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Manipulation of the electronic properties of layered transition-metal dichalcogenides (TMDs) is of fundamental significance for a wide range of electronic and optoelectronic applications. Surface charge transfer doping is considered to be a powerful technique to regulate the carrier density of TMDs. Herein, the controllable p-type surface modification of few-layer WSe2 by FeCl3 Lewis acid with different doping concentrations have been achieved. Effective hole doping of WSe2 has been demonstrated using Raman spectra and XPS. Transport properties indicated the p-type FeCl3 surface functionalization significantly increased the hole concentration with 1.2 × 1013 cm−2, resulting in 6 orders of magnitude improvement for the conductance of FeCl3-modified WSe2 compared with pristine WSe2. This work provides a promising approach and facilitate the further advancement of TMDs in electronic and optoelectronic applications. [ABSTRACT FROM AUTHOR]

Negative differential resistance (NDR) devices show potential for advanced future computing technologies with deficient energy consumption, particularly in multivalued logic computing due to multiple threshold voltages. Here, we report an NDR phenomenon observed in a heterostructure of graphene (Gr), hexagonal boron nitride (h-BN), and tungsten diselenide (WSe2) in the negative gate voltage regime. In this structure, WSe2 is employed as a channel material aligned with a dielectric, h-BN, while Gr acts as a floating gate. The investigation of temperature-dependent electrical charge transport using the global gate allows for identifying the tunneling process within a specific range of gate voltages. In addition, the electrical charge transport measurement demonstrates significant gate-tunable NDR behavior with a maximum peak-to-valley current ratio of 7.2 at room temperature, which improved to 11.6 at a temperature of 77 K. To the best of our knowledge, this is the unique demonstration of NDR charge transport behavior in a single-channel WSe2 field-effect transistor device. This feature promises many applications, such as low-power logical circuits, memory, and high-frequency switching devices. [ABSTRACT FROM AUTHOR]

Spin and valley polarizations (Ps and PKK') and tunneling magnetoresistance (TMR) are demonstrated in the ferromagnetic/barrier/normal/barrier/ferromagnetic WSe2 junction, with the gate voltage and off-resonant circularly polarized light (CPL) applied to the two barrier regions. The minimum incident energy of non-zero spin- and valley-resolved conductance has been derived, which is consistent with numerical calculations and depends on the electric potential U, CPL intensity ΔΩ, exchange field h, and magnetization configuration: parallel (P) or antiparallel (AP). For the P (AP) configuration, the energy region with PKK' = -1 or Ps = 1 is wider (narrower) and increases with ΔΩ. As h increases, the Ps = 1 (PKK' = -1 or Ps = 1) plateau becomes wider (narrower) for the P (AP) configuration. As U increases, the energy region with PKK' = -1 increases first and then moves parallel to the EF-axis, and the energy region with Ps = 1 for the P configuration remains unchanged first and then decreases. The energy region for TMR = 1 increases rapidly with h, remains unchanged first and then decreases as U increases, and has little dependence on ΔΩ. When the helicity of the CPL reverses, the valley polarization will switch. This work sheds light on the design of spin-valley and TMR devices based on ferromagnetic WSe2 double-barrier junctions. [ABSTRACT FROM AUTHOR]

Volatile amines in breath act as biomarkers for kidney and liver diseases. Monitoring these amines, especially when present as a mixture, provides insights into the metabolic state of the body. This study focuses on differentiating volatile amines by systematically modulating the conductivity and sensitivity of WSe2/Multiwalled Carbon Nanotubes composite‐based sensors. The fabricated chemiresistive sensor array demonstrates high selectivity, sensitivity (7.67% ppm−1), fast response and recovery kinetics (32 s/137 s), and accurate discrimination among target amines, even in the presence of other VOCs (volatile organic compounds). The sensor array operates at room temperature and achieves a theoretical limit of detection (LOD) of 387 ppt, 206, 157, and 202 ppb for triethylamine (TEA), dimethylamine (DMA), methylamine (MA), and ammonia (NH3), respectively, demonstrating its suitability for breath sensing and diagnostics. Machine learning (ML) analysis is employed to differentiate between the volatile amines and mixtures with 94% accuracy. The ability to detect these amines at such low ppt and ppb levels underscores the potential of this e‐nose technology for high‐performance applications in early‐stage disease diagnostics. [ABSTRACT FROM AUTHOR]

Constructing van der Waals materials with spontaneous out-of-plane polarization through interlayer engineering expands the family of two-dimensional ferroelectrics and provides an excellent platform for enhancing the photoelectric conversion efficiency. Here, we reveal the effect of spontaneous polarization on ultrafast carrier dynamics in rhombohedral stacked bilayer WSe2. Using precise stacking techniques, a 3R WSe2-based vertical heterojunction was successfully constructed and confirmed by polarization-resolved second harmonic generation measurements. Through output characteristics and the scanning photocurrent map under zero bias, we reveal a non-zero short-circuit current in the graphene/3R WSe2/graphene heterojunction region, demonstrating the bulk photovoltaic effect. Furthermore, the out-of-plane polarization enables the 3R WSe2 heterojunction region to achieve an ultrafast intrinsic photoresponse time of approximately 3 ps. The ultrafast response time remains consistent across varying detection powers, demonstrating environmental stability and highlighting the potential in optoelectronic applications. Our study presents an effective strategy for enhancing the response time of photodetectors.

