Typical Transition Metal Dichalcogenide Research Articles

Chemical Vapor Deposition Growth of Atomically Thin SnSb2Te4 Single Crystals Toward Fast Photodetection

AbstractSnSb2Te4 (SST), a ternary van der Waals (vdW) material, has been widely investigated during last decades for potential applications in superconductivity, thermoelectricity, and optoelectronics. Recently, atomically thin SST has been predicted to show abnormal electronic band structure evolutions, high carrier mobility, and strong light–matter interaction. However, controllable synthesis of such SST crystals has been a huge challenge. Herein, atomically thin SST flakes are prepared via a chemical vapor deposition (CVD) method by using SbCl3, SnCl4·5H2O, and Te as the precursors. Multiple structural characterizations reveal that the SST flakes are single crystals with high crystallinity. Due to the narrow bandgap of 0.42 eV, SST‐based photodetectors have a broadband spectrum detection range from visible light through communication bands (480–1550 nm). More importantly, benefiting from a high room‐temperature carrier mobility over 300 cm2 V−1 s−1, the SST photodetectors demonstrate a response/recovery time of tens of tens of microseconds, which exceeds most typical transition metal dichalcogenide (TMDC) flakes. In addition, the photodetector maintains high performance after being exposed to the air for 2 months, suggesting good environmental stability. These excellent performances suggest that the SST flakes are promising for next‐generation optoelectronics.

Temperature dependence of hole mobility in methylated germanane field-effect transistor

Methylated germanane, a layered material in which single-layer germanium is terminated by methyl groups, was utilized as a channel material of back-gate-type FETs. Titanium (Ti) and nickel (Ni) were used as source and drain electrodes of FETs, and the FET with the Ti electrode showed ambipolar characteristics, whereas that with the Ni electrode showed p-type characteristics. The maximum hole mobility at RT is 380 cm2V−1s−1, which is higher than those of typical transition metal dichalcogenides. The mobility changes with temperature T according to the T −3/2 law at temperatures ranging from 243 to 343 K, suggesting that the major scattering factor of holes is acoustic phonons.

Synthesis and Formulation of Ternary Transition Metal Dichalcogenide Alloys for Additive Electronic Manufacturing

Compared with the most investigated graphene, layered transition metal dichalcogenides (TMDs) have received significant attention due to their various chemical compositions and great potential electronic application. In order to tailor and engineer properties of TMDs and therefore enhance their efficiency toward commercial applications, several methods have been employed including reducing dimensionality, creating inter and intra-heterostructures, introducing inter stain, and alloying. Among these, alloying via chemical vapor transport (CVT) is scalable, cost- efficient, and controllable method of tuning TMD bulk crystal properties. Alloying of TMDs can be categorized into several types including metal replacement, dichalcogenide replacement, and both metal and dichalcogenide replacement. In a typical TMD CVT reaction, high-purity precursors are mixed in a desired stochiometric ratio, vacuumed, and sealed in an ampoule to form a closed system. The resulting TMD crystal can then be used for additional processes, e.g., exfoliation to yield 2D TMD nanosheets. Additive electronics manufacturing is a promising technique for the scalable fabrication of electronic devices, including sensors and energy storage devices. For an ink to be compatible for different printing modalities the ink rheology including viscosity, surface tension, and solid requires to be tuned to obtain suitable fluid dynamic parameters for jetting the ink. This work summarizes the development, synthesis, characterization, and formulation of two-dimensional ternary TMDCs ink for aerosol jet printing (AJP) technology. Ball milling assisted liquid exfoliation is utilized for synthesizing ternary TMDs nanomaterials under controlled condition. The resulting nanomaterial is developed into nanomaterial ink compatible with AJP. Detailed analysis of the material characterization and ink properties are required to optimize the fluid dynamics and properties of the ink. After printing the formulated ink using AJP on various substrates, post-printing process techniques is required to be investigated for printed nanomaterials inks to achieve bulk-like performance for the printed structures. Our results highlight the innovations in synthesis and formulation of ternary transition metal dichalcogenide nanomaterial inks for additive manufacturing of electronic devices such as sensors, solar cells, and energy storage devices.

