenide materials, the outstanding properties of MoS2 enable the promising formation of superior homo or heterojunction solar cells. However, in the process of introducing oxygen treatment to modify the interface defects of MoS2/Si solar cells, or modulate the Fermi level of MoS2 films, a thin layer of p-MoOx capping layer is generally produced next to MoS2. In order to essentially clarify the functional mechanism of MoOx layer, p-MoS2/n-Si heterojunction solar cells with or without MoOx interfacial layer are simulated using SCAPS software. The influences of band gap, electron affinity, thickness of MoS2 and front contact barrier height on the performances of p-MoS2/n-Si solar cells are theoretically studied. It is demonstrated that p-MoS2/n-Si solar cell can achieve a high efficiency of 21.9%. With the appearance of MoOx, the effect of location, electron affinity and thickness of MoOx on the photovoltaic performances p-MoS2/n-Si heterojunction solar cells are studied. The efficiencies of p-MoS2/p-MoOx/n-Si solar cells are significantly reduced to be lower than 11.4%, p-MoOx/p-MoS2/n-Si solar cells maintain superior efficiencies over 20% in a large range of electron affinities lower than 3.0 eV for p-MoOx. Consequently, in modulating the Fermi level of MoS2 films through MoOx doping, p-MoOx capping layer is suggested to be located between MoS2 and front electrode rather than at p-MoS2/n-Si interface, to maintain the excellent performances of p-MoS2/n-Si solar cells.

Solution-Processed 2D Transition Metal Dichalcogenides: Materials to CMOS Electronics

ConspectusTwo-dimensional (2D) semiconducting transition metal dichalcogenides (TMDs) have demonstrated exceptional potential as materials for future complementary metal-oxide-semiconductor (CMOS) technology. This is primarily because of their atomic thickness and excellent electrical and mechanical properties. With advancements in fabrication technology, electronic devices based on 2D TMD materials have rapidly progressed from isolated units for scientific experimentation to integrated circuits with practical applications. Among the different production methods, the solution-processing of 2D TMD nanomaterial dispersions offers the distinct advantages of low-temperature processing and cost-effective manufacturing for large-scale flexible and wearable electronics. A wide range of 2D nanoflake inks with versatile electronic properties can be assembled into atomic-thick thin films with dangling-bond-free van der Waals interfaces between adjacent nanoflakes. Furthermore, direct printing techniques can easily integrate multifunctional devices, such as n-type and p-type transistors, into CMOS devices and more complex integrated circuits. Despite these benefits and previous accomplishments, the field of solution-processed CMOS electronics using 2D TMD semiconducting materials is in its early stages of development and requires further research. One of the current challenges is the production of scalable and high-purity 2D semiconductor mono- and few layers with large lateral sizes and narrow thickness distribution. The field-effect mobility of solution-processed 2D TMD transistors remains lower than that of the transistors manufactured using mechanical exfoliation and chemical vapor deposition methods. In particular, limited research has been conducted on solution-processed p-type 2D TMD transistors. As a result, solution-processed CMOS devices using n-type and p-type 2D TMD transistors are scarce. In this Account, we provide an overview of the recent progress in the field of solution-processed CMOS electronics employing 2D TMD materials. First, we introduce the basic liquid exfoliation methods, such as sonication-assisted exfoliation and molecular intercalation methods, that are commonly utilized to prepare 2D TMD dispersions. In addition, we discuss the production of monolayer 2D materials, which serve as the building blocks for fabricating atomic-thick thin films. Subsequently, we review the typical techniques for depositing 2D inks, including spin coating, drop casting, and inkjet printing. Furthermore, we outline the thin-film patterning process for each technique, which is crucial for integrating multifunctional materials in CMOS devices. Subsequently, we focus on the recent advancements in solution-processed 2D TMD transistors. Furthermore, we explore the various factors that can improve the performance of the devices with regard to charge transport and charge traps. Afterward, we highlight notable applications of solution-processed CMOS technology, such as logic circuits and ring oscillators. Finally, we provide an overview of the challenges and opportunities in the development of solution-processed 2D materials and the integration of multifunctional devices for the advancement of CMOS electronics. This Account aims to provide a comprehensive guide for readers, offering both a broad overview and an in-depth insight into solution-processed 2D material-based electronics, covering a wide range of topics from the preparation of 2D TMD ink to device fabrication and CMOS applications. Therefore, this Account is expected to drive further progress and advancements in this field and promote the realization of practical applications.

High-performance 2D WS2 photodetector enhanced by charge-transfer doping through NH3 annealing

Transition metal dichalcogenides (TMDs) are potential candidates towards the next-generation photodetector, owing to their tunable energy bandgap and strong light–matter interaction. However, the low charge-carrier mobility and insufficient quantum efficiency of TMDs-based devices restrain their optoelectronic performances. Therefore, an effective and facile doping method needs to be developed for overcoming their poor optoelectronics properties. Here, we demonstrate a controllable nondegenerate n-doping technique for 2D TMDs materials by annealing under NH3 flow. The on/off current ratio and field-effect mobility of the device after annealing treatment increases about 2 orders of magnitude and 23 times, respectively. We attribute this remarkable doping effect to the physical adsorption and chemical adsorption of NH3 as well as the associated formation of isolated sulfur vacancies, which is dynamically activated during the annealing treatment, and further verified by the atomic-scale characterization and density functional theory calculations. The annealing temperature and time present a controllable modulation on the electron doping levels of the WS2 channel. The fabricated WS2 photodetector can operate in a broad range of visible light at room temperature. At 532 nm wavelength, the responsivity of 2.97 A/W, external quantum efficiency of 699% and specific detectivity of over 1010 Jones indicate its great potential in sensitive and power-efficient photodetectors. Our results provide an effective method to realize controllable n-doping of 2D materials, aiming for fabricating high-performance 2D photodetectors.