Feedback field-effect transistors (FBFETs) have been studied to obtain near-zero subthreshold swings at 300 K with a high on/off current ratio ~1010. However, their structural complexity, such as an epitaxy process after an etch process for a Si channel with a thickness of several nanometers, has limited broader research. We demonstrated a FBFET using in-plane WSe2 p−n homojunction. The WSe2 FBFET exhibited a minimum subthreshold swing of 153 mV/dec with 30 nm gate dielectric. Our modeling-based projection indicates that the swing of this device can be reduced to 14 mV/dec with 1 nm EOT. Also, the gain of the inverter using the WSe2 FBFET can be improved by up to 1.53 times compared to a silicon CMOS inverter, and power consumption can be reduced by up to 11.9%. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive simulation of a TiSe2‐based photodetector, an optoelectronic device adept at converting a spectrum of electromagnetic radiation spanning ultraviolet (UV), visible, and infrared wavelengths into electrical signals. The TiSe2 absorber material is characterized by a narrow direct bandgap of 1.2 eV, endowing the photodetector with superior optical and electronic attributes that enhance its photodetection capabilities. In‐depth analysis of the energy band diagram, the current‐voltage (J‐V) characteristics, and spectral responses is conducted. This article involves in methodical variations in the thickness, doping levels, and defect density across different layers to achieve optimal performance. The photodetector's current, JSC, and voltage, VOC are recorded at 37.30 mA cm−2 and 0.795 V, in turn. Additionally, the device achieves a peak responsivity, R of 0.67 A W−1 and a detectivity, D* of 12.9 × 1014 Jones at a wavelength of 920 nm. Notably, the spectral response is significantly enhanced between 760 and 1010 nm, indicating the photodetector's proficient detection of near‐infrared (NIR) light. The findings underscore the potential of TiSe2 as an effective material for photodetector applications, marking a significant advancement in the field and paving the way for future research endeavors in photodetector technology. [ABSTRACT FROM AUTHOR]

Here, we have grown crystalline MoSe2 and WSe2 nanostructures on thin flexible Mo and W metal foils at growth temperature of 450–550°C by using the single-zone atmospheric pressure chemical vapour deposition (CVD) method. Raman spectroscopy measurements confirm the structural formation with low line widths for MoSe2 on Mo foil at 450°C and WSe2 on W foil at 550°C corresponding to their optical vibrational Raman modes. X-ray diffraction (XRD) patterns show the hexagonal 2H phase of grown MoSe2 and WSe2 nanostructures attributed to their distinguished XRD peaks. The field emission scanning electron microscopy revealed the granular-layered MoSe2 surface, whereas the nano-woolforest type surface of WSe2 film. Elemental analysis using energy-dispersive X-ray spectroscopy technique confirms the formation of nearly stoichiometry MoSe2 and WSe2 compounds. Chemical composition and binding energy values of deposited films were studied by using X-ray photoelectron spectroscopy. Growth of polycrystalline and large-area MoSe2 and WSe2 film on flexible metal foils using scalable and low-cost CVD system paves the way for the fabrication of futuristic flexible energy devices on metal foils. [ABSTRACT FROM AUTHOR]

In recent years, there has been an increasing focus on 2D nongraphene materials that range from insulators to semiconductors to metals. As a single-elemental van der Waals semiconductor, tellurium (Te) has captivating anisotropic physical properties. Recent work demonstrated growth of ultrathin Te on WSe2 with the atomic chains of Te aligned with the armchair directions of the substrate using physical vapor deposition (PVD). In this system, a moiré superlattice is formed where micrometer-scale Te flakes sit on top of the continuous WSe2 film. Here, we determined the precise orientation of the Te flakes with respect to the substrate and detailed structure of the resulting moiré lattice by combining electron microscopy with image simulations. We directly visualized the moiré lattice using center of mass-differential phase contrast (CoM-DPC). We also investigated the local strain within the Te/WSe2 layered materials using scanning nanodiffraction techniques. There is a significant tensile strain at the edges of flakes along the direction perpendicular to the Te chain direction, which is an indication of the preferred orientation for the growth of Te on WSe2. In addition, we observed local strain relaxation regions within the Te film, specifically attributed to misfit dislocations, which we characterize as having a screw-like nature. The detailed structural analysis gives insight into the growth mechanisms and strain relaxation in this moiré heterostructure.