A universal and stable metasurface for photonic quasi bound state in continuum coupled with two dimensional semiconductors

The strong coupling of excitons to optical cavity modes is of immense importance when understanding the fundamental physics of quantum electrodynamics at the nanoscale as well as for practical applications in quantum information technologies. There have been several attempts at achieving strong coupling between excitons in two-dimensional semiconductors, such as transition metal dichalcogenides (TMDCs) and photonic quasi-bound states in the continuum (BICs). We identify two gaps in the platforms for achieving strong coupling between TMDC excitons and photonic quasi-BICs: firstly, in the studies so far, different cavity architectures have been employed for coupling to different TMDCs. This would mean that typically, the fabrication process flow for the cavities will need to be modified as one moves from one TMDC to the other, which can limit the technological progress in the field. Secondly, there has been no discussion of the impact of fabrication imperfections in the studies on the strong coupling of these subsystems so far. In this work, we address these two questions by optimizing a cavity with the same architecture, which can couple to the four typical TMDCs (MoS2, WS2, MoSe2, WSe2) and perform a detailed investigation on the fabrication tolerance of the associated photonic quasi-BICs and their impact on strong coupling.

Broadband nonlinear absorption properties of TiS2 nanosheets

Titanium disulfide (TiS2) is a typical transition-metal dichalcogenides (TMDs) with a layered structure similar to graphene, exhibiting remarkable photoelectric properties. In this study, TiS2 nanosheets were exfoliated successfully by liquid-phase exfoliation method. And the NLA properties of TiS2 nanosheets from ultraviolet to near-infrared were investigated by using an open-aperture Z-scan method. The results demonstrate that TiS2 nanosheets own excellent NLA characteristics in near infrared waveband. The excellent optical nonlinear properties of TiS2 nanosheets provide the possibility for practical applications of the TiS2 nanosheets in optical limiting fields especially in infrared waveband.

Construction of VS2 with sulfur vacancy as a superior cathode for lithium-ion batteries

As a typical transition-metal dichalcogenide (TMD), vanadium disulfide (VS2) is an excellent candidate for cathode material in lithium-ion batteries due to its metallic properties and large interlayer spacing. But they often suffer from low intercalation capacity and sluggish kinetics processes, significantly limiting their practical application. Herein, the cetyltrimethylammonium bromide (CTAB) is employed in the synthesis process to construct the sulfur (S) vacancy in VS2. The sulfur vacancy could improve its intercalation capacity and kinetics performance. In this structure, the interlayer vacancy defects could provide extra intercalation sites to improve intercalation capacity. It could induce multiple migration paths for lithium-ion (Li+) and electron (e–), enabling fast Li + migration and rapid charge transfer. It also presents favorable rate performance with a high pseudocapacitance contribution during a typical intercalation reaction. The above positive behaviors significantly promote the kinetics performance of VS2-x as a cathode material for lithium-ion batteries (smaller charge transfer resistance and high Li+ diffusion rate). Finally, this material could provide a high storage capacity of 140 mAh g−1 after 180th and favorable rate performance (55.5 mAh g−1 at 1A g−1). This work could provide a reference for improving TMD's electrochemical performance and expanding their applications.

Nano-WSe2 Is Absorbable and Transformable by Rice Plants.