Emerging Trends in 2D TMDs Photodetectors and Piezo-Phototronic Devices.

The piezo-phototronic effect shows promise with regards to improving the performance of 2D semiconductor-based flexible optoelectronics, which will potentially open up new opportunities in the electronics field. Mechanical exfoliation and chemical vapor deposition (CVD) influence the piezo-phototronic effect on a transparent, ultrasensitive, and flexible van der Waals (vdW) heterostructure, which allows the use of intrinsic semiconductors, such as 2D transition metal dichalcogenides (TMD). The latest and most promising 2D TMD-based photodetectors and piezo-phototronic devices are discussed in this review article. As a result, it is possible to make flexible piezo-phototronic photodetectors, self-powered sensors, and higher strain tolerance wearable and implantable electronics for health monitoring and generation of piezoelectricity using just a single semiconductor or vdW heterostructures of various nanomaterials. A comparison is also made between the functionality and distinctive properties of 2D flexible electronic devices with a range of applications made from 2D TMDs materials. The current state of the research about 2D TMDs can be applied in a variety of ways in order to aid in the development of new types of nanoscale optoelectronic devices. Last, it summarizes the problems that are currently being faced, along with potential solutions and future prospects.

Enhanced Transverse Seebeck Coefficients in 2D/2D PtSe2/MoS2 Heterostructures Using Wet-Transfer Stacking.

It is very challenging to estimate thermoelectric (TE) properties when applying millimeter-scale two-dimensional (2D) transition metal dichalcogenide (TMDC) materials to TE device applications, particularly their Seebeck coefficient due to their high intrinsic electrical resistance. This paper proposes an innovative approach to measure large transverse (i.e., in-plane) Seebeck coefficients for 2D TMDC materials by placing a low resistance (LR) semimetallic PtSe2 film on high-resistance (HR) semiconducting MoS2 (>10 MΩ), whose internal resistance is too high to measure the Seebeck coefficient, forming a heterojunction structure using wet-transfer stacking. The vertically stacked LR-PtSe2 (3 nm)/HR-MoS2 (12 nm) heterostructure film exhibits a high Seebeck coefficient > 190 μV/K up to 5 K temperature difference. This unusual behavior can be explained by an additional Seebeck effect induced at the interface between the LR-2D/HR-2D heterostructure. The proposed stacked LR-PtSe2/HR-MoS2 heterostructure film offers promising phenomena 2D/2D materials that enable innovative TE device applications.

Dopant‐Induced Giant Photoluminescence of Monolayer MoS2 by Chemical Vapor Transport

AbstractSubstitutional doping of 2D transition metal dichalcogenides (TMDCs) has been recognized as a promising strategy to tune their optoelectronic properties for a wide array of applications. However, controllable doping of TMDCs remains a challenging issue due to the natural doping of these materials. Here, the controllable growth of Ti‐doped MoS2 monolayers is demonstrated via the chemical vapor transport method, and the atomic embedded structure is confirmed by scanning transmission electron microscope with a probe corrector measurements. Furthermore, the grown Ti‐doped MoS2 monolayer exhibits giant photoluminescence (PL), 85‐fold stronger than a pristine MoS2 monolayer prepared by the same method. The giant PL enhancement is attributed to dopant‐induced O‐Ti‐S units and improved interaction between the monolayer and the mica substrate, increasing the photoluminescence quantum yield and facilitating radiation recombination. The successful growth of Ti‐doped MoS2 monolayer and the improvement of its optical and electrical properties by Ti doping may provide a promising method to engineer the optoelectronic properties of 2D TMDCs materials.

High Thermoelectric Performance of Janus Monolayer and Bilayer HfSSe

For 2D transition metal dichalcogenides (TMDs), the layer thickness has a greater impact on its thermoelectric properties. Herein, the thermoelectric properties of Janus monolayer and bilayer HfSSe are studied based on first‐principles calculations combined with Boltzmann equations, and the thermoelectric properties of bilayer HfSSe are also investigated with different stacking types. Owing to the influence of the interlayer coupling, the degradation of the phonon dispersion curve and the change of the phonon scattering intensity of the bilayer HfSSe lead to the decrease of its lattice thermal conductivity. In addition, the increase in the degeneracy of the electronic band structure of the bilayer HfSSe and the change in the density of states also change the thermoelectric transport properties of electrons. Integrating the coupling of high power factor and low thermal conductivity, the maximum ZT values at room temperature for n‐type doping are predicted as 3.24 and 5.54 for monolayer and SeHfS/SHfSe, respectively. And the ZT values increase to 3.24 and 5.54 as the temperature increases to 600 K. The result manifests that both monolayer and bilayer HfSSe are promising thermoelectric materials, and the layer thickness and stacking types also significantly affect the thermoelectric properties of the 2D TMDs materials.