Quasi-bound states in the continuum (quasi-BICs) offer unique advantages in enhancing nonlinear optical processes and advancing the development of active optical devices. Here, the tunable robust quasi-BICs resonances are experimentally achieved through the engineering of multiple-hole Si-metasurface. Notably, the quasi-BICs mode exhibits flat bands with minimal dispersion at a wide range of incident angles, as demonstrated by the angle-resolved spectroscopy measurements. Furthermore, we demonstrate a giant second-harmonic generation (SHG) enhancement by coupling a WSe2 monolayer to the quasi-BICs hosted in the metasurface. Leveraging the strong local electric field and high state density of the observed quasi-BICs, the SHG from the WSe2 monolayer can be enhanced by more than two orders of magnitude. Our work paves the way for effectively enhancing nonlinear optical processes in two dimensional (2D) materials within the framework of silicon photonics and is expected to be applied in nonlinear optical devices.

This paper presents a hydrogen sensor made of WSe 2 modified monocrystalline SnSe 2 nanolayer. The hydrogen sensitive property of tungsten diselenide (WSe 2) and tin diselenide (SnSe 2) was found by hydrothermal adjustment of the molar ratio. The samples were characterized for their crystal structure, microstructure, morphology, and elemental composition, and the morphology and heterojunction formation of the nanocomposites were confirmed. When the optimal molar ratio is 1:1 and the optimal working temperature is 270 °C, the WSe 2 /SnSe 2 sensor have good sensing properties for hydrogen, and the sensitivity for 100 ppm hydrogen is about 7.27. Finally, the experiment proves that WSe 2 /SnSe 2 gas sensor has a unique selection of hydrogen and has a wide application prospect in hydrogen detection in the future. The gas sensing mechanism of the hydrogen sensor is discussed based on its material structure. • A hydrogen sensor with WSe 2 modified monocrystalline SnSe 2 was proposed. • The sensor has the best response to hydrogen at 270 °C. • The enhanced sensing mechanism with p-n heterojunction is discussed. • Hydrogen sensor has fast response and long-term stability. [ABSTRACT FROM AUTHOR]

In this paper, the first‐principles method is used to calculate the electronic structure of the intrinsic WSe2 system and the Ca adsorbed WSe2 system under shear deformation, and the diffusion barrier of Ca on WSe2 is studied in depth. The results show that shear deformation can effectively reduce the band gap of WSe2 system, and shear deformation can easily lead to the transition from semiconductor properties to metal properties. The adsorption of Ca leads to the change of the band structure of WSe2. The contribution of Ca‐d electrons leads to an increase in the peak in the range of 3–6 eV. The shear deformation reduces the diffusion barrier of Ca on the WSe2 surface. This paper provides an improvement method for the application of WSe2 in the field of battery. [ABSTRACT FROM AUTHOR]

Quasi-bound states in the continuum (quasi-BICs) offer unique advantages in enhancing nonlinear optical processes and advancing the development of active optical devices. Here, the tunable robust quasi-BICs resonances are experimentally achieved through the engineering of multiple-hole Si-metasurface. Notably, the quasi-BICs mode exhibits flat bands with minimal dispersion at a wide range of incident angles, as demonstrated by the angle-resolved spectroscopy measurements. Furthermore, we demonstrate a giant second-harmonic generation (SHG) enhancement by coupling a WSe2 monolayer to the quasi-BICs hosted in the metasurface. Leveraging the strong local electric field and high state density of the observed quasi-BICs, the SHG from the WSe2 monolayer can be enhanced by more than two orders of magnitude. Our work paves the way for effectively enhancing nonlinear optical processes in two dimensional (2D) materials within the framework of silicon photonics and is expected to be applied in nonlinear optical devices. [ABSTRACT FROM AUTHOR]

Semi‐floating gate field‐effect transistors (SFG‐FETs) based on 2D materials have received much attention due to their unique optoelectronic characteristics, potential applications in near‐memory computing and constructing sensing‐memory‐processing units. Here, the non‐volatile and gate‐controlled multistate photovoltaic response of a WSe2/h‐BN/graphene SFG‐FET is investigated both in experimental and theoretical aspects. Due to the ambipolar carrier transport of WSe2 channel, both electrons and holes can be stored in the graphene floating gate layer, which results in two evident memory windows on the round sweep transfer characteristic curve. Different charge‐stored states of the SFG layer enable the channel to form a lateral junction that can be adjusted by the gate voltage, which leads to the gate‐controlled multistate photovoltaic response. A theoretical model is implemented to explain the memory and the multistate photovoltaic response behaviors in a quasi‐quantitative level. The relationship between the charge‐stored states in the SFG and the photo‐response, as well as its dependence on the gate voltage are systematically analyzed. These research results provide a reliable way for realizing high‐performance multi‐functional photodetectors based on SFG‐FETs and for thorough understanding the complicated optoelectronic behaviors of SFG‐FETs. [ABSTRACT FROM AUTHOR]