As typical transition metal dichalcogenides (TMDC), tungsten selenide (WSe2) nanosheets (nano-WSe2) are widely used in various fields due to their layered structures and highly tunable electronic and magnetic properties, which results in the unwanted release of tungsten (W) and selenium (Se) into the environment. However, the environmental effects of nano-WSe2 in plants are still unclear. Herein, we evaluated the impacts and fate of nano-WSe2 and micro-WSe2 in rice plants (Oryza sativa L.). It was found that both nano-WSe2 and micro-WSe2 did not affect the germination of rice seeds up to 5000 mg/L but nano-WSe2 affected the growth of rice seedlings with shortened root lengths. The uptake and transportation of WSe2 was found to be size-dependent. Moreover, W in WSe2 was oxidized to tungstate while Se was transformed to selenocysteine, selenomethionine, SeIV and SeVI in the roots of rice when exposed to nano-WSe2, suggesting the transformation of nano-WSe2 in rice plants. The exposure to nano-WSe2 brought lipid peroxidative damage to rice seedlings. However, Se in nano-WSe2 did not contribute to the synthesis of glutathione peroxidase (GSH-Px) since the latter did not change when exposed to nano-WSe2. This is the first report on the impacts and fate of nano-WSe2 in rice plants, which has raised environmental safety concerns about the wide application of TMDCs, such as WSe2 nanosheets.

One-Step Hydrothermal Reaction Induced Nitrogen-Doped MoS2/MXene Composites with Superior Lithium-Ion Storage

MoS2, a typical transition metal dichalcogenide (TMDs), inheriting high theoretical capacity, open framework and unique electrochemical properties, is regarded as a promising electrode material. However, the low electronic conductivity and slow chemical kinetics of two-dimensional (2D) MoS2 lamellars, along with the large volume expansion during cycling hinder their application in Li-ion batteries. MXene inherits the strengths of excellent metallic conductivity, a low lithium-ion diffusion potential barrier and superior mechanical stability; however, its low reversible capacity and self-stacking problems as anode still need to be solved. Herein, the MXene Ti3C2Tx compound with MoS2 through a simple one-step hydrothermal reaction is introduced. The introduction of nitrogen-doped Ti3C2Tx can effectively restrain the volume change of MoS2 and ameliorate the electronic conductivity of the whole electrode, while MoS2 can alleviate the self-stacking of Ti3C2Tx during cycling. The as-prepared MoS2/MXene electrode delivers an initial discharge capacity of 1087 mA h g−1 with an initial Coulombic efficiency (ICE) of 81.6% at 100 mA g−1, and a specific discharge capacity of 731 mA h g−1 can be retained after 100 cycles. The excellent electrochemical performance demonstrates that nitrogen-doped MoS2/MXene can be a potential electrode material for Li-ion batteries.

Defect-Rich Monolayer MoS2 as a Universally Enhanced Substrate for Surface-Enhanced Raman Scattering.

Monolayer 2H-MoS2 has been widely noticed as a typical transition metal dichalcogenides (TMDC) for surface-enhanced Raman scattering (SERS). However, monolayer MoS2 is limited to a narrow range of applications due to poor detection sensitivity caused by the combination of a lower density of states (DOS) near the Fermi energy level as well as a rich fluorescence background. Here, surfaced S and Mo atomic defects are fabricated on a monolayer MoS2 with a perfect lattice. Defects exhibit metallic properties. The presence of defects enhances the interaction between MoS2 and the detection molecule, and it increases the probability of photoinduced charge transfer (PICT), resulting in a significant improvement of Raman enhancement. Defect-containing monolayer MoS2 enables the fluorescence signal of many dyes to be effectively burst, making the SERS spectrum clearer and making the limits of detection (LODs) below 10−8 M. In conclusion, metallic defect-containing monolayer MoS2 becomes a promising and versatile substrate capable of detecting a wide range of dye molecules due to its abundant DOS and effective PICT resonance. In addition, the synergistic effect of surface defects and of the MoS2 main body presents a new perspective for plasma-free SERS based on the chemical mechanism (CM), which provides promising theoretical support for other TMDC studies.

Intrinsic type-II van der Waals heterostructures based on graphdiyne and XSSe (X = Mo, W): a first-principles study.