Two-dimensional transition metal dichalcogenide (TMDC) semiconductors are emerging as strong contenders for electronic devices that can be used in highly radioactive environments such as outer space where conventional silicon-based devices exhibit nonideal characteristics for such applications. To address the radiation-induced interface effects of TMDC-based electronic devices, we studied high-energy proton beam irradiation effects on the electrical properties of field-effect transistors (FETs) made with tungsten diselenide (WSe2) channels and hexagonal boron-nitride (hBN)/SiO2 gate dielectrics. The electrical characteristics of WSe2 FETs were measured before and after the irradiation at various proton beam doses of 1013, 1014, and 1015 cm−2. In particular, we demonstrated the dependence of proton irradiation-induced effects on hBN layer thickness in WSe2 FETs. We observed that the hBN layer reduces the WSe2/dielectric interface effect which would shift the transfer curve of the FET toward the positive direction of the gate voltage. Also, this interface effect was significantly suppressed when a thicker hBN layer was used. This phenomenon can be explained by the fact that the physical separation of the WSe2 channel and SiO2 dielectric by the hBN interlayer prevents the interface effects originating from the irradiation-induced positive trapped charges in SiO2 reaching the interface. This work will help improve our understanding of the interface effect of high-energy irradiation on TMDC-based nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Context: In this paper, the effects of torsional deformation on the electronic properties of intrinsic WSe2 system and Ca-adsorbed WSe2 system were systematically studied by first-principles method. The results show that Ca can be stably adsorbed on the vacancy (H site) of WSe2 surface in all deformation systems, and the adsorption energy of the system without deformation is the highest. Intrinsic WSe2 is a semiconductor with a direct band gap of 1.53 eV. The torsional deformation makes WSe2 change from a direct band gap semiconductor to an indirect band gap semiconductor and finally to a metal property. The adsorption of Ca makes the conduction band of WSe2 move down and increases the number of peaks in the conduction band region. The new density of state peaks are mainly derived from the contribution of W-d, Se-p, and d orbitals of adsorbed atoms in each adsorption system. Mulliken charge analysis shows that Ca transfers most of the valence electrons to the substrate, and the torsional deformation changes the amount of transferred charge. The twist deformation reduces the diffusion barrier of Ca on WSe2 surface from 0.20 to 0.14 eV. The above results provide a basis for the improved application of WSe2 in ion batteries. Methods: In this study, all the first-principles calculations are based on Materials Studio 8.0 software package. The generalized gradient approximation (GGA) functional Perdew-Burke-Ernzerhof (PBE) is used for the electron exchange correlation interactions in all systems. The optimization algorithm uses Broyden-Fletcher-Goldfarb-Shanno (BFGS) to optimize the model structure and calculate the energy. The measured cutoff energy is optimized to 450 eV, and the radius of the vacuum layer in the Z-axis direction is 20 Å. The K-point of 7 × 7 × 1 is selected by Monkhorst–Pack method. The structural optimization criterion is selected, the convergence radius of the force is 0.01 eV/Å, and the displacement radius between atoms is within 0.001 Å distance. The energy convergence radius of each atom is less than 1.0 × 10−6 eV/atom. [ABSTRACT FROM AUTHOR]

Narrow bandgap 2D layered material platinum selenide (PtSe2) with good environmental stability, high carrier mobility, and high light absorption, has been widely investigated for uncooled midwave‐infrared (MWIR) photodetection. However, the phototransistor based on the PtSe2 operation at room temperature suffered from the high dark current and background noise. Here, a graphene (G)‐enhanced G‐WSe2/PtSe2 hetero‐diode placed on a metal electrode is reported. To enhance the photogain, a graphene layer placed on the WSe2/PtSe2 heterodiode as a local gating layer is designed. The device exhibits an ultra‐high light on/off ratio of up to 108 and ultra‐fast photoresponse speed with raising time τr = 0.9 µs and decay time of τd = 1.5 µs in the visible spectra range. Notably, ultrabroad band photoresponse from 405 to 3366 nm is demonstrated under the self‐power model. Notably, the device presented a competitive photovoltaic effect with a high energy conversion efficiency (PCE) of 3.45%. The results pave the way toward a new approach to tuning the performance of the atomic thin layered materials photodetector. [ABSTRACT FROM AUTHOR]

Low-dimension materials such as transition metal dichalcogenides (TMDCs) have received extensive research interest and investigation for electronic and optoelectronic applications. Due to their unique widely tunable band structures, they are good candidates for next-generation optoelectronic devices. Particularly, their photoluminescence properties, which are fundamental for optoelectronic applications, are highly sensitive to the nature of the band gap. Monolayer TMDCs in the room temperature range have presented a direct band gap behavior and bright photoluminescence. In this work, we investigate a popular TMDC material WSe2's photoluminescence performance using a Raman spectroscopy laser with temperature dependence. With temperature variation, the lattice constant and the band gap change dramatically, and thus the photoluminescence spectra are changed. By checking the photoluminescence spectra at different temperatures, we are able to reveal the nature of direct-to-indirect band gap in monolayer WSe2. We also implemented density function theory (DFT) simulations to computationally investigate the band gap of WSe2 to provide comprehensive evidence and confirm the experimental results. Our study suggests that monolayer WSe2 is at the transition boundary between the indirect and direct band gap at room temperature. This result provides insights into temperature-dependent optical transition in monolayer WSe2 for quantum control, and is important for cultivating the potential of monolayer WSe2 in thermally tunable optoelectronic devices operating at room temperature. [ABSTRACT FROM AUTHOR]

Chemical modification is a powerful strategy for tuning the electronic properties of 2D semiconductors. Here we report the electrophilic trifluoromethylation of 2D WSe2 and MoS2 under mild conditions using the reagent trifluoromethyl thianthrenium triflate (TTT). Chemical characterization and density functional theory calculations reveal that the trifluoromethyl groups bind covalently to surface chalcogen atoms as well as oxygen substitution sites. Trifluoromethylation induces p‐type doping in the underlying 2D material, enabling the modulation of charge transport and optical emission properties in WSe2. This work introduces a versatile and efficient method for tailoring the optical and electronic properties of 2D transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals layered materials have been explored in depth. They can be vertically stacked into a 2D heterostructure and represent a fundamental way to explore new physical properties and fabricate high-performance nanodevices. However, the controllable and scaled growth of non-layered quasi-2D materials and their heterostructures is still a great challenge. Here, we report a selective two-step growth method for high-quality single crystalline CrTe/WSe2 and CrTe/MoS2 heterostructures by adopting a universal CVD strategy with the assistance of molten salt and mass control. Quasi-2D metallic CrTe was grown on pre-deposited 2D transition metal dichalcogenides (TMDC) under relatively low temperatures. A 2D CrTe/TMDC heterostructure was established to explore the interface's structure using scanning transmission electron microscopy (STEM), and also demonstrate ferromagnetism in a metal–semiconductor CrTe/TMDC heterostructure. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDCs) are a promising class of two‐dimensional (2D) materials for flexible electronic applications due to their low integration temperature, good electronic properties, and excellent mechanical flexibility. Moreover, TMDCs offer the possibility of co‐integrating both n‐ and p‐type transistors on the same substrate, enabling the realization of complementary metal‐oxide‐semiconductor (CMOS) circuits. In this study, n‐type MoS2 field‐effect transistors (FETs), and p‐type WSe2‐FETs integrated on a flexible foil substrate fabricated by standard thin‐film technology are presented. These devices exhibit high stability in their electronic operation under strain and repeated bending cycles. A CMOS inverter based on these transistors is also successfully demonstrated, which shows excellent switching behaviour with high gain (up to 100), high noise margin (0.87 · VDD), and low average static power consumption (40 pW). [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenides (TMDCs) are a promising class of two‐dimensional (2D) materials for flexible electronic applications due to their low integration temperature, good electronic properties, and excellent mechanical flexibility. Moreover, TMDCs offer the possibility of co‐integrating both n‐ and p‐type transistors on the same substrate, enabling the realization of complementary metal‐oxide‐semiconductor (CMOS) circuits. In this study, n‐type MoS2 field‐effect transistors (FETs), and p‐type WSe2‐FETs integrated on a flexible foil substrate fabricated by standard thin‐film technology are presented. These devices exhibit high stability in their electronic operation under strain and repeated bending cycles. A CMOS inverter based on these transistors is also successfully demonstrated, which shows excellent switching behaviour with high gain (up to 100), high noise margin (0.87 · VDD), and low average static power consumption (40 pW). [ABSTRACT FROM AUTHOR]

In this study, we simulated the performance of solar cells using appropriate optical and electrical parameters for MoX2 compounds. We used the solar cell capacitance simulator software to simulate MoS2-based solar cells with two structures (ZnO/WS2/MoS2 or ZnO/WSe2/MoS2). We investigated the impact of varying the thickness of the MoS2 absorbing layer, doping, temperature elevation, and exploring the effect of the buffer layer on the electrical characteristics of the solar cell, including parameters like open-circuit voltage (Voc), short-circuit current (Jsc), and solar cell efficiency (η). This analysis aimed to provide valuable insights into optimizing the design and performance of MoS2-based solar cells, contributing to advancements in thin-film solar cell technology. [ABSTRACT FROM AUTHOR]

Tungsten tungsten WSe2 has many excellent performance, and has excellent potential in the application of spin electronics and optoelectronics. Studying the electronic structure of defect WSe, helps to understand the effects of loading and scattering. Tt is of great significance in the application of electron and optoelectric computers. Based on the theory of density general letters, this article has studied the effects of five points of defects on the electronic structure and optical nature of WSe2 Studies have found that after analysis defects with differences, the control capabilities of the single-layer WSe2, are strong, and some defect models enhance the conductivity of the materiaL The optical properties of the material after the introduction of defects have changed significantly. Compared with the structure of this sign, the absorption edges have red shifts, which has a stronger long wave absorption ability. These theoretical results show that the introduction of defects can indeed regulate the electronic structure and optical properties of WSe2, which provides theoretical support in the transport electronics and photonology of two-dimensional carrier. [ABSTRACT FROM AUTHOR]