Typical transition-metal dichalcogenides (TMDs) and graphdiyne (GDY) often form type-I heterojunctions, which will limit their applications in optoelectronic devices. Here, type-II heterojunctions based on GDY and TMDs are constructed by introducing Janus structures. An intrinsic type-II heterojunction is presented when the GDY is in contact with a Se-terminated layer, but a type-I heterojunction would appear when it is in contact with the S-terminated surface. Such a difference in band alignment can be attributed to the interaction between the dipole moment formed by the Janus structure and the graphdiyne layer. Furthermore, for heterojunctions in contact with the S-terminated layer, they can be converted into type-II heterojunctions by a small external electric field (for WSSe, only 0.05 V A-1 is required). This approach can suggest a convenient design strategy for the application of graphdiyne in a wider range of applications.

Toward layered MoS2 anode for harvesting superior lithium storage.

As a typical transition metal dichalcogenide (TMD), molybdenum disulphide (MoS2) has become one of the most promising anode materials for lithium-ion batteries (LIBs) due to its desirable electrochemical properties. But the development of commercial MoS2 is limited by the problem of agglomeration. Thus, the production of MoS2 nanosheets with few (<10) layers is highly desired but remains a great challenge. In this work, a facile and scalable approach is developed to prepare large-flake, few-layer (4–8) MoS2 nanosheets with the assistance of ultrasonics. Simultaneously, the as-prepared MoS2 nanosheets and commercial bulk MoS2 were analysed under multiple spectroscopic techniques and a series of electrochemical tests to understand the dependence of electrochemical performance on structural properties. When used as anode materials for LIBs, the obtained MoS2 nanosheets provide a reversible capacity of 716 mA h g−1 at 100 mA g−1 after 285 cycles, and demonstrated an excellent capacity retention rate of up to 80%. Compared with that of commercial MoS2 (14.8%), the capacity retention rate of our MoS2 nanosheets has a significant improvement. This work explored the ability of few-layered MoS2 nanosheets in the field of LIBs while suggesting the commercialization of the MoS2 by an ultrasonicated ball milling exfoliation technique.

Ultrafast and hypersensitized detection based on van der Waals connection in two-dimensional WS2/Si structure

WS2, as a typical transition-metal dichalcogenides (TMDs) with strong light–matter interaction, exhibits great potential for highly-responsive photoelectric detectors. In this work, a series of WS2 nano-films with different thicknesses are successfully prepared on Si substrate by atomic layer deposition (ALD) and present a high-performance lateral photovoltaic effect (LPE). It shows high position sensitivity (up to 232 mV mm−1) and ultrafast response speed of 4.1 μs with little signal degeneration because of the strong light absorptivity and carrier mobility in the layered structure connected by van der Waals force. In addition, we find the absorption wavelength of lateral photovoltage (LPV) has changed significantly when WS2 thickness decreases to several layers. We attribute this phenomenon to the increasing indirect band-gap of WS2. It establishes an association between materials bandgap and LPV, which may suggest a potential approach for the characterization of theof bandgap and thickness of 2D materials.

Selenium Defect Boosted Electrochemical Performance of Binder-Free VSe2 Nanosheets for Aqueous Zinc-Ion Batteries.

As a typical transition-metal dichalcogenides, vanadium diselenide (VSe2) is a promising electrode material for aqueous zinc-ion batteries due to its metallic characteristics and excellent electronic conductivity. In this work, we propose a strategy of hydrothermal reduction synthesis of stainless-steel (SS)-supported VSe2 nanosheets with defect (VSe2-x-SS), thereby further improving the conductivity and activity of VSe2-x-SS. Density functional theory calculations confirmed that Se defect can adjust the adsorption energy of Zn2+ ions. This means that the adsorption/desorption process of Zn2+ ions on VSe2-x-SS is more reversible than that on pure SS-supported VSe2 (VSe2-SS). As a result, the Zn//VSe2-x-SS battery showed more excellent electrochemical performance than Zn//VSe2-SS. The VSe2-x-SS electrode shows a good specific capacity of 265.2 mA h g-1 (0.2 A g-1 after 150 cycles), satisfactory rate performance, and impressive cyclic stability. In addition, we also have explored the energy-storage mechanism of Zn2+ ions in this VSe2-x-SS electrode material. This study provides an effective strategy for the rational design of electrode materials for electrochemical energy-storage devices.