The experimentally newly synthesized MoSi2N4 (MSN) has attracted much attention due to its unique septuple - atomic layers structure and electronic properties. In this work, a two-dimensional MSN/WS hetero- structure stacked by a two-dimensional MSN vertically with a two-dimensional WSe2 (WS) is constructed and its electronic properties is calculated based on the first - principles calculations, which exhibits direct gap semiconductor properties with a band gap of 1. 46 eV and type - I band alignment. A weak built-in electric field from the charge depletion layer MSN to the charge accumulation layer WS exists at the interface of the hetero- structure. Finally, the two-dimensional MSN/WS heterostructure is modulated by applying the biaxial strain. It is found that under the positive biaxial strain, the MSN/WS heterostructure maintains the original direct band gap semiconductor and type-1 band alignment properties. Under the negative biaxial strain, the MSN/WS heterostructure changes from the original direct bandgap semiconductor to the indirect band gap semiconductor, and when the applied negative biaxial strain reaches -6% and -8%, the type I band alignment changes to the type II band alignment. [ABSTRACT FROM AUTHOR]

This letter reports Al/Red Phosphorus (RP)/WSe2/ITO heterostructure based self-powered UV photodetector designed by low-cost solution technique. The p–n junction is formed between p-type WSe2 and n-type red phosphorus (RP) material deposited over ITO coated PET substrate. The designed photodetector device shows Responsivity R s (A/W) of 0.23 and 0.12 (voltage bias ~ 2 V) at 300 nm and 350 nm wavelength, respectively. The rise and fall time of the device are obtained as ~ 0.19 µs and ~ 0.12 µs in UV region. [ABSTRACT FROM AUTHOR]

Currently, as the electromagnetic (EM) environment becomes increasingly complex, single-function EM materials can hardly resist the increasing electromagnetic interference (EMI), and there is an urgent need to develop multifunctional EM materials. In this work, multifunctional WSe2/Co3C was prepared by simple hydrothermal methods. Its dielectric performance and EM response were investigated. Efficient absorption, shielding performance, and energy conversion devices were customized. By tailoring the loading content, WSe2/Co3C can switch between EM absorption and EMI shielding. The maximum shielding effectiveness (SE) of WSe2/Co3C reached 36 dB, and high reflection loss (RL) of −60.28 dB and wide effective absorption bandwidth (EAB) of 6.16 GHz can be obtained at low thickness. The multiple EM attenuation mechanisms brought by the combination of two-dimensional (2D) WSe2 and magnetic Co3C are considered to be the main reason for the enhanced EM attenuation ability. The WSe2/Co3C composite provides a viable candidate for developing multifunctional EM materials in 2–18 GHz. [ABSTRACT FROM AUTHOR]

Lack of transparent contacts has been a critical bottleneck for the two-dimensional Transition Metal Dichalcogenides (TMDs) Field Effect Transistors (FETs). In the absence of approaches to introduce physical doping without inducing crystal damage, charge transfer-based doping has been widely adopted. This manuscript presents a unique charge transfer doping technique using potassium iodide (KI) solution for Selenium-based TMDs, which resulted in charge transfer/doping near the contact edges; however, unlike earlier reports, it doesn’t affect the channel region in the presence of the dopant (i.e., KI). Density functional theory (DFT) based computations are used to investigate these unique experimental observations. DFT calculations show the formation of unique mid-gap states and doping of the TMD region near the contact edge where both KI and Ni were present, which otherwise was missing in the channel region where only KI was present.

Here, we report the fabrication of high-performance printable WSe2 transistors via the doping of p-type FeCl3 molecules (hole mobility: ∼1.5 cm2 V−1 s−1; on/off ratio: ∼106). A complementary inverter is demonstrated with p-WSe2 and n-MoS2 transistors, which highlights its potential for application in future two-dimensional material-based printable electronics.

It is impossible to imagine modern electronic circuitry without a p–n junction—an essential building block for transistors, rectifiers, amplifiers, photovoltaics, etc. Conventional fabrication processes (ion implantation or chemical diffusion) result in an immutable potential configuration depriving reconfigurability. In contrast, the superior electrostatic tunability, dangling bonds‐ and reconstruction‐free interfaces are some of the key features of 2D based heterostructures, making them promising candidates for cutting‐edge optoelectronic and memory applications. Herein, the intercoupled 2D ferroelectricity of 훼‐In2Se3 is utilized to introduce micron‐scale, non‐volatile electrostatic doping in ambipolar WSe2, enabling reconfigurable p–n junction. The actuation mechanism is based on the strong polarization field along the edge topology of In2Se3. The fabricated device presents stable p–n to n–p switching, a superior rectification ratio of ≈106, and a low leakage current of ≈10−12 A. Furthermore, the switchable short‐circuit current response is utilized to demonstrate a novel self‐powered, non‐volatile memory based on photovoltaic reading. The ferroelectric non‐volatility coupled with the ability to control the device operation using optical and electrical signals paves the way for ultrathin energy‐efficient, multi‐level optoelectronic and in‐memory logic devices. [ABSTRACT FROM AUTHOR]

The excellent physicochemical properties of two-dimensional transition-metal dichalcogenides (2D TMDCs) such as WS2 and WSe2 provide potential benefits for biomedical applications, such as drug delivery, photothermal therapy, and bioimaging. WS2 and WSe2 have recently been used as chemosensitizers; however, the detailed molecular basis underlying WS2- and WSe2-induced sensitization remains elusive. Our recent findings showed that 2D TMDCs with different thicknesses and different element compositions induced autophagy in normal human bronchial epithelial cells and mouse alveolar macrophages at sublethal concentrations. Here, we explored the mechanism by which WS2 and WSe2 act as sensitizers to increase lung cancer cell susceptibility to chemotherapeutic agents. The results showed that WS2 and WSe2 enhanced autophagy flux in A549 lung cancer cells at sublethal concentrations without causing significant cell death. Through the autophagy-specific RT2 Profiler PCR Array, we identified the genes significantly affected by WS2 and WSe2 treatment. Furthermore, the key genes that play central roles in regulating autophagy were identified by constructing a molecular interaction network. A mechanism investigation uncovered that WS2 and WSe2 activated autophagy-related signaling pathways by interacting with different cell surface proteins or cytoplasmic proteins. By utilizing this mechanism, the efficacy of the chemotherapeutic agent doxorubicin was enhanced by WS2 and WSe2 pre-treatment in A549 lung cancer cells. This study revealed a feature of WS2 and WSe2 in cancer therapy, in which they eliminate the resistance of A549 lung cancer cells against doxorubicin, at least partially, by inducing autophagy. [ABSTRACT FROM AUTHOR]

Designing of high-performance, low-cost, and nonprecious metal-based bifunctional electrocatalysts is highly significant for the development of water splitting process and expanding the practical application of green hydrogen production. Transition metal dichalcogenides (TMDs) with intrinsic physical and chemical properties have been considered potential catalytic materials for electrode fabrication. However, it has remained challenging to develop TMD catalysts that have bifunctional properties for overall water splitting. Herein, WSe 2 , as a typical representative of TMDs, was utilized to design electrocatalysts using polypyrrole (PPy) or polyaniline (PANI) as a conducting polymer (CP) and cobalt doping. A facile hydrothermal preparation of WSe 2 in the presence of CP enabled the construction of cobalt-doped WSe 2 @CP electrocatalysts. Morphological analysis indicated that the CP played an important role as a conductive template to enhance the distribution of WSe 2 nanosheets, leading to higher surface area. In addition, cobalt doping led to the formation of defect structures and boosted the electrocatalytic activities of the catalysts for oxygen evolution reaction (OER). Owing to the increased electrochemical surface area and defect structures, the cobalt-doped WSe 2 @CP nanostructures exhibited enhanced electrochemical properties for hydrogen evolution reaction (HER) and OER in an alkaline medium. The cobalt-doped WSe 2 @PANI modified glassy carbon electrode (GCE) exhibited overpotentials down to 308 and 360 mV at a current density of 10 mA cm−2 for the HER and OER, respectively. Furthermore, the cobalt-doped WSe 2 @CP electrocatalysts demonstrated long-term stability and continuous cycling. More importantly, the Co–WSe 2 @PANI electrolyzer required cell voltage of 1.87 V at a current density of 10 mA cm−2 for overall water splitting process. This work provides new findings for designing efficient bifunctional electrocatalysts utilizing TMD materials and conducting polymers. [Display omitted] • Conducting polymer templated and cobalt-doped WSe 2 electrocatalysts were prepared. • Conducting polymers enhanced the catalytic performance of WSe 2 in water splitting. • Incorporation of cobalt enhanced the activity of WSe 2 for both HER and OER. • New WSe 2 -based catalysts have bifunctional activities for overal water splitting. [ABSTRACT FROM AUTHOR]

The engineering of stacking order plays an important role in regulations of electronic and optical properties of layered van der Waals materials. Here, we demonstrate a developed physical vapour deposition approach to grow WSe 2 atomic layers with controllable 3R and 2H phases. The 3R WSe 2 bilayer tends to form at a lower deposition temperature (830 ​°C), and the 2H WSe 2 bilayer prefers to grow at a higher deposition temperature (930 ​°C). Efficient phase engineering was demonstrated by simply controlling the deposition temperature. Moreover, by photoluminescence, Raman, selected area electron diffraction and so on, it was determined that the AA'-stacking corresponds to the 2H phase, and the AB-stacking corresponds to the 3R phase. So, different layer stacking and interlayer coupling result in differences in the optical and optoelectronic properties of the two phases. The responsivity of 3R bilayer WSe 2 is ∼195 times higher than 2H phase exhibiting dramatically improved photoelectric detection performance by phase engineering (R 3R ​= ​2.54 A/W vs R 2H ​= ​0.013 A/W at 780 ​nm, 82.7 ​mW ​cm−2). Hence, the findings of this study not only contribute to the controllable synthesis of two-dimensional materials with diverse stacking phases but also hold promise for advancing the design and fabrication of future optoelectronic devices. [ABSTRACT FROM AUTHOR]