Disorder engineering in transition metal dichalcogenides toward efficient high current density reduction electrocatalysts

In this perspective, we highlight the importance of nanoscale disorder and mesoscale morphology to enhance the activity and tune the selectivity of group VI transition metal dichalcogenide electrocatalysts toward two paramount reductions reactions as H2 evolution reaction and CO2 reduction. The strategy we propose takes advantage of the metastable nanoscale atomic arrangement of highly disordered and amorphous materials, to overcome the limits of the typical transition metal dichalcogenide crystalline catalysts. For the H2 evolution reaction, going beyond the creation of point defects in crystalline structures in favor of fully amorphous organizations not only increases the per-site activity and active surface area but also improves the conductivity and the reaction kinetics. In addition, the incorporation of nanoscale disorder promotes the formation of complex products in CO2 reduction through reaction pathways inaccessible on other sites. On the other hand, the mesoscale architecture of the catalyst controls mass transport in both the liquid and gas phase, as well as determines the real-world performance of catalysts. We suggest that by exploiting disordered nanoscale organization and controlled mesoscale features, the performances can be drastically improved to reach the state-of-art metallic electrocatalysts.

High‐Performance Broadband Tungsten Disulfide Photodetector Decorated with Indium Arsenide Nanoislands

The 2D tungsten disulfide (WS2), as a typical transition metal dichalcogenide (TMD), has aroused intense research interests in photodetection. However, the limited detection wavelength ranges and low photoresponsivity hinder its further application. To promote the application of WS2 in optoelectronics fields, indium arsenide (InAs) nanoislands decorated WS2 are utilized to fabricate photodetectors in this work. Owing to the photogating effect and localized surface plasmon resonance (LSPR), a significant enhancement of photocurrent response (≈1 mA W−1) is obtained by coupling WS2 with InAs nanoislands. Furthermore, the extended detection wavelength up to 1060 nm is realized due to the efficient light absorption in IR range of InAs nanoislands. The high performance, stability, and reliability in ambient temperature strongly indicate that the InAs nanoislands/WS2 heterostructure can be considered as a promising material for TMDs‐based broadband optoelectronic devices in the future.

Homogeneous 2D MoTe2 CMOS Inverters and p-n Junctions Formed by Laser-Irradiation-Induced p-Type Doping.

Among all typical transition-metal dichalcogenides (TMDs), the bandgap of α-MoTe2 is smallest and is close to that of conventional 3D Si. The properties of α-MoTe2 make it a favorable candidate for future electronic devices. Even though there are a few reports regarding fabrication of complementary metal-oxide-semiconductor (CMOS) inverters or p-n junction by controlling the charge-carrier polarity of TMDs, the fabrication process is complicated. Here, a straightforward selective doping technique is demonstrated to fabricate a 2D p-n junction diode and CMOS inverter on a single α-MoTe2 nanoflake. The n-doped channel of a single α-MoTe2 nanoflake is selectively converted to a p-doped region via laser-irradiation-induced MoOx doping. The homogeneous 2D MoTe2 CMOS inverter has a high DC voltage gain of 28, desirable noise margin (NMH = 0.52 VDD , NML = 0.40 VDD ), and an AC gain of 4 at 10 kHz. The results show that the doping technique by laser scan can be potentially used for future larger-scale MoTe2 CMOS circuits.