Photodetectors that can achieve high‐speed photoresponse and high responsivity with broadband detection are essential for bio‐health monitoring, imaging, chemical sensing, and many other applications. Herein a high‐performance inorganic–organic hybrid photodetector based on a heterojunction of exfoliated 2D tungsten diselenide (WSe2) layers and solution‐processable poly(3‐hexylthiophene‐2,5‐diyl), P3HT is reported. The heterojunction shows enhanced exciton harvesting through long‐range energy transfer from P3HT to WSe2, which is confirmed using photoluminescence quenching and fluorescence decay measurements. The detector shows broadband light detection from visible to near‐infrared (NIR) (400−1100 nm), and air‐stable device performance. The device exhibits the highest responsivity of 17.6 AW−1 for low incident light intensity (<10−5 W cm−2) at 640 nm wavelength of light. Furthermore, a fast photoresponse speed with a rise/fall time of 9.5/5.1 µs, which retained its performance for more than four months under ambient conditions is demonstrated. The superior device performance presented here using an inorganic–organic hybrid heterojunction is the key to producing novel high‐performance and air‐stable photodetectors with broad spectral bandwidth. [ABSTRACT FROM AUTHOR]

Monochromatic Cr Kα radiation (5414.8 eV) was used to acquire high-energy photoelectron spectroscopy data on pure W and bulk WSe2 compound. The reported spectra include a survey scan and high-resolution W 3p1/2, W 3p3/2, W 3d3/2, W 3d5/2, W 4s, W 4p1/2, W 4p3/2, W 4d, W 4f, Se 2s, Se 2p1/2, Se 2p3/2, Se 3s, and Se 3p core-levels. The data will be useful as reference core-level spectra for HAXPES studies on tungsten and its compounds. [ABSTRACT FROM AUTHOR]

Here, we report the fabrication of high-performance printable WSe2 transistors via the doping of p-type FeCl3 molecules (hole mobility: ∼1.5 cm2 V−1 s−1; on/off ratio: ∼106). A complementary inverter is demonstrated with p-WSe2 and n-MoS2 transistors, which highlights its potential for application in future two-dimensional material-based printable electronics. [ABSTRACT FROM AUTHOR]

The vertical electronic and optoelectronic devices based on 2D materials have shown great advantages over lateral devices, such as higher current density, faster switch speed, and superior short-channel control. However, it is difficult to fabricate vertical device with conventional metal deposition methods due to the aggressive process usually results in damage to the contact region. Here, we develop a simple and effective metal transfer technique and fabricate p-type and n-type WSe2 transistors by using metals with different work functions and subsequently create a vertical WSe2 transistors with a 18-nm-thick channel, which retain good gate coupling effect. Furthermore, a vertical WSe2 photodiode is constructed with graphene and Pt as asymmetric van der Waals (vdW) contacts. The work-function difference between graphene and Pt generates a built-in electric filed, leading to a high current rectification over 105. Under 405 nm laser illumination, the device exhibits excellent self-powered photodetection properties, including a high responsivity of 0.28 A W−1, fast response speed of 24 μs, and large light on/off ratio exceeding 105 at zero bias, which surpass most of the vdW photodiodes. This work demonstrates that the metal transfer technique is a promising strategy for the construction of high-performance vertical optoelectronic devices.

Low-dimension materials such as transition metal dichalcogenides (TMDCs) have received extensive research interest and investigation for electronic and optoelectronic applications. Due to their unique widely tunable band structures, they are good candidates for next-generation optoelectronic devices. Particularly, their photoluminescence properties, which are fundamental for optoelectronic applications, are highly sensitive to the nature of the band gap. Monolayer TMDCs in the room temperature range have presented a direct band gap behavior and bright photoluminescence. In this work, we investigate a popular TMDC material WSe2’s photoluminescence performance using a Raman spectroscopy laser with temperature dependence. With temperature variation, the lattice constant and the band gap change dramatically, and thus the photoluminescence spectra are changed. By checking the photoluminescence spectra at different temperatures, we are able to reveal the nature of direct-to-indirect band gap in monolayer WSe2. We also implemented density function theory (DFT) simulations to computationally investigate the band gap of WSe2 to provide comprehensive evidence and confirm the experimental results. Our study suggests that monolayer WSe2 is at the transition boundary between the indirect and direct band gap at room temperature. This result provides insights into temperature-dependent optical transition in monolayer WSe2 for quantum control, and is important for cultivating the potential of monolayer WSe2 in thermally tunable optoelectronic devices operating at room temperature.

Non-destructive and reversible modulations of polarity and carrier concentration in transistors are essential for complementary devices. The fabricated multi-gated WSe2 devices obtain dynamic electrostatic field induced electrically configurable functions and demonstrate as diode with high rectification ratio of 4.1 × 105, as well as n- and p-type inverter with voltage gain of 19.9 and 12.1, respectively. Benefiting from the continuous band alignment induced modulation of channel underneath the dual gates, the devices exhibit high-performance photodetection in wide spectral range. The devices yield high photo-responsivity (5.16 A W-1) and large 'light/'dark ratio (1 × 105). Besides, the local gate fields accelerate the separation of photo-induced carriers, leading to fast response without persistent current. This strategy takes the advantage of the simplified design and continues to deliver integrated circuits with high density. The superior electrical and photodetection characteristics exhibit great potency in the domain of future optoelectronics. [ABSTRACT FROM AUTHOR]