Enhanced photoluminescence of WS2/WO3 heterostructural QDs

Abstract Tungsten disulfide (WS2), as one of the typical transition-metal dichalcogenides (TMDCs), possesses attractive physical properties and widely potential applications, especially in optoelectronic devices. However, the low photoluminescence (PL) quantum yield (QY) still limits the practical applications of WS2. In this paper, WS2/WO3 heterostructural (core/shell) quantum dots (QDs) are prepared by pulsed laser deposition (PLD) and rapid thermal annealing (RTA) techniques, which exhibit PL enhancement and higher PLQY. The improvement may originate from the WO3 shells, which act as passivation layer to relieve the surface defect-states and many-body effects. Our work may provide a new pathway to utilize the heterostructural QDs to design physical properties of TMDCs, and these heterostructural QDs are promising candidates in optoelectronic applications such as photodetectors and light-emitting devices.

Ultrathin exfoliated WS2 nanosheets in low-boiling-point solvents for high-efficiency hydrogen evolution reaction

Two-dimensional mono-or few-layer WS2, as a typical transition metal dichalcogenide, usually exhibits excellent electrocatalytic hydrogen evolution reaction (HER) activity. In this work, low-boiling-point solvents are adopted for the controllable preparation of ultra-thin WS2 nanosheets by an improved liquid phase exfoliation process directly from the raw WS2 powder. The thickness of as-obtained WS2 nanosheets is about ∼1.5 nm with lateral size of ∼1.2 μm. Their HER performance was investigated by loading them onto a glass carbon electrode in 0.5M H2SO4 solution. The resulting polarization and Tafel curves indicate that the as-obtained WS2 nanosheets are effective electrocatalysts for HER with a low onset potential of 65mV and a Tafel slope of 55mV/dec. The proposed liquid phase exfoliation technique is lucrative for exfoliating transition metal disulfide materials in various applications.

Pressure induced superconductive 10-fold coordinated TaS2: a first-principles study

By crystal structure prediction and first-principles calculations, we researched the structure transformation and electronic states for a typical transition metal dichalcogenides (TMDs): 1T-TaS2 under hydrostatic pressure. The layered 1T-TaS2 will first transform to an 8-fold monoclinic C2/m phase and then to a 10-fold coordinated tetragonal I4/mmm phase which has 3D covalent bond network linked in space. Our calculations suggest that the lone pair electrons of S in 1T-TaS2, which keep the stablity of the layered structure, will be activated by pressure and participate the chemical bonding with Ta, to form the high-pressure C2/m and I4/mmm phases. Additionally, collective electronic states of superconductivity also retains in the I4/mmm phase and the critical transition temperature of superconductivity is 9 K at 100 GPa.

Dimensionally driven crossover from semimetal to direct semiconductor in layered SbAs

Two-dimensional (2D) materials have attracted a great deal of attention because they exhibit intriguing physical and chemical properties with great potential applications in electronic and optoelectronic devices, and even energy conversion. Due to the high anisotropy and unique crystal structure of layered materials, the properties can be effectively tuned by simply reducing dimensions to 2D. In this work, a unique 2D semiconductor, namely, monolayered SbAs, with high stability and indirect band gap, is predicted on the basis of first-principles calculations together with cluster expansion and Monte Carlo simulations. Interestingly, although the bulk antimony arsenide compound SbAs is known to exhibit semimetallic behavior, our calculations find that it is transformed into a direct semiconductor with a band gap of 1.28 eV when thinned down to a single atomic layer. The monolayer with antisite defects is transformed from indirect into a direct band-gap semiconductor. Such dramatic changes in the electronic structure could pave the way for SbAs to play a role in electronic device applications. Moreover, we find that the interlayer interactions in SbAs lead to a higher exfoliation energy than typical transition metal dichalcogenides such as $\mathrm{Mo}{\mathrm{S}}_{2}$, and hence we suggest that chemical deposition methods might be better than mechanical exfoliation methods for obtaining monolayer samples.